Showing papers on "Excimer published in 2014"
TL;DR: The synthesis and characterization of two PDI dimers in which the chromophores are covalently linked by a redox-inactive triptycene bridge in orientations that are cofacial and slip-stacked along their N-N axes are reported.
Abstract: Excitation energy transfer in perylene-3,4:9,10-bis(dicarboximide) (PDI) aggregates is of interest for light-harvesting applications of this strongly absorbing and π–π stacking chromophore. Here we report the synthesis and characterization of two PDI dimers in which the chromophores are covalently linked by a redox-inactive triptycene bridge in orientations that are cofacial (1) and slip-stacked along their N–N axes (2). Femtosecond transient absorption experiments on 1 and 2 reveal rapid exciton delocalization resulting excimer formation. Cofacial π–π stacked dimer 1 forms a low-energy excimer state absorption (λmax = 1666 nm) in τ = ∼2 ps after photoexcitation. Inserting a phenyl spacer on the bridge to generate a slip-stacked PDI–PDI geometry in 2 results in a less stable excimer state (λmax = 1430 nm), which forms in τ = ∼12 ps due to decreased electronic coupling. The near-infrared (NIR) excimer absorption of cofacial dimer 1 is ∼120 meV lower in energy than that of slip-stacked dimer 2, further highlighting electronic differences between these states.
153 citations
TL;DR: The Sonogashira coupling of γ-CD-encapsulated alkynylpyrenes with terphenyl-type stopper molecules gave a doubly alkynypyrene-threaded [4]rotaxane, which showed strong circularly polarized luminescence and may result from the two stacked pyrenes existing in the rotaxane in an asymmetrically twisted manner.
Abstract: The Sonogashira coupling of γ-CD-encapsulated alkynylpyrenes with terphenyl-type stopper molecules gave a doubly alkynylpyrene-threaded [4]rotaxane. The rotaxane showed only excimer emission, with a high fluorescence quantum yield of Φf=0.37, arising from the spatially restricted excimer within the cavity of the γ-CD. The excimer emission suffered little from self-quenching up to a concentration of 1.5×10−5 M and was circularly polarized with a high glum value of −1.5×10−2. The strong circularly polarized luminescence may result from the two stacked pyrenes existing in the rotaxane in an asymmetrically twisted manner.
151 citations
TL;DR: Femtosecond near-infrared transient absorption experiments reveal a unique low-energy transition that can be used to identify and characterize this state without overlapping excited singlet-state absorption.
Abstract: Energy transfer in perylene-3,4:9,10-bis(dicarboximide) (PDI) aggregates is often limited by formation of a low-energy excimer state. Formation dynamics of excimer states are often characterized by line shape changes and peak shift dynamics in femtosecond visible transient absorption spectra. Femtosecond near-infrared transient absorption experiments reveal a unique low-energy transition that can be used to identify and characterize this state without overlapping excited singlet-state absorption. Three covalently bound PDI dimers with differing PDI-PDI distances were studied to probe the influence of interchromophore electronic coupling on the PDI excimer transient spectra and dynamics.
150 citations
TL;DR: A thorough spectroscopic investigation on the exciton relaxation pathways, including excimer formation, in a perylene-3,4:9,10-bis(dicarboximide) (PBI) dimer aggregate 1 by using time-resolved fluorescence and transient absorption spectroscopy combined with excitation-power and polarization dependence.
Abstract: Although it is commonly known that H-type PBI aggregates give rise to a broad, red-shifted excimer fluorescence with considerably longer fluorescence lifetimes than observed for the monomers, the underlying mechanisms of excimer formation and other relevant exciton dynamics in such π-stacked systems are still far from being understood. In this context, we demonstrate a thorough spectroscopic investigation on the exciton relaxation pathways, including excimer formation, in a perylene-3,4:9,10-bis(dicarboximide) (PBI) dimer aggregate 1 by using time-resolved fluorescence and transient absorption spectroscopy combined with excitation-power and polarization dependence. It was found that the excited dimer formation process followed by structural rearrangement is approximately two times faster than observed within larger PBI aggregates. Excitation-power-dependent transient absorption decay profiles revealed the fully delocalized nature of excitons in the dimer as opposed to larger stacks.
