Abstract
Platinum azide complexes are appealing anticancer photochemotherapy drug candidates because they release cytotoxic azide radicals upon light irradiation. Here we present a density matrix renormalization group self-consistent field (DMRG-SCF) study of the azide photodissociation mechanism of trans,trans,trans-[Pt(N3)2(OH)2(NH3)2], including spin–orbit coupling. We find a complex interplay of singlet and triplet electronic excited states that falls into three different dissociation channels at well-separated energies. These channels can be accessed either via direct excitation into barrierless dissociative states or via intermediate doorway states from which the system undergoes non-radiative internal conversion and intersystem crossing. The high density of states, particularly of spin-mixed states, is key to aid non-radiative population transfer and enhance photodissociation along the lowest electronic excited states.
Highlights
Platinum azide complexes are appealing anticancer photochemotherapy drug candidates because they release cytotoxic azide radicals upon light irradiation
Platinum(IV) complexes,8−17 and in particular Pt(IV) azides,10,18−26 count among the first and yet most promising photoactivated drug candidates because they are stable in the absence of light and only upon light irradiation release highly cytotoxic products.26−28 their photoreaction pathways have been heavily investigated experimentally10,18,27−34 but less so computationally.35−38 understanding the major photoreaction pathway at the atomic level i.e., the dissociation of the azide ligands that recombine to nitrogen along with the reduction of the metal center to Pt(II)17 remains elusive
Density matrix renormalization group (DMRG)based methods,43−47 including that with self-consistent field (DMRG-SCF),48,49 are ideally suited for multiconfigurational studies of transition metal complexes, as they allow for significantly larger active orbital spaces than traditional multiconfigurational methods
Summary
Platinum azide complexes are appealing anticancer photochemotherapy drug candidates because they release cytotoxic azide radicals upon light irradiation. We calculated unrelaxed potential energy curves of the lowest 11 singlet and 9 triplet (spin-free) states along the Pt−N3 bond (see Figure 3).
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