Push–Pull N,N-Diphenylhydrazones Bearing Bithiophene or Thienothiophene Spacers as Nonlinear Optical Second Harmonic Generators and as Photosensitizers for Nanocrystalline TiO₂ Dye-Sensitized Solar Cells

Abstract

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-order nonlinear optical response with hyperpolarizability values in the range of β = 2330 × 10–30 to 2750 × 10–30 esu, whereas photovoltaic power conversion efficiencies reach values in the range of 0.7–3.0% for dyes 5a–b and 7c and were enhanced by coadsorbing deoxycholic acid (0.8–5.1%).

Push-Pull Heterocyclic Dyes Based on Pyrrole and Thiophene: Synthesis and Evaluation of Their Optical, Redox and Photovoltaic Properties

“…Thin-layer chromatography visualization under Ultraviolet-Visible UV light was used to monitor the reaction progress. The purification using silica gel chromatography and the characterization of the dyes, through melting point data, Nuclear Magnetic Resonance (NMR) and UV-visible spectra as well as the study of the redox properties, were obtained as described elsewhere [46,47,50,73].…”

“…General Procedure for the Synthesis of Precursor 1 Through Suzuki-Miyaura Cross-Coupling 2,5-Dibromothiophene (0.241 g, 1.0 × 10 −3 mol) was coupled with 1-methyl-1H-pyrrol-2-yl)boronic acid pinacol ester (0.580 g, 2.4 × 10 −3 mol), in a mixture of 1,2dimethoxyethane (DME) (8 mL), ethanol (2 mL), aqueous 2 M Na2CO3 (1.7 mL) and Pd(PPh3)4 (0.029 g, 3 mol%) at 85 °C under nitrogen. The reaction time (24 h) was Taking into account our knowledge on the modification of electrochemical, optical and photovoltaic characteristics of push-pull molecules through the auxiliary electron acceptor or donor effect of heterocycles [39][40][41][42][43][44][45][46][47][48][49][50], as well as previous studies reported by other groups [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][33][34][35][36][63][64][65][66][67][68][69][70], we are expanding the research to the preparation of three thiophene and pyrrole-based donor-acceptor heterocyclic molecules. The novel push-pull dyes are constituted by 5-aryl-thieno[3,2-b]thiophene, 5-arythiophene and bismethylpyrrolylthiophene π-bridges, with one or two cyanoacetic acid anchoring groups, and different electron-donor moieties (ethoxyl and pyrrole electron...…”

“…It is also well known that the position of the heterocyclic nuclei on the π-spacers is an important factor. Both types of heterocycles, electron-rich, such as thiophene and pyrrole, and electron-deficient, such as azole and azine derivatives, i.e., (benzo)thiazole benzothiadiazole, pyridine, etc., can act simultaneously as π-bridges and electron donors or acceptors, respectively [37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53].…”

“…Earlier, we have communicated the synthesis and application of heterocyclic pushpull sensitizers for DSSCs with several combinations of π-spacers, electron donor and acceptor/anchoring moieties (Figure 1) [46][47][48][49][50]. Taking into account our knowledge on the modification of electrochemical, optical and photovoltaic characteristics of push-pull molecules through the auxiliary electron acceptor or donor effect of heterocycles [39][40][41][42][43][44][45][46][47][48][49][50], as well as previous studies reported by other groups [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][33][34][35][36][63][64][65][66][67][68][69][70], we are expanding the research to the preparation of three thiophene and pyrrole-ba...…”

Synthesis of aryl-substituted thieno[3,2-b]thiophene derivatives and their use for N,S-heterotetracene construction

“…The thieno[3,2- b ]thiophene (TT) unit is highly demanded in modern organic synthesis since TT-based compounds have a variety of applications, e.g., in the field of organic electronics. Indeed, TT-based polymers and small molecules are used as light-harvesting dyes for dye-sensitized solar cells [1], electron-donating materials for bulk heterojunction solar cells [2–4], and p-type semiconductors for organic field-effect transistors [5–7]. Within the same context of organic semiconductor development, the bicyclic TT subunit has been used to architect various ring-fused S-heteroacenes, which have been studied extensively [8–10] due to their better characteristics compared to heteroatom-free acenes.…”