Showing papers on "Excimer published in 2022"

Host‐guest Complexation‐induced Aggregation based on Pyrene‐modified Cyclodextrins for Improved Electronic Circular Dichroism and Circularly Polarized Luminescence

Abstract: Abstract: Several γ-cyclodextrin (CD) derivatives mono- or di-substituted by pyrenes at the primary rim of CD were demonstrated to aggregate into nano-strips in aqueous solutions, with the pyrene moieties interpenetrating into g-CD cavities. The hydrophobic complexation-induced aggregation provides a rigid chiral environment for the pyrenes and leads to significant ECD and CPL activities, giving unprecedently high g abs and g lum values up to 4.3 × 10 -2 and 5.3 × 10 - 2 , respectively. The aggregates lead to excimer emission with high quantum yields and show B CPL and B i CPL up to 338. 6 M -1 cm - 1 and 169.3 M -1 cm - 1 , respectively.

High‐Performance Circularly Polarized Electroluminescence with Simultaneous Narrowband Emission, High Efficiency, and Large Dissymmetry Factor

Abstract: Organic light‐emitting diodes (OLEDs) that can simultaneously achieve narrowband emission, high efficiency, and circularly polarized luminescence remain a formidable challenge. In this study, a simple strategy is developed to address this challenge. A chiral exciplex‐forming co‐host is first designed by employing a chiral donor and an achiral acceptor molecule. The chiral exciplex host enables an achiral green multiple‐resonance thermally activated delayed fluorescence emitter to achieve high‐performance circularly polarized electroluminescence (CP‐EL) with a high external quantum efficiency of 33.2%, large electroluminescence dissymmetry factor of 2.8 × 10−3, and a small full‐width at half‐maximum of 42 nm. This work provides a general approach for realizing CP‐EL using easily available achiral emitters and can significantly extend the scope of circularly polarized OLEDs.

Binaphthyl-Bridged Pyrenophanes: Intense Circularly Polarized Luminescence Based on a D2 Symmetry Strategy.

Abstract: A series of D 2 -symmetric macrocycles composed of alternately linked pyrene and binaphthyl moieties (binaphthyl-bridged pyrenophanes) have been synthesized. Among them, a pyrenophane possessing ether linkers at the 2,7-positions of the pyrenes exhibited intense circularly polarized luminescence (CPL) with a | g lum | value of 0.053. This value is by far the highest for excimers and was not sensitive to temperature, solvent, or concentration. The CPL originated from a twisting pyrene excimer, with the ( R )-binaphthyl moieties producing a left-handed twist excimer, which exhibited (-)-CPL. The electric and magnetic transition dipole moments are perfectly parallel, which is the best relationship for strong CPL.

Solution-processed white OLEDs with power efficiency over 90 lm W-1 by triplet exciton management with a high triplet energy level interfacial exciplex host and a high reverse intersystem crossing rate blue TADF emitter.

Abstract: Solution-processed white organic light-emitting diodes (WOLEDs) have shown much lower device efficiency than their vacuum-deposited counterparts, due to the lack of triplet exciton management in a single-emissive-layer device structure, which will induce triplet-triplet annihilation (TTA) and triplet-polaron annihilation (TPA). Here, two kinds of solution-processed WOLEDs, including thermally activated delayed fluorescence (TADF)/phosphorescence hybrid WOLEDs and all-TADF WOLEDs, with high power efficiency are developed by using a high triplet energy level (T1) interfacial exciplex as a host and a high reverse intersystem crossing (RISC) rate TADF emitter as a blue dopant for triplet exciton management. The interfacial exciplex host with high T1 can ensure that triplet excitons transfer from the host to the blue emitter, and the blue TADF emitter with high RISC rate (1.15 × 107 s-1) can rapidly upconvert triplet excitons to singlet ones to avoid TTA and TPA. The solution-processed TADF/phosphorescence hybrid and all-TADF WOLEDs exhibit maximum external quantum efficiencies of 31.1% and 27.3%, together with maximum power efficiencies of 93.5 and 70.4 lm W-1, respectively, which are the record efficiencies for solution-processed WOLEDs, and quite comparable to those of most vacuum-deposited counterparts.

Tunable Fluorescence and Afterglow in Organic Crystals for Temperature Sensing

Abstract: The modulation of the properties of emission from multiple emission states in a single-component organic luminescent material is highly desirable in data anticounterfeiting, information storage, and bioapplications. Here, a single-component luminescent organic crystal of difluoroboron diphenyl β-diketonate with controllable multiple emission colors is successfully reported. The temperature-dependent luminescence experiments supported by high-level theoretical calculations demonstrate that the ratio of the fluorescence between the monomer and excimer and the phosphorescence maxima of the excimer can be effectively regulated. In addition, the temperature-dependent fluorescence and afterglow dual-emission color changes provide a new strategy for the design of highly accurate double-checked temperature sensors.

Pyrene-based monomer-excimer dual response organosilicon polymer for selective detection of 2,4,6-trinitrotoluene (TNT) and 2,4,6-trinitrophenol (TNP)

Abstract: The formation or destruction of pyrene excimer with strong emission change make it a versatile fluorophore to construct excimer emission-based fluorescence probes for various analytes detection. The distinct difference between...

Switching between intramolecular charge transfer and excimer emissions in solids based on aryl-modified ethynyl‒o-carboranes

Abstract: Because of its unique electronic properties, o-carborane has attracted attention as a scaffold for constructing solid-state luminescent materials. Here, we report stimulus-responsive luminochromic materials based on polycyclic aromatic hydrocarbon (PAH), such as anthracene and pyrene, modified with the ethynyl-o-carborane unit. Initially, luminochromism originating from switching of different emission mechanisms is described between intramolecular charge transfer (ICT) emission and excimer emission triggered by mechanical stimuli, heat, and vapor annealing regarding the single o-carborane-substituted anthracene. Next, the luminescence properties of two ethynyl-o-carboranes at both ends of PAHs are presented. In particular, multi-step mechanochromic luminescence of the pyrene derivative is explained. Stepwisely changes triggered by weak stimuli that can induce cracking sites, followed by luminochromic behavior and by grinding treatment, which causes phase transition from crystal to amorphous, leading to luminescent mechanism changes from ICT emission to excimer emission.