129 citations
TL;DR: In this paper, a series of tetradentate platinum complexes that exhibit both efficient monomer and excimer emission energy can be separately tuned via small modifications to the cyclometalating ligands, enabling the fabrication of single, doped, white organic light-emitting diodes with long operational lifetime.
Abstract: A series of tetradentate platinum complexes that exhibit both efficient monomer and excimer emission are synthesized. Via small modifications to the cyclometalating ligands, both the monomer and excimer emission energy can be separately tuned. Devices employing all of the developed emitters demonstrate impressively high external quantum efficiencies (EQEs) within the range of 22% to 27% for concentrations between 2% and 16%. The halogen-free design of the complexes also enables the fabrication of single, doped, white organic light-emitting diodes (OLEDs) with long operational lifetimes. A balanced white device employing the complex Pt2O2, achieves a device operational lifetime to 80% of the initial luminance estimated at over 200 h at 1000 cd m–2, while also achieving 12.5% peak EQE for a warm white light with a color rendering index of 80. Furthermore, a highly doped device exhibiting nearly exclusive excimer emission showed an impressive operational lifetime, which is estimated at more than 400 h for 1000 cd m-2.
109 citations
TL;DR: Simple, sensitive, selective, and inexpensive sensing of DNA methylation was established and perylene probe monomer-excimer transition signal could be detected.
Abstract: A new label-free strategy for sensitive fluorometric biosensing based on perylene probe monomer–excimer transition has been developed. A negatively charged perylene probe (compound 1) was used. Compound 1 shows strong monomer fluorescence in an aqueous buffer solution. A cationic polymer could induce aggregation of compound 1 through noncovalent interactions. Compound 1 monomer emission was quenched, and meanwhile strong excimer emission was observed. Upon addition of a single-stranded DNA (an anionic polymer), strong electrostatic attractive interactions between the cationic polymer and the DNA weakened the binding of aggregates of compound 1 to the polycation. Compound 1 monomers were released, and excimer–monomer emission transition was detected. This observation formed the basis for DNA methyltransferase (MTase) activity detection. When the 3′-OH terminus of a duplex DNA was removed, the DNA strands could not be elongated by terminal deoxynucleotidyl transferase (TdT), and little restoration of compou...
70 citations
TL;DR: Fluorescence quenching of the mesoporous thin films with bright pyrene excimer emission can be easily observed under UV light, enabling the naked-eye detection of nitro-explosives and the films can be reused at least five times.
Abstract: We report the preparation of mesoporous thin films with bright pyrene excimer emission and their application in visual and rapid detection of nitroaromatic explosive vapors. The fluorescent films were produced by physically encapsulating pyrene molecules in the organically modified silica (ormosil) networks which were prepared via a facile template-free sol–gel method. Formation and stability of pyrene excimer emission were investigated in both porous and nonporous ormosil thin films. Excimer emission was significantly brighter and excimer formation ability was more stable in porous films compared to nonporous films. Rapid and selective quenching was observed in the excimer emission against vapors of nitroaromatic molecules; trinitrotoluene (TNT), dinitrotoluene (DNT), and nitrobenzene (NB). Fluorescence quenching of the films can be easily observed under UV light, enabling the naked-eye detection of nitro-explosives. Furthermore, excimer emission signal can be recovered after quenching and the films can ...
67 citations
TL;DR: A new pyrene pyridine conjugate (PPC) has been developed as a selective fluorescent sensor for Ag+ ion that exhibits high selectivity and sensitivity toward Ag+ as fluorescence ‘on–off’ behaviour in HEPES-buffered DMSO–H2O solution.
