Excited state behaviour of pentahelicene dinitriles

Gorner H, Stammel C, Mattay J. Excited state behaviour of pentahelicene dinitriles. Journal of Photochemistry and Photobiology A Chemistry. 1999;120(3):171-179.The excited singlet and triplet states 2, 13-dicyano[5]helicene (1) and two para-dicyno[5]helicenes containing one and two methyl groups (2 and 3, respectively) were studied in solvents of different polarity as a function of temperature. Fluorescence quenching by electron donors such as triethyl amine indicated photoinduced electron transfer. In the absence of additives triplet states were observed by flash photolysis. The triplet lifetime at room temperature was rather short (