Density functional theory (DFT) and time-dependent DFT (TD-DFT) provide new insights into the photodegradation pathways of the cytotoxic complex cis,trans,cis-[Pt(N-3)(2)(OH)(2)(NH3)(2)] allowing assignment of (LMCT)-L-1 transitions in the visible region of the UV-Vis spectrum; upon excitation to these low-energy (LMCT)-L-1 states, release of one N-3(-) ligand is facilitated, and on triplet formation, the dissociation of both NH3 and N-3(-) groups trans to each other is promoted with no apparent reduction of the Pt-IV centre.