Synthesis, redox and quadratic nonlinear optical properties of novel thienylpyrrole derivatives containing pyridinium electron-acceptor group

摘要

Quaternized pyridine derivatives have attracted interest for many years from variousperspectives, especially for potential applications in electronic/optical devices.1 Pyridiniumsalts are readily synthesized, highly stable, and often combine intense visible absorptions withreversible electrochemistry. Notable recently proposed applications of these compounds rangefrom advanced telecommunications to fluorescent probes for bioimaging.2 As part of an ongoingprogram to develop strong charge transfer donor-acceptor thienylpyrrole systems withenhanced nonlinear optical (NLO) properties3 we have explored the potential of pyrrole 4 andthienylpyrrole-based chromophores 5-6 as efficient π-electron donor moieties functionalizedwith N-methylpyridinium acceptor group substituted at thiophene or pyrrole rings (Figure).Compounds 4-6 were prepared, in good yields, through Knoevenagel condensation of theprecursor pyrrole 1 or thienylpyrrole 2-34 aldehydes with 1-methylpyridinium salt. On theother hand, formyl-pyrroles 1 were prepared through Paal-Knorr synthesis followed byVilsmeier formylation. The molecular structure, especially the degree of planarity and therelative orientations of the auxiliary donor and acceptor entities, is found to strongly influencetheir electrochemical and NLO properties. In this communication we report on the synthesis,redox properties, thermal stability and first order nonlinear optical hyperpolarizabilities forthe novel cationic chomophores 4-6. These results indicate that these compounds have good