Direct demonstration of triplet excimer in purely organic room temperature phosphorescence through rational molecular design

Abstract: Organic luminogens with room temperature phosphorescence (RTP) have been paid great attention and developed rapidly for their wide application values. Until now, the internal mechanism and source of phosphorescence are still obscure, especially for the relationship between molecular dimer and RTP emission. Hence, we designed and synthesized eight phenothiazine 5,5-dioxide derivatives to directly reveal how the monomer and dimer in packing affect the RTP behavior. Dimers with strong π-π stacking (θ < 20.66°; d < 3.86 Å) lead to pure triplet excimer emission, while those with weak π-π stacking (27.02°< θ < 40.64°; 3.84 Å < d < 4.41 Å) contribute to dual RTP emissions of both monomer and triplet excimer. The valuable information of this work would promote the further development of this research field, as well as others in aggregate.

Direct demonstration of triplet excimer in purely organic room temperature phosphorescence through rational molecular design

Abstract: Organic luminogens with room temperature phosphorescence (RTP) have been paid great attention and developed rapidly for their wide application values. Until now, the internal mechanism and source of phosphorescence are still obscure, especially for the relationship between molecular dimer and RTP emission. Hence, we designed and synthesized eight phenothiazine 5,5-dioxide derivatives to directly reveal how the monomer and dimer in packing affect the RTP behavior. Dimers with strong π-π stacking (θ < 20.66°; d < 3.86 Å) lead to pure triplet excimer emission, while those with weak π-π stacking (27.02°< θ < 40.64°; 3.84 Å < d < 4.41 Å) contribute to dual RTP emissions of both monomer and triplet excimer. The valuable information of this work would promote the further development of this research field, as well as others in aggregate.

Thiazoline Carbene-Cu(I)-Amide complexes: Efficient White Electroluminescence from Combined Monomer and Excimer Emission.

Abstract: Luminescent carbene-metal-amide complexes bearing group 11 metals (Cu, Ag, Au) have recently attracted great attention due to their exceptional emission efficiency and high radiative decay rates (kr). These materials provide a less costly alternative to organic light-emitting diode (OLED) emitters based on more scarce metals, such as Ir and Pt. Herein, a series of eight Cu(I) complexes bearing as yet unexplored 1,3-thiazoline carbenes have been investigated and analyzed with respect to their light emission properties and OLED application. For the first time among the class of copper-based organometallic compounds the formation of efficient electroluminescent excimers is demonstrated. The prevalence of electroluminescence (EL) from either the monomer (bluish green) or the excimer (orange-red) can be adjusted in vacuum-deposited emissive layers by altering the extent of steric encumbrance of the emitter or its concentration. Optimized conditions in terms of the emitter structure and mass fraction allowed a simultaneous EL from the monomer and excimer, which laid the basis for a preparation of a single-emitter white OLED (WOLED) with external quantum efficiency of 16.5% and a maximum luminance of over 40000 cd m-2. Wide overlapping emission bands of the monomer and excimer ensure a device color rendering index (CRI) of above 80. In such a way the prospects of copper complexes as cost-effective materials for lighting devices are demonstrated, offering expense reduction through a cheaper emissive component and a simplified device architecture.

Ultrafast Symmetry-Breaking Charge Separation in a Perylene Bisimide Dimer Enabled by Vibronic Coupling and Breakdown of Adiabaticity.

Abstract: Perylene bisimides (PBIs) have received great attention in their applicability to optoelectronics. Especially, symmetry-breaking charge separation (SB-CS) in PBIs has been investigated to mimic the efficient light capturing and charge generation in natural light-harvesting systems. However, unlike ultrafast CS dynamics in donor-acceptor heterojunction materials, ultrafast SB-CS in a stacked homodimer has still been challenging due to excimer formation in the absence of rigidifying surroundings such as a special pair in the natural systems. Herein, we present the detailed mechanism of ultrafast photoinduced SB-CS occurring in a 1,7-bis(N-pyrrolidinyl) PBI dimer within a cyclophane. Through narrow-band and broad-band transient absorption spectroscopy, we demonstrate that ultrafast SB-CS in the dimer is enabled by the combination of (1) vibrationally coherent charge-transfer resonance-enhanced excimer formation and (2) breakdown of adiabaticity (formation of SB-CS diabats) in the excimer state via structural and solvent fluctuation. Quantum chemical calculations also underpin that the participation of strong electron-donating substituents in overall vibrational modes plays a crucial role in triggering the ultrafast SB-CS. Therefore, our work provides an alternative route to facilitate ultrafast SB-CS in PBIs and thereby establishes a novel strategy for the design of optoelectronic materials.

Pyromellitic Diimide-Extended Pillar[6]arene: Synthesis, Structure, and Its Complexation with Polycyclic Aromatic Hydrocarbons.

Abstract: A novel pyromellitic diimide-extended pillar[6]arene was synthesized in two steps with moderate yield for the first time. It showed a symmetrical stretched hexagon structure and could form 1:2 complexes with polycyclic aromatic hydrocarbons in solution. Interestingly, a linear supramolecular array between complex 1@G42 and pyrene through π···π stacking interactions was also observed in the solid state.

Exciplex-Forming Systems of Physically Mixed and Covalently Bonded Benzoyl-1H-1,2,3-Triazole and Carbazole Moieties for Solution-Processed White OLEDs

Abstract: Using the newly designed exciplex-forming 1,2,3-triazole-based acceptors with fast and efficient singlet → triplet intersystem crossing (ISC) processes, carbazole and benzoyl-1H-1,2,3-triazole derivatives were synthesized by Dimroth-type 1,2,3-triazole ring formation and Ullmann–Goldberg C–N coupling reactions. Due to the exciplex formation between covalently bonded electron-donating (carbazole) and 1,2,3-triazole-based electron-accepting moieties with small singlet-triplet splitting (0.07–0.13 eV), the compounds exhibited ISC-assisted bluish–green thermally activated delayed fluorescence. The compounds were characterized by high triplet energy levels ranging from 2.93 to 2.98 eV. The most efficient exciplex-type thermally activated delayed fluorescence was observed for ortho-substituted carbazole-benzoyl-1H-1,2,3-triazole which was selected as a host in the structure of efficient solution-processed white light-emitting diodes. The best device exhibited a maximum power efficiency of 10.7 lm/W, current efficiency of 18.4 cd/A, and quantum efficiency of 7.1%. This device also showed the highest brightness exceeding 10 thousand cd/m2. Usage of the exciplex-forming host allowed us to achieve a low turn-on voltage of 3.6 V. High-quality white electroluminescence was obtained with the close to nature white color coordinates (0.31, 0.34) and a color rendering index of 92.

