Nonlinear optical properties of highly conjugated push–pull porphyrin aggregates: Role of intermolecular interaction

We present a quantum-chemical analysis of porphyrin aggregates performed to provide insight into the intermolecular interactions and the relationship between their structural and collective non-linear optical properties. The first hyperpolarizabilities are evaluated for monomer and aggregates of a series of push–pull porphyrins, whose synthesis and hyperpolarizabilities are reported recently in literature [T.G. Zhang, Y. Zhao, I. Asselberghs, A. Persoons, K. Clays, M.J. Therien, J. Am. Chem. Soc. 127 (2005) 9710]. The molecular geometries are obtained via B3LYP/6-31G (d, p) level optimization including SCRF/PCM approach, while the dynamic NLO properties are calculated with the ZINDO/CV method including solvent effects. It has been observed that the first hyperpolarizability changes tremendously as monomer undergoes aggregation and the magnitude of first hyperpolarizabilities are highly dependent on the nature of aggregates. Importance of our results on the design of electro-optic materials has been discussed.