Nonlinear Optical Response Properties of Aryl - Substituted Boron -Dipyrromethene Dyes: Unidirectional Charge Transfer coupled with Structural Tuning

摘要

Controlling the nonlinear optical (NLO) response properties at the molecularlevel is a key to develop strong NLO active materials for technologicalapplications. In this paper, we report quantum chemical investigation of NLOresponse properties of select aryl-substituted Boron-Dipyrromethene (BODIPY)dyes, a class of intramolecular charge transfer (ICT) probes. Densityfunctional theory (DFT) with long-range corrected CAM-B3LYP functional andcc-pVTZ, 6-31G(d,p) and 6-31+G(d,p) basis sets are employed to compute theelectronic structures and NLO response of the aforesaid molecules. Calculationsat the second order M{\o}ller-Plesset perturbation (MP2) level of theory areperformed for comparison. The results suggest that the charge transfer processin these molecules is mostly unidirectional and the total firsthyperpolarizability (\b{eta}total) values of these molecules are dominantlydictated by the response in the direction of charge transfer. Alteration ofconjugation strength through donor/acceptor substitution as well as twisting ofthe phenyl ring obtained through incorporation of methyl groups affect the NLOresponse of thesemolecules. The vector components of first hyperpolarizability(\b{eta}vec) of the probe molecules are also studied to analyze the anglebetween the vector components of \b{eta}vec and the dipole moment vector. Theresults presented here are expected to shed light on the origin of NLO responseof several aryl-substituted BODIPY dyes and provide means to optimizing it forfuture technological applications.