Steering the multiexciton generation in slip-stacked perylene dye array via exciton coupling

Abstract: Abstract Dye arrays from dimers up to larger oligomers constitute the functional units of natural light harvesting systems as well as organic photonic and photovoltaic materials. Whilst in the past decades many photophysical studies were devoted to molecular dimers for deriving structure-property relationship to unravel the design principles for ideal optoelectronic materials, they fail to accomplish the subsequent processes of charge carrier generation or the detachment of two triplet species in singlet fission (SF). Here, we present a slip-stacked perylene bisimide trimer, which constitutes a bridge between hitherto studied dimer and solid-state materials, to investigate SF mechanisms. This work showcases multiple pathways towards the multiexciton state through direct or excimer-mediated mechanisms by depending upon interchromophoric interaction. These results suggest the comprehensive role of the exciton coupling, exciton delocalization, and excimer state to facilitate the SF process. In this regard, our observations expand the fundamental understanding the structure-property relationship in dye arrays.

π-Stacking-Dependent Vibronic Couplings Drive Excited-State Dynamics in Perylenediimide Assemblies.

Abstract: Vibronic coupling, the interplay of electronic and nuclear vibrational motion, is considered a critical mechanism in photoinduced reactions such as energy transfer, charge transfer, and singlet fission. However, our understanding of how particular vibronic couplings impact excited-state dynamics is lacking due to the limited number of experimental studies of model molecular systems. Herein, we use two-dimensional electronic spectroscopy (2DES) to launch and interrogate a range of vibronic coherences in two distinct types of perylenediimide slip stacks─along the short and long molecular axes, which form either an excimer or a mixed state between the Frenkel exciton (FE) and charge transfer states. We explore the functionality of these vibronic coherences using quantum beatmaps, which display the Fourier amplitude signal oscillations as a function of pump and probe frequencies, along with knowledge of the characteristic signatures of the FE, ionic, and excimer species. We find that a low-frequency vibrational mode of the short-axis slip stack appears concomitantly with the formation of the excimer state, survives 2-fold longer than in the FE state in the reference monomer, and shows a phase shift compared to other modes. For the long-axis slip stacks, a pair of low-frequency modes coupled to a high-frequency coordinate of the FE state were found to play a critical role in mixed-state generation. Our findings thus experimentally reveal the complex and varying roles of vibronic couplings in tightly packed multimers undergoing a range of photoinduced processes.

Excimer Formation of Perylene Bisimide Dyes within Stacking-Restrained Folda-Dimers: Insight into Anomalous Temperature Responsive Dual Fluorescence

