Electron transfer from ground-state triethylamine to the lowest excited triplet states of chloroanthraquinones (the 1-chloro, 2-chloro, 1,5-dichloro and 1,8-dichloro compounds) in ethanol and toluene at room temperature

Abstract

Upon picosecond and nanosecond laser photolysis of the title compounds (XAQ) at room temperature in ethanol and toluene containing triethylamine (TEA), the lowest excited triplet states of XAQ react with ground-state TEA, forming the exciplexes [3(XAQ–TEA)*] which change to the contact ion pairs [3(XAQ˙––TEA˙+)] of the XAQ radical anions (XAQ˙–) with the TEA radical cation (TEA˙+); this is followed by proton transfer, generating XAQ semiquinone radicals and the TEA radical. Since not only the decay constants of 3(XAQ–TEA)* but also the quantum yields of photoreduction are affected by a change in the TEA concentration, the existence of a rapid interconversion between 3(XAQ–TEA)* and the triplexes [3(XAQ–TEA2)*] of 3(XAQ–TEA)* with TEA is proposed. For 1,8-dichloroanthraquinone (1,8-DCAQ) in toluene–TEA there also exists a rapid interconversion between 3(XAQ˙––TEA˙+) and a complex [3(XAQ˙––TEA˙+2)] formed between the 1,8-DCAQ radical anion and the TEA dimer radical cation.