In the present work, we investigated the photophysical and photosensitive properties and further explored the substituent effects on these properties of a series of anthraquinones by means of theoretical calculations. It is revealed that comparing with the parent 9,10-anthraquinone (AQ), the substitutents red-shifted the absorption spectra and lowered the E T1 of anthraquinones considerably. Moreover, the present results also provide some deeper insights into the photosensitization mechanisms of anthraquinones, that is, although anthraquinones can photo-generate 1 O 2 through direct energy transfer in both non-polar and polar solvents, they give birth to O2- through electron transfer only in polar solvents, and it is the anthraquinones anions (generated from autoionization) that are responsible for the O2--generation.