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Triplet Harvesting Using Two-Photon Absorption in Substituted Naphthalimides for Their Application as Heavy-Atom-Free Photosensitizers

Samanta, Pralok K., English, Niall J.
Journal of physical chemistry 2020 v.124 no.15 pp. 8178-8185
density functional theory, fluorescence, neoplasm cells, neoplasms, photochemotherapy, photosensitizing agents
The role of photodynamic therapy (PDT) in cancer treatment arises due to its specificity and sensitivity for tumor cells. For a series of thiocarbonyl-naphthalimide derivatives of potential PDT interest as heavy-atom free photosensitizers, optical (one- and two-photon) absorption, and fluorescence properties, along with intersystem-crossing rates, have been estimated by density-functional theory (DFT) and time-dependent DFT (TD-DFT). Absorption and fluorescence energies and intersystem crossing rates agreed well with the available experimental data. Our results predict that the effective intersystem crossing for conventional naphthalimides occurs as ¹π–π* → ³n–π*; the crossing channel for thiocarbonyl naphthalimides is ¹n–π* → ³π–π*. The latter, with nonradiative S₁ state, transforms to the triplet state via an intersystem crossing. Encouragingly for photosensitizer “prospecting”, both conventional and thiocarbonyl naphthalimides exhibit strong two-photon absorption (TPA) in the near-infrared region at ∼696–1092 nm; we predict that combining both TPA and superior intersystem crossing renders naphthalimides as ideal PDT photosensitizers.