Abstract: A new pyrene pyridine conjugate (PPC) has been developed as a selective fluorescent sensor for Ag+ ion. Probe PPC exhibits high selectivity and sensitivity toward Ag+ as fluorescence ‘on–off’ behaviour in HEPES-buffered DMSO–H2O (1 : 1, (v/v) HEPES = 50 mM, pH = 7.4) solution with a detection limit of 0.29 × 10−8 M−1. The turn-off fluorescence sensing of the Ag+ ion occurs through dual pathways, i.e. changes and alternations in the photophysical properties. The binding of Ag+ ion prevents excimer formation and also induces intramolecular photoinduced electron transfer (PET) from the pyridine–Ag+ ion bound receptor to pyrene because of structural rigidification, which quenches excimer and monomer emissions with a butterfly-like skeleton.
47 citations
TL;DR: In this article, 1,8-Naphthalimides (NI) aggregate in both extremely polar and nonpolar solvents and the aggregation induced emission of NIs is attributed to the intermolecular excimer and/or the intramolecular exiplex formation.
Abstract: 1,8-Naphthalimides (NI) aggregate in both extremely polar and nonpolar solvents. The aggregation induced emission of NIs is attributed to the intermolecular excimer and/or the intramolecular exciplex formation.
41 citations
TL;DR: White emission with two sharp strong peaks was obtained by introducing a terphenyl group into a highly twisted core chromophore, which promoted a molecular orientation in the film state suitable for excimer formation.
39 citations
TL;DR: The luminescence properties and color tuning of [Pt(dpb)Cl] (dpbH=1,3-di(2-pyridyl)benzene) and its analogues are investigated and the formation of the excimer and the excited trimer were concluded to be exothermic processes.
Abstract: We investigated the luminescence properties and color tuning of [Pt(dpb)Cl] (dpbH=1,3-di(2-pyridyl)benzene) and its analogues. An almost blue emission was obtained for the complex [Pt(Fmdpb)CN] (FmdpbH=4-fluoro-1,3-di(4-methyl-2-pyridyl)benzene), modified by the introduction of F and CH3 groups to the dpb ligand and the substitution of Cl by CN. As the concentration of the solution was increased, the color of the emission varied from blue to white to orange. The color change resulted from a monomer-excimer equilibrium in the excited state. A broad emission spectrum around 620 nm was clearly detected along with a structured monomer emission around 500 nm. Upon further increases in concentration, another broad peak appeared in the longer wavelength region of the spectrum. We assigned the near-infrared band to the emission from an excited trimer generated by the reaction of the excimer with the ground-state monomer. The emission lifetimes of the monomer, dimer, and trimer were evaluated as τM =12.8 μs, τD =2.13 μs, and τT =0.68 μs, respectively, which were sufficiently long to allow association with another Pt(II) complex and dissociation into a lower order aggregate. Based on equilibrium constants determined from a kinetic study, the formation of the excimer and the excited trimer were concluded to be exothermic processes, with ΔG*D =-24.5 kJ mol(-1) and ΔG*T =-20.4 kJ mol(-1) respectively, at 300 K.
TL;DR: The singlet fission induced by two-photon and consecutive two-quantum absorption is reported for the first time in an α-perylene crystal.
Abstract: Excited-state dynamics in α-perylene single crystals is studied by time-resolved fluorescence and transient absorption techniques under different excitation conditions. The ultrafast lifetimes of the "hot" excimer (Y) state were resolved. Three competing excited-states decay channels are observed: excimer formation, dimer cation generation, and singlet fission. The singlet fission induced by two-photon and consecutive two-quantum absorption is reported for the first time in an α-perylene crystal.
TL;DR: This work provides the first atomistic description of the processes triggered by the absorption of UV light, reproducing and assigning the experimental optical and electronic circular dichroism spectra.
