Methylenepyran based dipolar and quadrupolar dyes: Synthesis, electrochemical and photochemical properties

摘要

This paper presents the synthesis of a series of push-pull and quadrupolar π-conjugated structures incorporating pro-aromatic methylenepyran electron-donor groups and various electron-attracting groups. Some of the methylenepyran derivatives were oxidized by I_2 to give, after reduction by Na_2S_2O_3, bismethylenepyran compounds via successive steps. The electrochemical redox properties of methylenepyrans 5-9 and extended bismethylenepyrans 10, 14, and 15 determined by cyclic voltammetry indicate the formation of redox bistable systems with high bi-stability. Oxidation of the dimers obtained from 5 to 9 was also described. All compounds are colored and slightly fluorescent (except some bismethylenepyran derivatives). Some compound second-order nonlinear optical properties were investigated, and large positive values of μβ were obtained. A positive dimer effect was also observed for bispyran derivatives.