Abstract: Open AccessCCS ChemistryRESEARCH ARTICLE6 Jun 2022Excimer Formation of Perylene Bisimide Dyes within Stacking-Restrained Folda-Dimers: Insight into Anomalous Temperature Responsive Dual Fluorescence Congdi Shang†, Gang Wang†, Yu-Chen Wei†, Qingwei Jiang, Ke Liu, Meiling Zhang, Yi-Yun Chen, Xingmao Chang, Fengyi Liu, Shiwei Yin, Pi-Tai Chou and Yu Fang Congdi Shang† College of Food Science and Engineering, Northwest A&F University, Shaanxi, Yangling 712100 Key Laboratory of Applied Surface and Colloid Chemistry of Ministry of Education, School of Chemistry and Chemical Engineering, Shaanxi Normal University, Shaanxi, Xi’an 710062 †C. Shang, G. Wang, and Y.-C. Wei contributed equally to this work.Google Scholar More articles by this author , Gang Wang† Key Laboratory of Applied Surface and Colloid Chemistry of Ministry of Education, School of Chemistry and Chemical Engineering, Shaanxi Normal University, Shaanxi, Xi’an 710062 †C. Shang, G. Wang, and Y.-C. Wei contributed equally to this work.Google Scholar More articles by this author , Yu-Chen Wei† Department of Chemistry, Taiwan University, Taipei 10617 †C. Shang, G. Wang, and Y.-C. Wei contributed equally to this work.Google Scholar More articles by this author , Qingwei Jiang Key Laboratory of Applied Surface and Colloid Chemistry of Ministry of Education, School of Chemistry and Chemical Engineering, Shaanxi Normal University, Shaanxi, Xi’an 710062 Google Scholar More articles by this author , Ke Liu Key Laboratory of Applied Surface and Colloid Chemistry of Ministry of Education, School of Chemistry and Chemical Engineering, Shaanxi Normal University, Shaanxi, Xi’an 710062 Google Scholar More articles by this author , Meiling Zhang Key Laboratory of Applied Surface and Colloid Chemistry of Ministry of Education, School of Chemistry and Chemical Engineering, Shaanxi Normal University, Shaanxi, Xi’an 710062 Google Scholar More articles by this author , Yi-Yun Chen Department of Chemistry, Taiwan University, Taipei 10617 Google Scholar More articles by this author , Xingmao Chang Key Laboratory of Applied Surface and Colloid Chemistry of Ministry of Education, School of Chemistry and Chemical Engineering, Shaanxi Normal University, Shaanxi, Xi’an 710062 Google Scholar More articles by this author , Fengyi Liu Key Laboratory of Applied Surface and Colloid Chemistry of Ministry of Education, School of Chemistry and Chemical Engineering, Shaanxi Normal University, Shaanxi, Xi’an 710062 Google Scholar More articles by this author , Shiwei Yin Key Laboratory of Applied Surface and Colloid Chemistry of Ministry of Education, School of Chemistry and Chemical Engineering, Shaanxi Normal University, Shaanxi, Xi’an 710062 Google Scholar More articles by this author , Pi-Tai Chou *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] Department of Chemistry, Taiwan University, Taipei 10617 Google Scholar More articles by this author and Yu Fang *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] Key Laboratory of Applied Surface and Colloid Chemistry of Ministry of Education, School of Chemistry and Chemical Engineering, Shaanxi Normal University, Shaanxi, Xi’an 710062 Google Scholar More articles by this author https://doi.org/10.31635/ccschem.021.202100871 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail We have fabricated a new perylene bisimide (PBI) folda-dimer ( BPBI-CB-1) by tethering two PBI moieties to the ortho-carbon positions of a carborane unit. The synthesized compound adopted distinct configurations in different solvents with dual emissions as its characteristic. The two PBI moieties in the molecule appeared either in a weakly interacted, monomer-like state or brought into close π–π contact with each other, forming an interacted stacking state. The equilibrium between these two states was governed by the nature of solvents and testing temperature. Spectroscopic and theoretical studies concluded that dual emission bands originated from intramolecular monomer-like and stacking states, respectively. Remarkably, in a solvent like 1,2-dichloroethane (DCE), both emission intensities increased with rising temperatures. The positive temperature response of the monomer emission was ascribed to an increased amount of monomer-like population, owing to its endothermic energy state, while the excimer emission was rationalized by increased population of the bright exciton state, resulting in an increased emission yield that compensated the diminished population of the stacking state. To our knowledge, this is the first report on positive temperature-responsive dual emissions associated with the synergism of intramolecular intersubunit aggregation/dissociation and excimer transformation. Download figure Download PowerPoint Introduction Exploration of the structure–functionality relationship is an eternal topic of chemical science. One of the challenging issues is the correlation among various specific configurations of a compound endowed with relatively diversified chemical/physical properties such that multifunctionality could be accessed in a single molecular unit. Driven by these issues, research endeavors on tuning photophysical properties of organic conjugated structures via configurational change have received intense attention.1–4 One popular approach is the exploitation of steric hindrance effect via anchoring bulky substituents or rigid units into molecules to increase the hindrance, stabilizing an otherwise unaffordable configuration.5–8 Meanwhile, the “rotational isomerism” is another strategy to fine-tune the configuration,9,10 in which two functional moieties are connected by a designated bridge, which could be C–C single, double, triple bonds, or even extended structures.11–15 Accordingly, mutual arrangement of the two moieties can be altered via rotation,16,17 bending,18 and structural reorganization19–21 of the bridge such that various thermally stable configurations may exist, which purportedly exhibit different properties in terms of physical or photophysical behaviors.22–25 While each of the above-mentioned approaches has been widely studied, the integration of multiple strategies into a single molecular composite, to our knowledge, has not been fully explored. In a dual moiety featured molecular dyad, the chemical nature of both functional moieties and linkers plays a crucial role in determining the configurational diversity, and hence, the associated physical and photophysical properties. In this regard, perylene bisimide (PBI) has been widely used as a functional unit to create molecular dyads. This mainly stems from its outstanding properties, such as high fluorescence quantum yield (QY), high photochemical stability, and multiple modification sites.26–29 However, PBI-based dyes are subject to dimerization and/or aggregation, which on the one hand, could extend the optoelectronic properties such as the emission Stokes shift. And on the other hand, it becomes a shortcoming when used in a monomeric state for applications such as cytometry, microscopy, sensor, photon concentrators,30–32 and so on. In fact, various covalently linked PBI dyads were reported to have face-to-face and side-by-side interactions;33–40 among these systems are the PBI molecular dimers that demonstrate rather complicated photophysical properties due to their subtle intersubunit electronic interactions in the excited state. The associated fundamental challenge has been well described by the excitonic coupling theory developed by Kasha et al.41 and extended by others.42–44 According to the theory, the interaction between the transition dipole moment vectors associated with the two fluorescent moieties causes a two-fold splitting.45–48 The relative intensities of the two absorptions depend on the mutual alignment of the respective chromophores.43 For the two transition-dipole alignments in line, one or the other of the two absorption transitions is forbidden due to accidental cancellation of the relevant transition dipole moment vectors, resulting in a non-emissive state (dark state) and a highly emissive one (bright state).49,50 The two packing alignments correspond to the well-known H- and J-type aggregates of the fluorescent dyad.51–53 Thus, ingeniously regulating the transformation of the two aggregation forms is of paramount importance in probing the structure–functionality relationship of PBIs.54–57 Herein, we created two PBI moieties, connected chemically to a carborane unit with phenylene ethynylene as linkers, which resided mutually at the ortho-carbon positions ( BPBI-CB-1; Figure 1). The designed structure is believed to separate the two PBI units at a suitable distance owing to the steric configuration of the o-carborane, endowing them with partial rotational freedom.58 The bay position modified PBI derivative was selected as the chromophore not only because of its aforementioned superior fluorescence properties but also because of its acceptable solubility in common organic solvents, avoiding the strong tendency of forming intermolecular aggregates. This design enabled us to focus mainly on the intramolecular excitonic interactions of two PBI moieties and their interplay between two different configurations (vide infra). For controls, two other carborane derivatives of PBI, namely, BPBI-CB-2 and PBI-CB-ref (Figure 1), were synthesized, which in theory, have no possibility of forming PBI aggregate intramolecularly. As a result, BPBI-CB-1 showed dual fluorescence in suitable solvents where intermolecular aggregates did not exist. Remarkably, both emission bands exhibited a positive temperature effect, which was an ultra-rare event. Comprehensive spectroscopy, dynamics, and theoretical approaches unveiled the nature of dual emissions and the origins of anomalous photophysical properties. Detailed results and relevant discussions are elaborated in the following sections. Figure 1 | The chemical structures of BPBI-CB-1, BPBI-CB-2, and PBI-CB-ref. Download figure Download PowerPoint Experimental Methods 3,4,9,10-Perylene-tetracarboxylic acid diimide was purchased from Adamas Reagent Co. Ltd. (98%; Shanghai, China). Imidazole (99%) and copper(I) iodide (98%) were purchased from Shanghai Titan Scientific Co. Ltd. (Shanghai, China). Bromine (≥97%), trimethylsilylacetylene (98%), and bis(triphenyl-phosphine)palladium(II) dichloride (98%) were purchased from TCI Shanghai (Shanghai, China). Toluene (TOL), tetrahydrofuran (THF), and diisopropylamine (DIPA) were freshly distilled from sodium benzophenone ketyl under a nitrogen atmosphere before use. Other chemicals used were of the highest grade commercially available and did not require further purification. Water used in this work was obtained from a Milli-Q reference system (Massachusetts, USA). 