Abstract: Herein, a full quantum mechanical study, in solution, of several models of guanine-quadruplex helices, both parallel and antiparallel, containing up to eight guanine residues, in their electronic excited state is reported By exploiting TD-DFT calculations and including solvent effects by the polarizable continuum model, we provide the first atomistic description of the processes triggered by the absorption of UV light, reproducing and assigning the experimental optical and electronic circular dichroism spectra The absorbing excited states are delocalized over multiple bases, whereas emission involves a stacked guanine dimer or a monomer Several states, with a varying degree of localization and charge-transfer character, rule the photoexcited dynamics, which are deeply affected by the quadruplex topology The lowest excited-state minimum for parallel quadruplex is an asymmetric excimer involving two stacked guanines, with a small charge transfer character, whereas for the anti-parallel structure, with the same topology of the thrombin binding aptamer, it is a fully symmetric excimer, characterized by a strong decrease of the stacking distance A monomer-like decay path is the most relevant nonradiative decay pathway Insights on the effect of the ions (K+ or Na+) on the excited state decay are also provided
TL;DR: A hexakis(pyrenyloxy)cyclotriphosphazene is synthesized by the reaction of N3P3Cl6 with 2-hydroxypyrene, and its excimer emission through intramolecular interactions in solution and in the solid state has been investigated by fluorescence spectroscopy and X-ray crystallography.
Abstract: A hexakis(pyrenyloxy)cyclotriphosphazene is synthesized by the reaction of N3P3Cl6 with 2-hydroxypyrene, and its excimer emission through intramolecular interactions in solution and in the solid state has been investigated by fluorescence spectroscopy and X-ray crystallography. Thermal and electrochemical properties were investigated. A DFT benchmark study has been performed to evaluate the intramolecular interactions and molecular orbital levels by comparing with the experimental results.
TL;DR: The fluorescent spectra in combination with gas response behavior of acrylic polymers doped with dibenzoyl(methanato)boron difluoride (DBMBF2) were studied and the role of acrylic matrix polarity upon the fluorescence spectra and fluorescence lifetime was analyzed.
Abstract: The fluorescent spectra in combination with gas response behavior of acrylic polymers doped with dibenzoyl(methanato)boron difluoride (DBMBF2) were studied by fluorescence spectroscopy and time-resolved fluorescence lifetime. The role of acrylic matrix polarity upon the fluorescence spectra and fluorescence lifetime was analyzed. Changes in emission of the dye doped polymers under exposure to toluene, n-hexane and ethanol were monitored. The fluorescence lifetimes were measured for the singlet excited state as well as the exciplex formed between DBMBF2 and toluene. A reduction of the transition energy to the first singlet-excited state in the four polymers was observed, compared to solution. Reversible exciplex formation, viz. a red shifted fluorescence emission was perceived when exposing the polymers to toluene, while for hexane and ethanol only reversible reduction of the fluorescence occurred. Longer singlet and shorter exciplex lifetimes were observed for non-polar matrixes. The latter mechanism is explained in function of the lower charge transfer character of the exciplex in non-polar matrixes. Additionally, the quantum yield of the dye in the polymer matrix increased almost seventh-fold compared to values for solution.
TL;DR: ES-1 provided a novel fluorescence assay based on excimer-monomer switch of N-aryl-1,8-naphthalimide to quantitatively measure F(-) with a detection limit of 0.133 ppm.
Abstract: A N-aryl-1,8-naphthalimide based sensor (ES-1) bearing a trimethylsilyl ether has been synthesized by a two-step reaction for quantitative detection of fluoride (F−). ES-1 exhibited monomer/excimer emissions at 410 and 524 nm respectively in CH2Cl2. In the presence of F−, the desilylation of trimethylsilyl ether caused decay of the excimer emission as well as enhancement of the monomer emission to give a ratiometric signal. The fluoride-triggered desilylation showed a high reaction rate and high affinity to F− over nine other interfering anions. ES-1 provided a novel fluorescence assay based on excimer–monomer switch of N-aryl-1,8-naphthalimide to quantitatively measure F− with a detection limit of 0.133 ppm.
