Optical properties of porphyrin analogues for solar cells: An NLO approach

The geometries, electronic structures, and optical properties of various β-substituted Zn tetraarylporphyrin analogues were studied using density functional theory (DFT). Major differences in geometry and electronic properties were observed as a function of the acceptor moiety. Analogues containing cyanoacrylic acid had longer Zn–N21 bonds, narrower band gaps, and more stabilized energy levels than their methylenemalonic counterparts. Nonlinear optical (NLO) properties were calculated using the Finite Field approach; they were influenced by the strengths of the donor and acceptor moieties and the length of the π-spacer group. The NLO response for all analogues was dominated by only one tensor component, indicating unidirectional charge transfer. The NLO results correlated well with the observed photo-to-current efficiencies provided that the analogues in comparison have the same π-conjugation length.