Anthralin-derived transients--I. The triplet state and the products of its reaction with oxygen in benzene

Direct laser excitation in benzene of 1,8-dihydroxy-9-anthrone (anthralin) does not lead to transient species with lifetimes in the nanosecond time regime or longer. The triplet state has been produced in benzene by pulse radiolysis and characterised in terms of its absorption spectrum (lambda max 560 nm), natural lifetime (11 microseconds), self-quenching properties (kmicrosecond = 2.6 x 10(7) l mol-1 s-1) and triplet energy (234 kJ mol-1). There is no tendency in the non-polar medium for production of either the triplet or ground state in a tautomeric form. The observed triplet state reacts with oxygen with a typical rate constant, 2.2 x 10(9) l mol-1 s-1. The products of this reaction are singlet oxygen (approximately 64%) and the anthralin radical (approximately 14%).