TL;DR: Thermodynamic and kinetic comparisons of Zn(2+) binding properties of ethylenediamine-based hexadentate ligands with pyridines and (iso)quinolines are comprehensively discussed.
Abstract: Zn2+-induced fluorescence enhancement of the TPEN (N,N,N′,N′-tetrakis(2-pyridylmethyl)ethylenediamine)-based ligand, N,N-bis(1-isoquinolylmethyl)-N′,N′-bis(pyridylmethyl)ethylenediamine (N,N-1-isoBQBPEN, 1b), has been investigated. Upon Zn2+ binding, 1b shows a fluorescence increase (ϕZn = 0.028) at 353 and 475 nm. The fluorescence enhancement at longer wavelengths is due to intramolecular excimer formation of two isoquinolines and is specific for Zn2+; Cd2+ induces very small fluorescence at 475 nm (ICd/IZn = 10%). The excimer formation of the [Zn(1b)]2+ complex in the excited state is supported by the time-dependent DFT calculation. Neither long-wavelength fluorescence nor excimer formation is observed in the Zn2+ complex of N,N′-1-isoBQBPEN (2b). The quinoline analog N,N-BQBPEN (1a) exhibits similar but significantly smaller excimer formation. Thermodynamic and kinetic comparisons of Zn2+ binding properties of ethylenediamine-based hexadentate ligands with pyridines and (iso)quinolines are comprehensively discussed.
TL;DR: In this article, four CH2OH groups were added to an anthracene bridged Zn-DPA complex to produce a new highly selective and controllable excimer-based fluorescent sensor for pyrophosphate in water.
Abstract: Introducing four –CH2OH groups to an anthracene bridged Zn–DPA complex was found to result in a new highly selective and controllable excimer-based fluorescent sensor for pyrophosphate in water.
TL;DR: Time-resolved fluorescence measurements on compound 6 with F(-) and AcO(-) confirmed that the 472 nm emission band mainly came from static excimers for the former, but was partly from a dynamic excimer for the latter because it contained a growth component in the fluorescence decay traces.
Abstract: 25,27-Bis{1′-N-(1-pyrenyl)-aminocarbonylmethyl-1H-[1′,2′,3′]tri-azolyl-4′-methoxy}-26,28-dihydroxycalix[4]arene, 4, is synthesized as a fluorescent chemosensor for the selective detection of both anions and ion pairs in MeCN. Sensor 4 uses bis-triazoles as ligands to bind a metal ion, bis-amides and bis-triazoles as the sites to recognize anions, and pyrenes as fluorophores. Among eight anions screened, chemosensor 4 showed a marked fluorescence change toward F−, H2PO4− and AcO−, but 4 responded to each anion in a distinct way. In the presence of F− at low concentrations, the dynamic excimer emission of compound 4 at λmax 482 nm was quenched, but an emission at λmax 472 nm appeared at large doses of F−. A control compound 6 showed very similar red shifts in the UV-vis and excitation spectra as 4 did, and its 472 nm emission band grew as the fluoride doses increased. Thus, the growth of the 472 nm emission of 4 and 6 in the presence of excess F− may be because strong H-bonding interactions of amido protons with F− favoured the formation of pyrene dimers in the ground state with charge transfer characteristics. The addition of H2PO4−, unlike F−, to a solution of 4 showed an enhanced monomer emission but a decreased excimer emission (λmax 482 nm). Adding AcO− to 4 produced a systematic change from a dynamic excimer (λmax 482 nm) to λmax 472 nm but with very little change in the UV-vis spectrum. Time-resolved fluorescence measurements on compound 6 with F− and AcO− confirmed that the 472 nm emission band mainly came from static excimers for the former, but was partly from a dynamic excimer for the latter because it contained a growth component in the fluorescence decay traces. Without pre-treatment with an anion, chemosensor 4 showed recognition of only metal ions Cu2+, Hg2+ and Cr3+, but it became sensitive to Ag+ when it was pretreated with fluoride.
