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Photoinduced Intramolecular Charge Transfer and S 2 Fluorescence in Thiophene‐π‐Conjugated Donor–Acceptor Systems: Experimental and TDDFT Studies
Author(s) -
Zhao GuangJiu,
Chen RuiKui,
Sun MengTao,
Liu JianYong,
Li GuangYue,
Gao YunLing,
Han KeLi,
Yang XiChuan,
Sun Licheng
Publication year - 2008
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200701868
Subject(s) - solvatochromism , intramolecular force , time dependent density functional theory , photochemistry , thiophene , chemistry , stokes shift , acceptor , fluorescence , conjugated system , emission spectrum , density functional theory , computational chemistry , spectral line , solvent , polymer , organic chemistry , physics , quantum mechanics , astronomy , condensed matter physics
Experimental and theoretical methods were used to study newly synthesized thiophene‐π‐conjugated donor–acceptor compounds, which were found to exhibit efficient intramolecular charge‐transfer emission in polar solvents with relatively large Stokes shifts and strong solvatochromism. To gain insight into the solvatochromic behavior of these compounds, the dependence of the spectra on solvent polarity was studied on the basis of Lippert–Mataga models. We found that intramolecular charge transfer in these donor–acceptor systems is significantly dependent on the electron‐withdrawing substituents at the thienyl 2‐position. The dependence of the absorption and emission spectra of these compounds in methanol on the concentration of trifluoroacetic acid was used to confirm intramolecular charge‐transfer emission. Moreover, the calculated absorption and emission energies, which are in accordance with the experimental values, suggested that fluorescence can be emitted from different geometric conformations. In addition, a novel S 2 fluorescence phenomenon for some of these compounds was also be observed. The fluorescence excitation spectra were used to confirm the S 2 fluorescence. We demonstrate that S 2 fluorescence can be explained by the calculated energy gap between the S 2 and S 1 states of these molecules. Furthermore, nonlinear optical behavior of the thiophene‐π‐conjugated compound with diethylcyanomethylphosphonate substituents was predicted in theory.