1H NMR, 11B NMR, and 13C NMR spectra were obtained on a Bruker AV 600 NMR spectrometer (Bruker, Karlsruhe, Germany). The high-resolution mass spectra (HRMS) were acquired in atmospheric pressure chemical ionization (APCI) sources using a Bruker maxis Ultra High Resolution Time of Flight (UHR-TOF) mass spectrometer (Bruker, Karlsruhe, Germany). Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) data were collected on a MALDI-TOF Bruker maxis mass spectrometer in electrospray ionization (ESI) positive mode (Bruker, Karlsruhe, Germany). Steady-state fluorescence excitation and emission spectra were obtained using a time-correlated single-photon counting (TCSPC) fluorescence spectrometer (FLS920; Edinburgh Instruments Ltd., Livingston, UK) with a xenon lamp as the light source at room temperature. Lifetimes were measured on the same system using an EPL-485 picosecond pulsed diode laser (Edinburgh Instruments Ltd., Livingston, UK) as the light source. The absolute fluorescence QYs were measured on the Hamamatsu C9920 (Hamamatsu Photonics K.K., Hamamatsu, Japan) Quantum Efficiency Instrument. UV–vis absorption spectra were performed on a JASCO 770V spectrometer (JASCO, Tokyo, Japan) with a spectral bandwidth of 1 nm and a scan rate of 400 nm min−1 using quartz cell cuvettes of 10 cm. The ultrafast spectroscopic studies were conducted on another TCSPC system (OB-900 L lifetime spectrometer, Edinburgh Instruments Ltd., Livingston, UK). The excitation light source at 800 nm from the Ti-Sapphire oscillator (82 MHz, Spectra-Physics, Milpitas, USA) was pulse-selected to reduce its repetition rate to typically 0.8–8 MHz and then used to generate second-harmonic (400 nm). The fluorescence was collected at a right angle with respect to the pump beam path and passed through a polarizer, which set the polarization at a magic angle (54.7°) to eliminate anisotropy. Similar data analysis and fitting procedures were compared with the previous TCSPC system were applied. The temporal resolution, after partial removal of the instrumental time broadening, was ∼20 ps. Results and Discussion As shown in Figure 1, all the title PBI derivatives contain a common component of o-carborane that was intentionally selected to direct the mutual orientations of the relevant PBI moieties, as well as to ensure solubility of the molecular system. Detailed synthesis and characterization of BPBI-CB-1 and the two references, BPBI-CB-2 and BPBI-CB-ref, are provided in Supporting Information Scheme S1 and Supporting Information Characterization Data section. To gain the basic photophysical properties of BPBI-CB-1, steady-state UV/vis absorption and fluorescence emission measurements were conducted in a wide variety of solvents ranging from less polar TOL to polar solvents like 2-methoxyethyl ether (MOE). The results depicted in Figure 2a show dual emission, specified as F1 (short wavelength, λmax ∼ 560 nm) and F2 (long wavelength, λmax ∼ 640 nm) bands with different ratiometers in different solvents, even though the spectra were recorded at a concentration as low as 2 × 10−7 mol·L−1 at room temperature. The spectra of the controls, BPBI-CB-2 and BPBI-CB-ref, in the same solvents were also recorded; the acquired spectra are shown in Supporting Information Figures S1 and S2, respectively. Based on the comprehensive solvent-dependent studies (for details, see the Supporting Information), we found that in 1,1,2,2-tetrachloroethane (TCE) and 1,2-dichloroethane (DCE), the target compound BPBI-CB-1 demonstrated unique solvent-dependent dual emission behaviors; therefore, these two solvents were chosen for conducting further research to explore the structure-functionality relationship. To ascertain the intramolecular effect of the origin of the observed dual emission of BPBI-CB-1 in the examined solvents, concentration-dependent fluorescence spectra of the ensemble in TCE and DCE were recorded at room temperature, as shown in Figures 2b and 2c, respectively. We explored the boundary between intramolecular intersubunit aggregation and intermolecular aggregation by plotting the intensity ratio for F2 versus F1 bands against the PBI derivatives concentration. The gradients of the two plots depicted in the insets of Figures 2b and 2c results from a drastic change in concentrations from 1 × 10−6 to 4 × 10−7 mol·L−1, respectively. The ratio of the dual emission remains constant at lower concentrations (2 × 10−7 mol·L−1), revealing that the dual emissions were authentic in the dilute solution where the intermolecular BPBI-CB-1 interaction, and hence, the associated emission had been eliminated. These results indicated the existence of intramolecular interaction, intrinsically, between two PBI units in BPBI-CB-1, giving the anomalous dual emission. Figure 2 | The absorption and fluorescence emission spectra (λex = 470 nm) of BPBI-CB-1 in different solvents, recorded at a concentration of 2 × 10−7 mol·L−1 at room temperature (a). The fluorescence emission spectra (λex = 470 nm) of BPBI-CB-1, recorded at different concentrations in TCE (b) and DCE (c) at room temperature; the insets are the plots of ratios of emission bands with changes in concentration. Note: TCM, trichloromethane, DMF, dimethyl-formamide. Download figure Download PowerPoint To gain further insights into the photophysical behavior, the absorption/excitation and emission spectra of BPBI-CB-1, BPBI-CB-2, and BPBI-CB-ref in TCE and/or DCE were recorded at a concentration of ∼2 × 10−7 mol·L−1; the results are depicted in Figures 3a–3d. As expected, PBI-CB-ref, which represented the prototypical PBI monomer property, was characterized by a structural emission band (the F1 band) consisting of two prominent vibronic progressive peaks at ∼540 and 590 nm and a shoulder in the longer wavelength side (Figure 3a). This spectral feature was ascribed to a typical monomer-relevant emission of the PBI derivatives. In comparison, the emission spectrum of BPBI-CB-2 (Figure 3b) resembled that of PBI-CB-ref, possessing the vibronic peaks at 560 and 610 nm, which unambiguously resulted from the derivatized PBI monomer emission, without any sign of the F2 emission band originating from the intra-PBI aggregate. Thus, the monomeric emission nature of BPBI-CB-2 in the solution ruled out the possibility of both intermolecular and intramolecular aggregation. Figure 3 | The absorption and fluorescence excitation and emission spectra of PBI-CB-ref (a) and BPBI-CB-2 (b) in TCE, recorded at a concentration of 5 × 10−7 mol·L−1 and at room temperature (λex = 470 nm). The absorption and fluorescence excitation and emission spectra of BPBI-CB-1 in TCE (c) and DCE (d), recorded at a concentration of 2 × 10−7 mol·L−1 at room temperature (λex = 470 nm). Download figure Download PowerPoint Detailed monomer behavior for PBI-CB-ref and BPBI-CB-2 was also provided by their associated absorption spectra ( Supporting Information Figures S1 and S2). The absorption bands of PBI-CB-ref at ∼550 and ∼500 nm (Figure 3a) corresponded to the 0–0 and 0–1 absorption transitions from the ground singlet state (S0) to the first excited singlet state (S1), respectively, attributed to a vibronic coupling between the electronic transition and C–C-stretching modes of the perylene core of PBI moiety. The large ratio (∼1.50) of the two vibronic absorption transitions (A0–0/A0–1) for BPBI-CB-ref revealed the monomer nature of PBI.22 Similar elucidation is also applicable for the absorption of PBI-CB-2 where the ratio for 0–0 (∼530 nm) versus 0–1 (∼490 nm), that is, A0–0/A0–1, was calculated to be 1.52, which was within the category of the monomer behavior. The excitation spectra profiles of both PBI-CB-ref and PBI-CB-2 ( Figures 3a and 3b), independent of the monitored emission wavelength, were identical and the same as the absorption profile, further confirming the monomolecular feature of both compounds. This result is taken for granted for PBI-CB-ref because it possesses only one PBI unit. As for BPBI-CB-2, the result is not difficult to apprehend by considering