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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.