Excited-state dynamics in an α-perylene single crystal: two-photon- and consecutive two-quantum-induced singlet fission.
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.
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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: Five covalently bound PMI dimers with varying degrees of electronic interaction were studied to probe the relative chromophore orientations that lead to excimer energy trap states and provide structural insights for minimizing excimer trap states in organic devices based on PMI derivatives.
Abstract: Robust perylene-3,4-dicarboximide (PMI) π-aggregates provide important light-harvesting and electron–hole pair generation advantages in organic photovoltaics and related applications, but relatively few studies have focused on the electronic interactions between PMI chromophores. In contrast, structure–function relationships based on π–π stacking in the related perylene-3,4:9,10-bis(dicarboximides) (PDIs) have been widely investigated. The performance of both PMI and PDI derivatives in organic devices may be limited by the formation of low-energy excimer trap states in morphologies where interchromophore coupling is strong. Here, five covalently bound PMI dimers with varying degrees of electronic interaction were studied to probe the relative chromophore orientations that lead to excimer energy trap states. Femtosecond near-infrared transient absorption spectroscopy was used to observe the growth of a low-energy transition at ∼1450–1520 nm characteristic of the excimer state in these covalent dimers. The ...
115 citations
TL;DR: Two dimers of perylene bound either directly or through a xylyl spacer to a xanthene backbone were synthesized to probe the effects of interchromophore electronic coupling on excimer formation and SB-CS using ultrafast transient absorption spectroscopy.
Abstract: The use of multiple chromophores as photosensitizers for catalysts involved in energy-demanding redox reactions is often complicated by electronic interactions between the chromophores. These interchromophore interactions can lead to processes, such as excimer formation and symmetry-breaking charge separation (SB-CS), that compete with efficient electron transfer to or from the catalyst. Here, two dimers of perylene bound either directly or through a xylyl spacer to a xanthene backbone were synthesized to probe the effects of interchromophore electronic coupling on excimer formation and SB-CS using ultrafast transient absorption spectroscopy. Two time constants for excimer formation in the 1–25 ps range were observed in each dimer due to the presence of rotational isomers having different degrees of interchromophore coupling. In highly polar acetonitrile, SB-CS competes with excimer formation in the more weakly coupled isomers followed by charge recombination with τCR = 72–85 ps to yield the excimer. The ...
90 citations
TL;DR: The results show that significantly different crystal morphologies of the same chromophore can both result in high-efficiency SF provided that the energetics are favorable.
Abstract: Two terrylene chromophores, 2,5,10,13-tetra(tert-butyl)terrylene (1) and 2,5-di(tert-butyl)terrylene (2), were synthesized and studied to determine their singlet exciton fission (SF) efficiencies. Compound 1 crystallizes in one-dimensional stacks, whereas 2 packs in a slip-stacked, herringbone pattern of dimers motif. Strongly quenched fluorescence and rapid singlet exciton decay dynamics are observed in vapor-deposited thin films of 1 and 2. Phosphorescence measurements on thin films of 1 and 2 show that SF is only 70 meV endoergic for these chromophores. Femtosecond transient absorption experiments using low laser fluences on these films reveal rapid triplet exciton formation for both 1 (τ = 120 ± 10 ps) and 2 (τ = 320 ± 20 ps) that depends strongly on film crystallinity. The transient absorption data are consistent with formation of an excimer state prior to SF. Triplet exciton yield measurements indicate nearly quantitative SF in thin films of both chromophores in highly crystalline solvent-vapor-anne...
89 citations
TL;DR: An in-depth discussion of the properties of perylene is presented and the synthesis and properties of oligorylenes functionalized with dicarboxyimide bonds are discussed.
Abstract: An in-depth discussion of the properties of perylene is presented. Tuning the properties of perylene by introducing nitrogens is also explored. Finally, we do not discuss the synthesis and properties of oligorylenes functionalized with dicarboxyimide bonds.
76 citations
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TL;DR: Self-organization of liquid crystalline and crystalline-conjugated materials has been used to create, directly from solution, thin films with structures optimized for use in photodiodes, demonstrating that complex structures can be engineered from novel materials by means of simple solution-processing steps and may enable inexpensive, high-performance, thin-film photovoltaic technology.
Abstract: Self-organization of liquid crystalline and crystalline-conjugated materials has been used to create, directly from solution, thin films with structures optimized for use in photodiodes. The discotic liquid crystal hexa-peri-hexabenzocoronene was used in combination with a perylene dye to produce thin films with vertically segregated perylene and hexabenzocoronene, with large interfacial surface area. When incorporated into diode structures, these films show photovoltaic response with external quantum efficiencies of more than 34 percent near 490 nanometers. These efficiencies result from efficient photoinduced charge transfer between the hexabenzocoronene and perylene, as well as from effective transport of charges through vertically segregated perylene and hexabenzocoronene pi systems. This development demonstrates that complex structures can be engineered from novel materials by means of simple solution-processing steps and may enable inexpensive, high-performance, thin-film photovoltaic technology.
2,234 citations
849 citations
TL;DR: Physical vapor growth in horizontal and vertical systems has been used to grow crystals of α-hexathiophene (α-6T), α-octithiophene, α-4T, pentacene, anthracene and copper phthalocyanine.
604 citations
TL;DR: In this article, a new crystalline form of perylene has been found and its crystal structure has been determined by the two-dimensional X-ray diffraction method, which is explained as a stabilization of the lowest excited singlet state by a charge-transfer resonance interaction between the molecules in a pair.
Abstract: A new crystalline form of perylene has been found and its crystal structure has been determined by the two-dimensional X-ray diffraction method. The new form is monomeric, while the previously known form has a dimeric structure. The electronic absorption and fluorescence spectra of both forms have been measured ; on the basis of these data, an assignment is proposed for the observed transitions. Although the fluorescence spectrum of the monomer form shows a small shift, that of the dimer form shows a larger shift than would be expected from the absorption spectrum. This is explained as a stabilization of the lowest excited singlet state by a charge-transfer resonance interaction between the molecules in a pair. Because this stabilization increases as the distance between two molecules decreases, it is suggested that the molecules in a pair approach each other after excitation. At the liquid helium temperature the motion of molecules in the crystal will be frozen out, the larger stabilization of the excite...
305 citations
TL;DR: In this paper, the triplet-triplet absorption spectra of a variety of organic molecules have been observed in fluid solutions at normal temperatures and the effect of dissolved gases, particularly oxygen, on these lifetimes is described.
Abstract: Absorption spectra of the triplet states of a variety of organic molecules have been observed in fluid solutions at normal temperatures. Triplet-triplet spectra are given for thirty-two molecules and, for ten of these, absolute extinction coefficients and oscillator strengths have been measured. In most cases several distinct electronic transitions have been found and the energy levels and oscillator strengths of these transitions are compared with the results of molecular orbital calculations for the first five linear polyacenes. Triplet-state lifetimes have been measured for naphthalene and anthracene in a wide range of solvents and the effect of dissolved gases, particularly oxygen, on these lifetimes is described.
208 citations