that the dual PBI units were far away from each other, according to the structure depicted in Figure 1. Therefore, in sufficiently diluted solution, both intra- and inter-PBI interactions could be eliminated. The monomeric behavior led to high fluorescence QY (>80%) for both BPBI-CB-2 and PBI-CB-ref in solution. In stark contrast, as shown in Figure 3c, PBI-CB-1 dissolved in TCE revealed a significantly decreased absorbance A0–0/A0–1 ratio of ∼1.18 (cf. 1.52 in BPBI-CB-2). Since the concentration was well below the threshold for forming intermolecular aggregation (vide supra), the results manifested intramolecular interaction of the two PBI units in PBI-CB-1. The corresponding emission (Figure 3c) of PBI-CB-1 showed a more pronounced effect regarding the intramolecular interaction, which, except for the two prominent vibronic peaks (∼570 and ∼615 nm), associated with the monomer PBI unit (the F1 band); the longer wavelength F2 band was non-negligible, broad, structureless, and most plausibly, ascribed to the presence of an intramolecular excimer induced by intra-PBI aggregation. Such intramolecular PBI–PBI interaction became more enhanced when PBI-CB-1 was dissolved in DCE (Figure 3d), supported by the decreased intensity ratio (A0–0/A0–1) for the absorption bands of PBI-CB-1 from 1.18 in TCE to 0.78 in DCE, pointing out to stronger intrasubunit interaction of the two PBI units. This is further indisputably verified by the corresponding emission spectra in DCE, consisting of a strong, dominant, and long-wavelength F2 emission maximized at 650 nm, while the F1 emission at ∼560 nm became minimized. Thus, the F1 and F2 emission bands were reasonably ascribed to the PBI monomer and PBI-associated excimer emission, respectively. Undoubtedly, the behavior of the dual PBI units of BPBI-CB-1 was distinct from the dual PBI units of BPBI-CB-2. While the two PBI-subunits have negligible interaction in BPBI-CB-2, BPBI-CB-1 tended to allow intramolecular excimer formation via the interaction of the two PBI-subunits. Moreover, closer inspection of the excitation spectra monitoring at F1 (e.g., 570 nm) and F2 (e.g., 650 nm) bands for BPBI-CB-1 (Figures 3c and 3d) produced a slightly different spectral feature in which the former revealed a profile similar to regular monomer absorption, with A0–0/A0–1 ratio of ∼1.52. The latter showed an A0–0/A0–1 ratio of ∼1.20 that supported the intrasubunit PBI interaction. Thus, unambiguously, there existed two types of ground-state species for BPBI-CB-1 in DCE (and TCE), consisting of one configuration where two PBI subunits were in an orientation/distance that has negligible interaction, giving PBI a monomer-like emission and another configuration where two PBI subunits were in an orientation/distance that was slightly coupled, giving excimer emission upon excitation. For the clarity of discussion, these two conformers were denoted as intra-PBI monomer and intra-PBI aggregate, which are in equilibrium in the ground state. Notably, the results also demonstrated that the PBI moieties of BPBI-CB-1 showed much more pronounced excimer emission in DCE than in TCE. The difference in ratiometric emission between two solvents reflected different degrees of equilibrium between intra-PBI monomer and intra-PBI aggregate in these two solvents, though the corresponding structures have not yet been disclosed (vide infra). The changes in equilibrium could be fine-tuned by mixing TCE and DCE solvents; the results showed that the monomer dominated the absorption and emission recorded in pure TCE, which gradually changed to dimer or excimer dominated absorption and emission in pure DCE with an increasing volume ratio of the latter (see Supporting Information Figures S3 and S4). For further exploration, we carried out temperature-dependent fluorescence measurements of the titled compounds in two solutions (DCE and TCE). To our surprise, both F1 and F2 emission intensity of BPBI-CB-1 in DCE increased significantly upon raising the temperature from 253 to 343 K (Figure 4a). In other words, both intensities of F1 and F2 showed positive temperature responsiveness, suggesting that at high temperatures, the population of the intramolecular PBI aggregates rose from the less-emissive state to the bright state. This statement was further supported by the temperature independence of population decay lifetimes for both F1 and F2 emissions ( Supporting Information Figure S5). BPBI-CB-1 in TCE revealed a similar effect in the same temperature range, but the changes were relatively small and became irregular at certain temperatures (Figure 4b). For comparison, the fluorescence spectra of the two reference compounds, BPBI-CB-2 and BPBI-CB-ref, in the two solvents were also recorded at different temperatures. Note that the experiment was performed under a diluted concentration of 5 × 10−7 mol·L−1 to eliminate the aggregation effect. The results presented in Supporting Information Figures S6 and S7 for BPBI-CB-2 and BPBI-CB-ref, respectively, showed no noticeable temperature-dependent emission behavior in the two solvents. Figure 4 | Fluorescence emission spectra of BPBI-CB-1 in DCE (a) and TCE (b), recorded at different temperatures at a concentration of 2 × 10−7 mol·L−1 (λex = 470 nm). Download figure Download PowerPoint Repetitive tests have been performed in the BPBI-CB-1/DCE system. The results shown in Supporting Information Figure S8 revealed that the positive temperature responsiveness of the emission intensity is fully reversible, affirming temperature-dependent changes in equilibrium rather than any irreversible chemical process. Further support is given by the temperature-dependent absorption measurements of BPBI-CB-1 in DCE ( Supporting Information Figure S9), where the spectra showed isosbestic points at ∼530 nm and ∼550 nm, concluding the existence of an equilibrium between two species, viz, the proposed intra-PBI monomer and intra-PBI aggregate. Moreover, upon increasing temperature from 298 K to 343 K, the intensity ratio between A0-0 and A0-1 rose from 0.75 to 0.80, indicating an increase in intra-PBI monomer species, and hence, an enhanced dissociation of the intra-PBI aggregate at a higher temperature. This could well be explained by the thermodynamic relationship, as follows59: intra − PBI monomer ↔ intra − PBI aggregate (1) ln K e q = − Δ H ! R T + Δ S ! R (2)where Δ H ! and, respectively, Δ S ! are the standard enthalpy and entropy changes of the concerned process, and Keq denotes the equilibrium constant between intra-PBI monomer and intra-PBI aggregate. Thermodynamically, upon increasing temperature, the exothermic reaction (negative Δ H ! ) from intra-PBI monomer to intra-PBI aggregate led to an increase of the intra-PBI monomer population (eq. 2), rationalizing the positive temperature responsiveness of the monomer emission. However, the decrease of the PBI aggregate was accompanied by an increase in PBI excimer emission, contrary to the conventional expectation. We intend to rationalize this anomalous observation later, after performing both time-resolved spectroscopic and computational approaches, elaborated as follows: The time-resolved fluorescence decays of BPBI-CB-1 in DCE were monitored at 530 and 690 nm, mainly dominated by typical monomer and excimer emissions of the PBI units, respectively (Figures 2 and 3). Upon 400 nm excitation and monitoring at 530 nm for the monomer emission (Figure 5), there appeared a fast decay component of 250 ps and a much slower population decay component of 6.6 ns (Table 1). Contrarily, the excimer emission monitored at 690 nm consisted of a fast rise component of 168 ps, accompanied by a long population decay time of 17 ns. Significantly, the fast 250 ps decay of the monomer emission, within the experimental uncertainty, correlated well with the rise lifetime (168 ps) of the excimer emission, supporting a precursor–successor type of kinetic relationship. In other words, it took ∼168–250 ps time constant for the excimer formation. Comparing with the results monitored at 530 nm, the relatively faster rise lifetime and the smaller pre-exponential factor at 690 nm were engendered by the interference of the decay signals from the F1 emission band. However, the differences in the slow population decay lifetimes of the monomer (6.6 ns) and excimer (17 ns) revealed a nonequilibrium characteristic in the transition between these two excited states. This result is consistent with the conclusion made from the steady-state observation, showing the existence of two types of BPBI-CB-1 configuration in DCE, the intra-PBI monomer and intra-PBI aggregate, denoted as BPBI-CB-1-M (M) and PBI-CB-1-M ( D), respectively. The absorption spectra of M and D were somewhat similar, except for the ratiometric difference in vibronic absorption peaks due to the PBI-PBI interaction in D. For example, the excitation of the M configuration at 400 nm gives a monomer-like emission, maximized at 560 nm with a population decay time of 6.6 ns. Similar excitation (400 nm) for D rendered a fast decay (168–250 ps) of the monomer-like species, which mainly underwent excimer formation, giving rise to an excimer emission with a rise and decay time of 220–250 ps and 17 ns, respectively. Note that such an excimer formation kinetics is relatively slow compared to other singlet excited-state electronic transition such as photointroduced intramo

