Push–Pull NN-DiphenylhydrazonesBearing Bithiophene or ThienothiopheneSpacers as Nonlinear OpticalSecond Harmonic Generators and as Photosensitizers for NanocrystallineTiO2 Dye-Sensitized Solar Cells

摘要

A series of push–pull heterocyclic N,N-diphenylhydrazones were prepared to study the effect of structural modifications (different π-spacers and electron-withdrawing groups) on the optical (linear and nonlinear) and electronic properties of the molecules. The photovoltaic response of dye-sensitized solar cells assembled using nanocrystalline titania photosensitized with the synthesized dyes was also studied. These heterocyclic push–pull conjugated dyes involve N,N-diphenylhydrazones as electron donors linked to bithiophene or thieno[3,2-b]thiophene spacers and were functionalized with carboxylic acid, cyanoacetic acid, or dicyanovinyl acceptor groups. A combination of Suzuki–Miyaura cross-coupling, Vilsmeier formylation, and condensation reactions was used to synthesize the intermediates and final products. Density functional theory (DFT) and time dependent-DFT calculations were used to obtain information on conformation, electronic structure, and electron distribution, both for the free dyes and those adsorbed on TiO2. The results of this multidisciplinary study indicate that dyes >5b and >6b have the strongest second-ordernonlinear optical response with hyperpolarizability values in therange of β = 2330 × 10^–30 to 2750 ×10^–30 esu, whereas photovoltaic power conversionefficiencies reach values in the range of 0.7–3.0% for dyes >5a–b and >7c and were enhanced by coadsorbingdeoxycholic acid (0.8–5.1%).