TL;DR: In this paper, a method of rapid conversion of a hydrophobic to hydrophilic state of an Si (0 0 1) surface irradiated with a relatively low number of pulses of an excimer laser was reported.
Abstract: We report on a method of rapid conversion of a hydrophobic to hydrophilic state of an Si (0 0 1) surface irradiated with a relatively low number of pulses of an excimer laser. Hydrophilic Si (0 0 1), characterized by the surface contact angle (CA) of near 15 ◦ ,i s fabricated following irradiation with either KrF or ArF excimer lasers of hydrophobic samples (CA ∼ 75 ◦ ) immersed in a 0.01% H2O2/H2O solution. The chemical and structural analysis carried with x-ray photoelectron spectroscopy and atomic force microscopy measurements confirmed the formation of OH-terminated Si (0 0 1) surface with no detectable change in the surface morphology of the laser-irradiated material. To investigate the efficiency of this laser-induced hydrophilization process, we demonstrate a selective area immobilization of biotin-conjugated fluorescein-stained nanospheres outside of the laser-irradiated area. The results demonstrate the potential of the method for the fabrication of biosensing architectures and advancements of the Si-based microfluidic device technology.
TL;DR: A new probe architecture is introduced to enable the switching on of pyrene excimer emission upon proteolytic scission and time-resolved measurements allowed the detection of matrix metalloprotease 7 in human blood serum.
Abstract: Peptide-based probes that fluoresce upon proteolytic cleavage are invaluable tools for monitoring protease activity. The read-out of protease activity through pyrene excimer signaling would be a valuable asset because the large Stokes shift and the long lifetime of the excimer emission facilitate measurements in autofluorescent media such as blood serum. However, proteolytic cleavage abolishes rather than installs the proximity relationships required for excimer signaling. Herein, we introduce a new probe architecture to enable the switching on of pyrene excimer emission upon proteolytic scission. The method relies on hairpin-structured peptide nucleic acid (PNA)/peptide hybrids with pyrene units and anthraquinone-based quencher residues positioned in a zipper-like arrangement within the PNA stem. The excimer hairpin peptide beacons afforded up to a 50-fold enhancement of the pyrene excimer emission. Time-resolved measurements allowed the detection of matrix metalloprotease 7 in human blood serum.
TL;DR: In this article, an aggregationenhanced excimer emission (AEEE) fluorophore was successfully synthesized by introducing chalcone into pyrene and a probe with good water solubility based on pyrenylchalcone was designed for polyanion detection in aqueous media.
Abstract: An aggregation-enhanced excimer emission (AEEE) fluorophore was successfully synthesized by introducing chalcone into pyrene. Compared with the traditional AIE structure (tetra-phenylethene derivatives), pyrenylchalcone was more available under mild conditions. It exhibited weak emission when molecularly dissolved but strong excimer emission when aggregated. Then we designed a probe with good water solubility based on pyrenylchalcone for polyanion detection in aqueous media. An orange emission could be observed upon simple addition of polyacrylic acid sodium salt. Better than the other “blue-to-green” pyrene probes, this “turn-on” AEEE probe was more likely visible to eyes. Moreover, unlike the double bond in tetra-phenylethene, the unsaturated double bond in chalcone could be easily opened by thiols. It could lead to another different “turn-on” change in fluorescence. Adding biothiol and adding polyanion were two different methods to reduce the intra-molecular rotations and cause different emissions, thus we built a 2-to-4 molecular decoder in aqueous media which could be observed by naked eyes.
TL;DR: A simple pyrene based receptor has been synthesised and shown to exist in the dimeric form in solution exhibiting an excimer band in the emission spectrum and working on the solid support; thus attesting the potential of the sensor for practical application in contact mode.
TL;DR: A series of 2,2-disubstituted benzothiazoline-BMes2 (Mes = mesityl) compounds containing a B═N bond have been prepared and fully characterized.
