07/2014

A collaborative project between the Marder and El-Sayed groups explores the effect of molecular variation in the performance of a series of D-A-Pi-A dyes, prepared through C–H functionalization, on their solar to electric power conversion efficiencies.

Organic solar dyes typically contain electron-rich (donor: D) and electron-poor (acceptor: A) regions connected by a conjugated bridge, with a recent advance being the inclusion of an auxiliary electron-withdrawing unit into the bridge to facilitate electron transfer.

This work builds upon the discovery that C–H Functionalization provides a direct and efficient method for the elaboration of the electron-withdrawing unit, the 5,6-difluoro-2,1,3-benzothiadiazole (DFBTD), leading to the construction of novel D-A-Pi-A sensitizers, incorporating a new bridging system based on the cyclopentadithiophene (CPDT) unit, the side-chains of which were designed to reduce dyeaggregation.

This work describes the synthesis and evaluation of four novel dyes, providing a clear picture of how the different molecule variations impact the efficiencies of these systems. Incorporation of the electron-withdrawing DFBTD unit and bridging CPDT led to a dye with a solar to electric power conversion efficiency of 9.1%.

Investigations are ongoing to explore the new electron deficient units that can be functionalized using C–H activation, typically a difficult reaction using more conventional cross-coupling technologies.