Photophysics and photochemistry of sulphonated derivatives of 9,10-anthraquinone. ‘Strong’versus‘weak’ sensitisers

Abstract

The photophysics and photochemistry of a series of sulphonated derivatives of 9,10-anthraquinone have been investigated using steady-state and transient optical absorption and emission spectroscopy. The identity and kinetics of the transient species observed following nanosecond photolysis of the ‘strong’ sensitisers are similar to those previously established for anthraquinone-2,6-disulphonate. The ‘weak’ sensitisers display similar characteristics on photolysis, although these have been found to be distinct from those of the ‘strong’ sensitisers. Only one transient species, assigned to the triplet state has been observed following photolysis of the ‘weak’ sensitisers in aqueous solution. Distinct differences have also been observed in the emission spectroscopy of the ‘strong’ and ‘weak’ sensitisers. It is proposed that the differences between the two sets of compounds may be explained by the nature of their lowest-energy triplet states, these being nπ* for the ‘strong’ sensitisers and ππ* for the ‘weak’ sensitisers.