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.