Theoretical Study on Static Second Hyperpolarizabilities for Several π-Conjugated Systems Including Nitrogen Atoms: Effects of Charged Defects and Extension of π-Conjugation

摘要

We investigated static second hyperpolarizabilities (γ) of 1,4-phenylendiamine (PDA) and 4,4'-diaminodiphenylamine (DADPA) by using the ab initio molecular orbital (MO) methods. The DADPA molecule is assumed to have a planar structure, in which two PDA are linked by a central nitrogen (N) atom, and is considered to be the simplest model for extended dendrimers including linking N atoms. We also examined dicationic PDA and DADPA in order to clarify the effects of charged defects in π-conjugated systems on γ values. The γ value is shown to be enhanced nonlinearly by linking two π-conjugated units via an N atom. It is also found that the introduction of positive charges causes not only the change in the sign of γ but also a significant enhancement of the magnitude. Judging from the present results, the extended dendrimers involving linking N atoms are expected to exhibit significantly large values due to an extension of -conjugation, and the introduction of positive charges is further predicted to cause drastic changes both in sign and magnitude of their γ values.