PDT-correlated photophysical properties of thienopyrrole BODIPY derivatives. Theoretical insights

• Photophysical properties of Thienopyrrole BODIPY Derivatives are computed.
• The electronic spectra show a Q band falling in the so-called therapeutic window.
• Spin-Orbit matrix elements suggest the bromine-substituted BODIPY as photosensitizer.

Absorption electronic spectra, singlet-triplet energy gaps and spin–orbit matrix elements of thienopyrrole BODIPY derivatives, recently synthesized and proposed as potential photosensitizers in photodynamic therapy (PDT), have been computed by means of density functional theory (DFT) and time-dependent DFT approaches. A benchmark on structural parameters and maximum absorption wavelengths of different exchange-correlation functionals in combination with two basis set has been performed. The singlet-triplet energy gaps found are consistent with their possible application in PDT. The investigated molecules possess two excited triplet states (T1 and T2) that lie below and approximately at the same energy of the excited singlet one (S1), respectively. Both the radiationless transitions between S1 and triplet states contribute to the intersystem spin crossing efficiency, which in turn increases the production of singlet oxygen. Comparing their properties with those of agents currently used in PDT, one of them could be potentially used as photosensitizer for singlet oxygen production.

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