Real‐time Observation of Structural Dynamics Triggering Excimer Formation in a Perylene Bisimide Folda‐dimer by Ultrafast Time‐Domain Raman Spectroscopy

Abstract: In π-conjugated organic photovoltaic materials, an excimer state has been generally regarded as a trap state which hinders efficient excitation energy transport. But despite wide investigations of the excimer for overcoming the undesirable energy loss, the understanding of the relationship between the structure of the excimer in stacked organic compounds and its properties remains elusive. Here, we present the landscape of structural dynamics from the excimer formation to its relaxation in a co-facially stacked archetypical perylene bisimide folda-dimer using ultrafast time-domain Raman spectroscopy. We directly captured vibrational snapshots illustrating the ultrafast structural evolution triggering the excimer formation along the interchromophore coordinate on the complex excited-state potential surfaces and following evolution into a relaxed excimer state. Not only does this work showcase the ultrafast structural dynamics necessary for the excimer formation and control of excimer characteristics but also provides important criteria for designing the π-conjugated organic molecules.

Excimer Formation Inhibits the Intramolecular Singlet Fission Dynamics: Systematic Tilting of Pentacene Dimers by Linking Positions.

Abstract: The role of excimer formation in inhibiting or enhancing the efficiency of the intramolecular singlet fission (iSF) process has been a subject of recent debate. Here, we investigated the effect of excimer formation on iSF dynamics by modifying its configuration by connecting pentacenes at various positions. Hence, pentacene dimers having slip-stacked (2,2' BP, J-type), oblique (2,6' BP), and facial (6,6' BP, H-type) configurations were synthesized by covalently linking pentacenes at positions 2,2', 2,6', and 6,6', respectively, with an ethynyl bridge, and their ultrafast excited-state relaxation dynamics were characterized. Femtosecond time-resolved transient absorption spectra revealed that the efficiency of iSF dynamics decreased from slip-stacked (182%) to oblique configuration (97%),whereas in the 6,6' BP with facial configuration, strong electronic coupling led to the formation of excimers that decayed nonradiatively without formation of correlated triplet pairs. These studies reveal the formation of excimers by strong intrapentacene electronic coupling upon ultrafast excitation, preventing the efficient iSF process.

Deep-Red Electro-fluorescent based on an Excimer Emission with Hot-Exciton Channels

Abstract: Red and deep-red fluorescent materials are broadly applied in many fields such as organic light emitting diodes (OLEDs), biological imaging and night-vision devices. In this work, we designed and synthesized...

FAP-α-Instructed Coumarin Excimer Formation for High Contrast Fluorescence Imaging of Tumor.

