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7662852 
Journal Article 
ROLE OF CHARGE-TRANSFER INTERACTIONS IN PHOTOREACTIONS .6. PHOTOINDUCED ELECTRON-TRANSFER AND TRANS-]CIS ISOMERIZATION FOR STYRYLPHENANTHRENE AMINE SYSTEMS IN ACETONITRILE 
Aloisi, GG; Elisei, F; Gorner, H; , 
1991 
1 
Journal of Physical Chemistry
ISSN: 0022-3654 
AMER CHEMICAL SOC 
WASHINGTON 
4225-4231 
WOS:A1991FP24100012 
The decay pathways of the lowest excited singlet state (S1) of trans-n-styrylphenanthrenes (n-StPh, with the location on phenanthrene n = 1,2,3,4, and 9) were studied in acetonitrile at room temperature. Fluorescence lifetimes (tau-F), quantum yields of fluorescence (PHI-F) and intersystem crossing (PHI-T(max)), some properties of the lowest triplet state (T1), and the quantum yield of trans --> cis photoisomerization (PHI-C) were determined for the five isomers. Evidence is obtained for three different routes in the trans --> cis photoisomerization: (i) a trans --> perp rotation via T1 for 4-StPh, (ii) involvement of both T1 (congruent-to 20%) and mainly S1 for 9-StPh, and (iii) rotation via an upper triplet state for the others. The formation and decay of the five respective StPh radical cations in the absence of additives were observed by laser flash photolysis. On 353-nm excitation the yield is low (< 0.1) but enhanced by fluorescence quenching with 1,4-dicyanobenzene; ionization of StPh's is supported by excitation at 248 nm in ethanol/water, where the solvated electron was also detected. The formation and decay of the five StPh radical anions are evidenced from optical and transient conductivity results in the presence of amines. They significantly enhance the initial amplitude of the transient conductivity signal and correspondingly quench PHI-F, tau-F, and PHI-C (the latter only to a lesser extent in some cases). The bimolecular interaction between 1trans* and 4-bromodimethylaniline yields a larger triplet formation and only in some cases an increase of photoisomerization efficiency, with respect to those of the free olefin. Reactions with diethylaniline and tributylamine generate ion pairs. It is concluded that ion-pair recombination is an inefficient pathway to the triplet formation for trans-StPh's.