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

Abstract

Three heterocyclic dyes were synthesized having in mind the changes in the photovoltaic, optical and redox properties by functionalization of 5-aryl-thieno[3,2-b]thiophene, 5-arylthiophene and bis-methylpyrrolylthiophene π-bridges with different donor, acceptor/anchoring groups. Knoevenagel condensation of the aldehyde precursors with 2-cyanoacetic acid was used to prepare the donor-acceptor functionalized heterocyclic molecules. These organic metal-free dyes are constituted by thieno[3,2-b]thiophene, arylthiophene, bis-methylpyrrolylthiophene, spacers and one or two cyanoacetic acid acceptor groups and different electron donor groups (alkoxyl, and pyrrole electron-rich heterocycle). The evaluation of the redox, optical and photovoltaic properties of these compounds indicate that 5-aryl-thieno[3,2-b]thiophene-based dye functionalized with an ethoxyl electron donor and a cyanoacetic acid electron acceptor group/anchoring moiety displays as sensitizer for DSSCs the best conversion efficiency (2.21%). It is mainly assigned to the higher molar extinction coefficient, long π-conjugation of the heterocyclic system, higher oxidation potential and strong electron donating capacity of the ethoxyl group compared to the pirrolyl moiety.

Azaphosphinines and their derivatives

“…Simple five- and six-membered nitrogen-containing ring systems such as pyrrole, piperidine, and pyridine commonly act as solvents and/or bases in synthetic processes as well as fundamental building blocks to all manner of pharmaceuticals, dyes, ligands, and pesticides. 2–12 In comparison to their 2nd row counterparts, phosphorus heterocycles are considerably less common in the literature. However, this is not to say that these molecules do not find important uses in the modern world.…”

New organic dye-sensitized solar cells based on the D–A–π–A structure for efficient DSSCs: DFT/TD-DFT investigations

“…60–64 For DSSCs, several electron-acceptor materials have been developed and synthesized. 65–67 However, cyanoacrylic acid is often employed as an electron-acceptor material due to its high electron-attracting capacity and solid binding to the TiO 2 surface, which facilitates electron injection. 68 The selection of the π-spacer is critical when designing D–π–A dyes because it plays a crucial function in regulating the HOMO–LUMO energy levels and expanding the absorption range of organic sensitizers.…”

Recent advances on visible light pyrrole-derived photoinitiators of polymerization

“…Pyrrole is a heterocyclic five-membered ring compound in which the involvement of the lone pair electrons of nitrogen to the aromaticity of pyrrole makes this heterocycle an excellent electron donating group when combined with the appropriate group. Pyrrole is extensively used in Organic Electronics for the design of semiconductors for organic field effect transistors, [230,231] as active layers for organic photovoltaics, [232][233][234], for the design of dyes with solvatochromic properties, [235] the design of dyes with non-linear optical properties [236][237][238][239] or electrochromes. [240] Recently, pyrrole was investigated in the photopolymerization field and used as an elemental building block for the design of dyes of various structures.…”

“…Pyrrole is also an excellent electron donor so that push-pull dyes could be designed with this heterocycle. [234,235,[243][244][245][246] Overall, even if numerous families of dyes have been tested as photoinitiators, easiness of synthesis, easy oxidation of pyrrole and the facile tunability of the absorption properties of the pyrrole-based dyes could make pyrrolebased photoinitiators, dyes of higher reactivity than the aforementioned families. Difference of rate constant of interaction with the different additives, more appropriate excited state lifetimes could enable pyrrole-based dyes to outperform to the other dyes.…”