Quadratic nonlinear optical response in partially charged donor-substituted tetrathiafulvalene: From a computational investigation to a rational synthetic feasibility

摘要

A computational (ZINDO) investigation is employed to estimate the molecular hyperpolarizability (beta) of a [(TTF-NH2)(8)] (TTF = tetrathiafulvalene) octameric stack at various fractional (0 < rho < 1) oxidation states of TTF rho+. While the neutral [(TTF-NH2)(8)] octamer exhibits a modest (7.6 x 10(-30) cm(5) esu(-1)) static beta(0) value, in relation to a nearly centrosymmetric electronic structure, the formal (TTF-NH2)(0.25+) oxidation state leads to a giant (beta(0) = 3891 x 10(-30) cm(5) esu(-1) per octamer) NLO response. This effect is related to the appearance of an extremely intense HOMO -> LUMO-based low-lying transition, occurring at 1260 nm upon fractional oxidation, thus providing new and unexpected interest in TTF-donor substituted molecules. To illustrate the chemical feasibility of such species, two kinds of derivatives are synthesized: a TTF-dimethylaniline (TTF-DMA) by using in particular a Suzuki cross-coupling reaction between iodo-TTF and p-dimethylaminophenylboronic acid and a TTF-vinyldimethylaniline (TTF-VDMA) by a Wittig-type condensation notably between TTF-carboxaldehyde and p-(dimethylamino)benzyltriphenylphosphonium bromide. Their NLO response, evaluated at 1.064 mu m by the Hyper Raleigh Scattering technique, leads to beta values around 240 x 10(-30) cm(5) esu(-1), in both cases. Additionally, these monomeric species are observed to exhibit very strong multiphoton fluorescence in solution after one electron oxidation. Different routes are discussed toward a possible engineering of TTF-donor based chromophores into oligomeric stacks in the solid state.