Electronic Properties of a New Photosensitizer-Dye Derived from a Cadmium Selenide Mediated Retinoid/Carotenoid-Based Complexes of Rhenium (I)

Two new inorganic-based photosensitizer dyes of rhenium(I) attached to retinoid/carotenoid ligands have been synthesized. All ligands were prepared via Knoevenagel condensation reactions of all-trans-retinal (1) and β-apo-8’- carotenal with cyanopyridyl. Electronic UV/Visible absorption spectroscopy shows that these complexes absorb visible light efficiently. Absorption wavelengths are in the 450 nm to 600 nm range. Density Functional Theory (DFT) calculations reveal that the frontier molecular orbitals involved during absorption process occur from the HOMO (highest occupied molecular orbital) to low-energy LUMOs (lowest unoccupied molecular orbital) of the Re metal center. Theoretical treatments also show that these orbitals are located primarily on the polyene chain and the energy gap between them is consistent with the observed optical spectrum. The photosensitizer complexes will be attached to cadmium selenide (CdSe) nanoparticles for enhanced photosensitization