TL;DR: In this article, the structure of the (dibenzoylmethanato)boron difluoride molecule (DBMBF2) and its complexes with a series of aromatic hydrocarbons (benzene; toluene; o-, m-, and p-xylenes, naphthalene; anthracene; and pyrene) in the ground and the first singlet excited states have been calculated.
Abstract: Structures of the (dibenzoylmethanato)boron difluoride molecule (DBMBF2) and its complexes with a series of aromatic hydrocarbons (benzene; toluene; o-, m-, and p-xylenes, naphthalene; anthracene; and pyrene) in the ground and the first singlet excited states have been calculated. The calculations have been performed by the density functional theory (DFT) and time-dependent density functional theory (TDDFT) for the ground and excited states, respectively, with the empirical dispersion correction. It has been shown that the complexes in the ground and excited states have similar stacking structures and are characterized by short contacts between the F atom of DBMBF2 and H atoms of the hydrocarbon molecule, which decrease on transition from the ground to the excited state. The calculated binding energies in the complexes in the excited state are two to three times higher than those in the ground state. The charge transfer in the ground state of the complexes is insignificant and directed from DBMBF2 to the ligand, while in the excited state it is 0.6–0.8 e and directed from the ligand to DBMBF2.
TL;DR: Geometry relaxation effects on the formation of benzene excimer were investigated by means of ab initio calculation at SOS-CIS(D0)/aug-cc-pVDZ level as mentioned in this paper.
Abstract: Geometry relaxation effects on the formation of benzene excimer were investigated by means of ab initio calculation at SOS-CIS(D0)/aug-cc-pVDZ level. In the case of T-shaped dimer configuration, intermolecular interactions in the excited states are found to be nearly the same as those in the ground state and structural deformations are limited within a single molecule; the geometry relaxation effects are then negligible and singlet-triplet energy gap remains constant. As for face-to-face eclipsed dimer, on the other hand, both molecules undergo structural change. As a result, intermolecular interactions in the excited states are significantly different than those in the ground state. Although the intermolecular distances obtained from potential energy curve calculation with frozen molecular structures are in qualitative agreement, the excitedstate binding energies are notably overestimated with respect to those at optimized structures. In particular, the effects are calculated to be larger in T1 state and hence singlet-triplet energy gap, which reduces markedly in this configuration, is underestimated without relaxation.
TL;DR: In this paper, the authors reported the formation and control of excimer of 7-Hydroxy-N-Octadecyl Coumarin-3-Carboxamide (7HNO3C) assembled onto Langmuir-Blodgett (LB) films.
TL;DR: In this article, the authors demonstrated the selectivity and fluorescence sensitivity of a well-recognized antiexcitotoxic and anticonvulsant drug, kynurenic acid (KA), toward Cd II ion using 1 H NMR spectroscopy in combination with computational calculations.
TL;DR: In this article, the effect of strong interaction between π-orbitals of closely spaced benzene rings of the molecule resulted in formation of an excited state of lower energy that was new in principle.
Abstract: The significant bathochromic shift of luminescence and long-wavelength absorption bands of [2.2]paracyclophane compared with the corresponding bands for molecules containing non-conjugated benzene chromophores was examined. The effect was due to strong interaction between π-orbitals of closely spaced benzene rings of the molecule that resulted in formation of an excited state of lower energy that was new in principle. It was concluded that the fluorescent state of the macrocycle and excimers formed by alkylbenzenes were of the same nature. The lowest electronic excited state of [2.2]paracyclophane appeared not only in emission but also in absorption. This explained the lack of an anomalous Stokes shift for it. The stronger shift of the macrocycle fluorescence band compared with the excimer band of alkylbenzenes was due to the fact that the highest occupied π-orbital of [2.2]paracyclophane was perturbed and located higher on the energy scale than for the chromophores of alkylbenzenes and polystyrene.