The photophysical and photochemical features of trans isomers of 1-styrylpyrene (StPy) and 3-styrylchrysene (StCh) have been studied in benzene and acetonitrile solution at room temperature, and in 2-methyltetrahydrofuran (MTHF) at low temperatures. The major deactivation process of the excited trans si ng let state ((1)trans*) is fluorescence, (fluorescence quantum yield, phi(F) = 0.7-0.9), whereas singlet --> triplet (S-1 --> T-1) intersystem crossing is inefficient (as is trans --> cis photoisomerization of StPy). Quenching of the (1)trans* state by diethylaniline (DEA) leads to an exciplex fluorescence in benzene. Fluorescence quenching by 4-bromodimethylaniline (via the external heavy-atom effect) enhances the formation of the trans triplet configuration ((3)trans*). In acetonitrile, the radical anion (trans(.-)) of the two 1,2-diarylethenes was observed by optical and conductometric detection in the presence of DEA. Photoionization with a low quantum yield (phi(PI) = 0.007-0.015) was observed in neat acetonitrile. The properties of the radical cation (trans(.+)) were studied after photoinduced electron transfer from (1)trans* to 1,4-dicyanobenzene (DCNB). The effect of temperature on the yield and decay kinetics of (3)trans* was analysed for StCh in MTHF and a mechanism is proposed for the trans --> cis photoisomerization via an upper excited triplet state.
Triplet and radical ion properties of trans-1-styrylpyrene and trans-3-styrylchrysene isomers
ELISEI, Fausto;LATTERINI, Loredana;
1995
Abstract
The photophysical and photochemical features of trans isomers of 1-styrylpyrene (StPy) and 3-styrylchrysene (StCh) have been studied in benzene and acetonitrile solution at room temperature, and in 2-methyltetrahydrofuran (MTHF) at low temperatures. The major deactivation process of the excited trans si ng let state ((1)trans*) is fluorescence, (fluorescence quantum yield, phi(F) = 0.7-0.9), whereas singlet --> triplet (S-1 --> T-1) intersystem crossing is inefficient (as is trans --> cis photoisomerization of StPy). Quenching of the (1)trans* state by diethylaniline (DEA) leads to an exciplex fluorescence in benzene. Fluorescence quenching by 4-bromodimethylaniline (via the external heavy-atom effect) enhances the formation of the trans triplet configuration ((3)trans*). In acetonitrile, the radical anion (trans(.-)) of the two 1,2-diarylethenes was observed by optical and conductometric detection in the presence of DEA. Photoionization with a low quantum yield (phi(PI) = 0.007-0.015) was observed in neat acetonitrile. The properties of the radical cation (trans(.+)) were studied after photoinduced electron transfer from (1)trans* to 1,4-dicyanobenzene (DCNB). The effect of temperature on the yield and decay kinetics of (3)trans* was analysed for StCh in MTHF and a mechanism is proposed for the trans --> cis photoisomerization via an upper excited triplet state.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
