Study of organic dyes with a benzothiadiazole-dithienosilole central core as sensitizers in photoelectrochemical cells for hydrogen generation

In this work, we report the design and synthesis of two new organic D-A-π-A dyes endowed with a common benzothiadiazole-dithienosilole (BTD-DTS) central core, and their evaluation as anodic sensitizers in dye-sensitized photoelectrochemical cells (DS-PEC) aimed at molecular hydrogen generation. Both dyes possess a cyanoacrylic acid as acceptor/anchoring group, but present two distinct donor groups bearing substituents of different hydrophilicity. Preliminary density functional theory (DFT) computational investigations indicated that the dyes presented the correct electronic structure and energy levels alignment for their desired application in devices. The compounds were then prepared by means of a concise synthetic sequence featuring a microwave-assisted Stille-Migita cross-coupling as the key step. Following their full spectroscopic and electrochemical characterization, the dyes were then employed to sensitize the nanocrystalline TiO2- or SnO2-based photoanodes of three-electrode DS-PECs, and the corresponding performances in terms of photocurrent production and hydrogen generation, as well as electrode stability, were assessed under several different conditions.