Abstract: Fluorescence emission of 6-cyanotricyclo [5.5. O. Oz~ s] dodeca-3, 6, 8, lO, l2- pentaene (1) is observed only from the second excited singlet states S2 (@ f= 3 X lo-', 7f= 82 ps) but not from S, in violation of Kasha's rule. Nonfused cyanoheptafulvenes are nonfluorescent due to a “free rotor effect” of the exocyclic double bond. The previously reported dependence of the photochemical valence isomerization of 1 on the excitation ...