Abstract: Emissive excimers, which are formed by planar polycyclic aromatic fluorophores (e.g., coumarin), enable high contrast tumor imaging. However, it is still challenging to "turn on" excimer fluorescence in physiological dilute solutions. The biocompatible CBT-Cys click condensation reaction enables both intra- and intermolecular aggregations of the as-loaded fluorophores on the probe molecules, which may promote the generation of emissive excimers in a synergistic manner. As a proof-of-concept, we herein design a fluorescence probe Cbz-Gly-Pro-Cys(StBu)-Lys(coumarin)-CBT (Cbz-GPC(StBu)K(Cou)-CBT), which can be activated by FAP-α under tumor-inherent reduction conditions, undergo a CBT-Cys click reaction, and self-assemble into coumarin nanoparticle Cou-CBT-NP to "turn on" the excimer fluorescence. In vitro and in vivo studies validate that this "smart" probe realizes efficient excimer fluorescence imaging of FAP-α-overexpressed tumor cells with high contrast and enhanced accumulation, respectively. We anticipate that this probe can be applied for diagnosis of FAP-α-related diseases in the clinic in near future.

Dynamically stable and amplified circularly polarized excimer emission regulated by solvation of chiral co-assembly process

Abstract: Abstract Chiral supramolecular assembly has been assigned to be one of the most favorable strategies for the development of excellent circularly polarized luminescent (CPL)-active materials. Herein, we report our study of an achiral boron-containing pyrene (Py)-based chromophore (PyBO) as a circularly polarized excimer emission (CPEE) dye induced by chiral co-assemblies containing chiral binaphthyl-based enantiomers ( R / S -M). Chiral co-assembly R / S -M-(PyBO) 4 fresh film spin-coated from toluene solution can exhibit orderly nanofibers and strong green CPEE (λ em = 512 nm, g em = ±0.45, Φ FL = 51.2 %) resulting from an achiral PyBO excimer. In contrast, only a very weak blue CPL was observed (λ em = 461 nm, g em = ± 0.0125, Φ FL = 19.0 %) after 187 h due to PyBO monomer emission as spherulite growth. Interestingly, this kind of chiral co-assembly R -M-(PyBO) 4 -T film from tetrahydrofuran (THF) solution retains uniform morphology and affords the most stable and strongest CPEE performance (λ em = 512 nm, g em = + 0.62, Φ FL = 53.3 %) after 10 days.

Highly stable and efficient deep-red phosphorescent organic light-emitting devices using a phenanthroline derivative as an n-type exciplex host partner

Abstract: A new entry of nBPhen-based n-type exciplex host partner realizes high efficiency and highly stable deep red phosphorescent organic light-emitting devices with an emission peak wavelength of 670 nm, and maximum external quantum efficiency of 17%.

Tunable Excimer Circularly Polarized Luminescence in Isohexide Derivatives from Renewable Resources

Abstract: Abstract Organic compounds showing circularly polarized luminescence (CPL) are at the forefront of novel applications and technologies. Here we show the synthesis and chiroptical properties of pyrene and perylene derivatives of inexpensive chiral scaffolds: isomannide and isosorbide. Low‐intensity ECD spectra were obtained, suggesting the absence of chromophore interaction in the ground state, except in the case of isomannide bis‐perylenecarboxylate, whose ECD spectrum showed a positive exciton couplet. All isomannide derivatives, with the only exception of the one containing a pyrenecarboxylate and a perylenecarboxylate, exhibited excimer CPL spectra, whereas isosorbide derivatives did not show any CPL. Isomannide derivatives bearing two pyrenecarboxylate or two pyrenylacetate groups showed positive CPL emission with dissymmetry factors up to 10−2, which depends on the conformational freedom of the appended units. The CPL sign, Stokes shift and order of magnitude of dissymmetry factor were reproduced by excited‐state calculations on a representative compound. Interestingly, the mixed derivative containing pyrenic units with different spacing from the isomannide scaffold showed an oppositely signed excimer band with respect to the homo‐substituted derivatives.

Excimer Formation in the Non‐Van‐Der‐Waals 2D Semiconductor Bi2O2Se

Abstract: The layered semiconductor Bi2O2Se is a promising new‐type 2D material that holds layered structure via electrostatic forces instead of van der Waals (vdW) attractions. Aside from the huge success in device performance, the non‐vdW nature in Bi2O2Se with a built‐in interlayer electric field has also provided an appealing platform for investigating unique photoexcited carrier dynamics. Here, experimental evidence for the observation of excimers in multilayer Bi2O2Se nanosheets via transient absorption spectroscopy is presented. It is found that the excimer formation is the primary decay pathway of photoexcited excitons and three‐stage excimer dynamics with corresponding time scales are established. Excitation‐fluence‐dependent excimer dynamics further suggest that the excimer is diffusive and its formation can be simply described as excitons relaxed to an excimer geometry. This work indicates the outstanding promise of unique excitonic processes in Bi2O2Se, which may motivate novel device designs.

Noncovalently bound excited-state dimers: a perspective on current time-dependent density functional theory approaches applied to aromatic excimer models

Abstract: Excimers are supramolecular systems whose binding strength is influenced by many factors that are ongoing challenges for computational methods, such as charge transfer, exciton coupling, and London dispersion interactions. Treating the various intricacies of excimer binding at an adequate level is expected to be particularly challenging for Time-Dependent Density Functional Theory (TD-DFT) methods. In addition to well-known limitations for some TD-DFT methods in the description of charge transfer or exciton coupling, the inherent London dispersion problem from ground-state DFT translates to TD-DFT. While techniques to appropriately treat dispersion in DFT are well-developed for electronic ground states, these dispersion corrections remain largely untested for excited states. Herein, we aim to shed light on current TD-DFT methods, including some of the newest developments. The binding of four model excimers is studied across nine density functionals with and without the application of additive dispersion corrections against a wave function reference of SCS-CC2/CBS(3,4) quality, which approximates select CCSDR(3)/CBS data adequately. To our knowledge, this is the first study that presents single-reference wave function dissociation curves at the complete basis set level for the assessed model systems. It is also the first time range-separated double-hybrid density functionals are applied to excimers. In fact, those functionals turn out to be the most promising for the description of excimer binding followed by global double hybrids. Range-separated and global hybrids—particularly with large fractions of Fock exchange—are outperformed by double hybrids and yield worse dissociation energies and inter-molecular equilibrium distances. The deviation between each assessed functional and reference increases with system size, most likely due to missing dispersion interactions. Additive dispersion corrections of the DFT-D3(BJ) and DFT-D4 types reduce the average errors for TD-DFT methods but do so inconsistently and therefore do not offer a black-box solution in their ground-state parametrised form. The lack of appropriate description of dispersion effects for TD-DFT methods is likely hindering the practical application of the herein identified more efficient methods. Dispersion corrections parametrised for excited states appear to be an important next step to improve the applicability of TD-DFT methods and we hope that our work assists with the future development of such corrections.