The photophysics and photochemistry of several sulphonated derivatives of 9 ,1 0 -anthraquinone have been investigated using steady-state and time-resolved absorption, emission, and Raman spectroscopy. These molecules are of interest because of their potential application as photosensitising agents in oxygenated aqueous solution, and it is principally under these conditions that they have been studied. Time-resolved absorption spectroscopy has led to the proposal of a complicated mechanism for the aqueous solution photochemistry of the so-called 'strong* sensitisers, and the triplet state has been observed to decay with the production of three different transient species including two different complexes with water. These observations have allowed correlation to be made between species observed on the nanosecond to microsecond timescale following nanosecond pulsed laser excitation and the hydroxylated derivatives obtained as permanent products on steady-state irradiation. These reactions are important since they constitute undesirable side reactions in any potential catalytic photochemical system. The 'weak1 sensitisers have also been studied, but it has been found that the major route of triplet decay is return to the ground state of the molecule. The semiquinone radical anions and neutral radicals have also been produced in aqueous solution by electron transfer, and their spectra and kinetics characterised.