Computational Study of Photochemical Relaxation Pathways of Platinum(II) Complexes

A series
of functional platinum­(II) complexes (Pt1–Pt3),
which present high activity in four-photon absorption, in vivo
imaging, and precise cancer therapy, as previously reported by the
experimental work of Zhang et al. (Inorg. Chem. 2021, 60, 2362–2371), are computationally investigated
in the article. We find that after the complex goes through four-photon
absorption to the S1 state, it undergoes intersystem crossing
to the T2 state and eventually reaches the T1 state through internal conversion. On the T1 state, both
radiative and nonradiative decay to S0 exit. The radiative
decay forms the basis for the phosphorescence imaging in tissues as
reported in the original paper. In addition, the nonradiative decay
can simultaneously generate cytotoxic singlet oxygen by the excited
energy transfer process, also known as triplet oxygen’s quenching
of triplet states. We conclude that the phosphorescence property as
well as the photosensitizer character jointly bring high activity
of in vivo imaging and photodynamic therapy to these complexes.