Time-resolved fluorescence of α-(9-anthryl)-ω-(1-naphthyl)-oligosilanes: intramolecular electronic energy and charge transfer through π–π and σ–π interactions

Karatsu, Takashi; Terasawa, Masato; Yagai, Shiki; Kitamura, Akihiro; Nakamura, Takashi; Nishimura, Yukio; Yamazaki, Iwao

doi:10.1016/j.jorganchem.2003.12.038

Cited by 12 publications

(4 citation statements)

References 18 publications

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“…This phenomenon can be explained by the shielding effect of the five-membered ring moiety of C 60 or by the reduction in the ring current of the ZnP ring with the attachment of an electron-withdrawing C 60 . , The signals of the three protons of the pyrrolidine moiety of ZnP−[Si 2 ]−C 60 (δ H 3.54, 4.27, and 4.39 ppm) appeared in a higher magnetic field region than those of the fullerene reference [Si 2 ]−C 60 (δ H 3.83, 4.51, and 4.72 ppm) and are attributed to the shielding effect of the porphyrin ring. The formation of folded conformers is also in agreement with the observation of the greatest shift for ZnP−[Si 2 ]−C 60 , in which the ZnP moiety can approach the C 60 moiety most easily (“sila-Hirayama rule”) . Folded conformers are supposed to be in fast equilibrium with extended conformers (an example for n = 5 in Figure B), and averaged signals could not be separated even at low temperatures.…”

Section: Resultssupporting

confidence: 82%

Oligosilane Chain-Length Dependence of Electron Transfer of Zinc Porphyrin−Oligosilane−Fullerene Molecules

et al. 2007

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A new series of zinc porphyrin-fullerenes bridged by flexible oligosilane chains ZnP-[Sin]-C60 (n = 1-5) was synthesized, and the photophysical properties of these molecules were investigated using steady-state and time-resolved spectroscopic methods. The spectral observations can be well explained by assuming the coexistence of extended conformers and folded conformers, that is, the observed emissions are from the extended conformers while the folded conformers form very short lifetime nonfluorescent excited-state charge-transfer (CT) complexes. Time-resolved transient absorption spectra suggest the generation of intramolecular radical-ion pairs that have sub-microsecond lifetimes. With the number of silicon atoms of the bridged oligosilane, the lifetimes of the radical-ion pairs do not vary regularly, indicating that intramolecular collision of the radical-cation moiety with the radical-anion moiety controls the charge-recombination rate. The attenuation factor of the electron transfer of the silicon chain was evaluated by the bridge-length dependence of charge-separation rate to be 0.16 A-1 on the basis of the oligosilane chain-length dependence of fluorescence lifetimes. This is the first evaluation of the attenuation factor for the one-dimensional Si-Si chain to the best of our knowledge.

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Section: Resultssupporting

confidence: 82%

Oligosilane Chain-Length Dependence of Electron Transfer of Zinc Porphyrin−Oligosilane−Fullerene Molecules

et al. 2007

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“…The incorporation of oligosilyl groups into π-conjugated frameworks allows their photophysical and electrochemical properties to be tuned via hyperconjugation . Previously, we found that hydrosilanes can be easily coupled with organic halides containing various functional groups in the presence of a transition metal catalyst and a base .…”

Section: Introductionmentioning

confidence: 99%

Structures and Optical Properties of Tris(trimethylsilyl)silylated Oligothiophene Derivatives

et al. 2014

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The structures and optical properties of tris(trimethylsilyl)silylated oligothiophenes were examined by spectroscopies, theoretical calculations, and single-crystal X-ray measurements. Bathochromic shift from the original oligothiophenes was observed in the tris(trimethylsilyl)silylated ones, confirming the σ-π conjugation between Si-Si σ bonds and π-orbital. 5,5'-Bis(tris(trimethylsilyl)silyl)-2,2'-bithiophene (Si-T2) showed the highest fluorescence quantum yield (ΦF) both in solution (0.67, excited at 350 nm) and the solid state (0.74, excited at 371 nm). The introduction of tris(trimethylsilyl)silyl groups led to the small nonradiative rate constant of Si-T2, resulting in the high ΦF in the solution state. Si-T2 also exhibited effective σ-π conjugation and poor molecular interaction, which reflected its high ΦF in the solid state. On the contrary, lower ΦF (0.13, excited at 331 nm) in the solid state was observed in the longest oligothiophene examined, 5,5‴-bis(1,1,1,3,3,3-hexamethyl-2-(trimethylsilyl)trisilan-2-yl)-2,2':5',2″:5″,2‴-quaterthiophene (Si-T4). Single-crystal X-ray measurement clarified that this compound adopted a zigzag packing structure and a rare syn-anti-syn conformation, which led to the poor σ-π conjugation and the decrease of π-orbital overlap in the solid state.

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“…FL is an important technique to characterize the size distribution of fused aromatic fragments but also to provide the information on aggregation between aromatic fluorophors. − Although 2–3 rings fused aromatic fragments, such as naphthalene, anthracene, and phenanthrene rings, are prevalent in PA and its subfractions according to their absorbance spectra, the emission spectra shown in Figure display exclusively a nonstructural broad band without any fluorescent of monomers (the emission of locally excited state), suggesting that there should be complex photophysical processes such as excimer/exciplex formations, intramolecular charger-transfer, and electronic energy transfer . However, compared with the emission spectra of polymer labeled by aryl group and diarylalkane, in which more or less emission of single aryl can be observed beside the emission of excimer, there are no any emission of single fluorophor in the fluorescence spectra of PA and its subfractions.…”

Section: Resultsmentioning

confidence: 99%

Structural Characterization and Aggregation of the Subfractions of Preasphaltene from Direct Coal Liquefaction

et al. 2014

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Preasphaltene (PA) defined as tetrahydrofuran (THF) soluble and toluene insoluble is an important intermediate product of direct coal liquefaction (DCL). Investigating the structure of PA not only can improve the DCL technology but also can help us understand the structure of coal. In this paper, two types of PAs from the DCL residue of 6 t/d Shenhua process developing unit (PDU) and the products of a batch hydroliquefaction in an autoclave were first separated into different subfractions by the column chromatography. Then, the obtained subfractions were characterized by Fourier transform infrared spectroscopy (FTIR), ultraviolet−visible spectroscopy (UV) and fluorescence spectroscopy (FL), matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) and gel permeation chromatography (GPC), respectively. The results indicate that the PA from DCL mainly exists in the form of aggregates. Two different PAs show similar distribution of subfractions, but the PA(B) obtained by the batch liquefaction displays larger molecular weight than the PA(A) from Shenhua PDU technology. A molecule of PA contains two or more aromatic nuclei (fluorophors). Subfractions I−III consist of smaller fused aromatic nucleus than the other subfractions. In general, their intermolecular aggregations increase from subfraction I to VII, and the aggregation of PA(A) subfractions is stronger than that of corresponding PA(B) subfractions.

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Time-resolved fluorescence of α-(9-anthryl)-ω-(1-naphthyl)-oligosilanes: intramolecular electronic energy and charge transfer through π–π and σ–π interactions

Cited by 12 publications

References 18 publications

Oligosilane Chain-Length Dependence of Electron Transfer of Zinc Porphyrin−Oligosilane−Fullerene Molecules

Oligosilane Chain-Length Dependence of Electron Transfer of Zinc Porphyrin−Oligosilane−Fullerene Molecules

Structures and Optical Properties of Tris(trimethylsilyl)silylated Oligothiophene Derivatives

Structural Characterization and Aggregation of the Subfractions of Preasphaltene from Direct Coal Liquefaction

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