Reversible photochemistry and photocyclization of 10H,10′H-bianthrylidene

Abstract

The photochemistry of 10,H,10′H-bianthrylidene was extensively studied over a wide temperature range. Two photoisomers, C and E, are formed, both reverting thermally to the parent modification A. The C isomer is a cyclization product of the 4a,4b-dihydrophenanthrene type, whereas the E isomer results from cis–trans-isomerization about the central double bond together with additional torsions about the four single bonds of the 9,9′-ethylene system. The A, E, and C modifications are oxidized by atomic iodine. The dependence of the quantum yield of fluorescence on temperature indicates that intersystem crossing is an activated process above a certain critical temperature (ca.–130°) and non-activated at lower temperatures. The C modification is formed from the excited singlet and the E isomer from the triplet state.