DFT/TD-DFT studies on structural and spectroscopic properties of metalloporphyrin complexes: A design of ruthenium porphyrin photosensitizer

Given their efficacy in photosynthesis, a series of metalloporphyrins were examined using density functional theory (DFT) and time-dependent DFT. An experimentally known zinc porphyrin has been calculated to evaluate performance of various functionals, basis sets, computational models of solvent effect and solvent sorts. With an alternative approach, absorption spectra of complexes (MLx, M = Zn, Cd and Hg, x = 1–4) varying substituted porphyrin Lx and metal center were investigated. It was shown that the strongest peak at about 400 nm for MLx was attributed to the intra-porphyrin π → π* transition. Substitution of benzoic acid at the β-position of porphyrin core allows an extra intense peak at 450 nm in ML3 and ML4, but ML2 with the meso-substituted benzoic acid only displays some very weak low-energy absorptions. Additionally, we theoretically designed [Ru(NCS)2Lx]2− and expected their possession of advantages of polypyridyl ruthenium and porphyrin-based sensitizers. The present study reveals that the L4 complex, [Ru(NCS)2L4]2−, exhibits extra intense absorption peaks at 500 and 582 nm, allowing for its promising application in dye-sensitized solar cells (DSSCs).