Symmetric dicyanobenzothiadiazole (DCBT) dyes with a 1.5 eV excited state reduction potential range

Abstract

Strong molecular photooxidants are important in many disciplines including organic synthesis and renewable energy. In these fields, strongly oxidizing chromophores are employed to drive various transformations from challenging bond formations to energy storage systems. A range of photooxidant strengths are needed to drive these processes. A series of 8 symmetrically bisarylated 5,6-dicyano[2,1,3]benzothiadiazole (DCBT) dyes were studied for their tunability toward breadth of light absorption and photooxidant strength. The dye oxidation strength and light absorption tunability is the result of appending various aryl substituents on the periphery of the DCBT core which shows remarkable tunability of the final chromophore. The dyes are studied via steady-state absorption and emission, time-correlated single photon counting, computational analysis, and cyclic voltammetry. In changing the peripheral aryl substituents via electronics, sterics, and π-conjugation length, a series of dyes are arrived at with a dramatic 1.5 eV range in oxidizing strength and >200 nm (0.95 eV) absorption maxima tunability. Furthermore, two dyes in the series exhibit strong oxidizing strength while still approaching red light absorbance (>650 nm onset) which provides unique opportunities for the use of lower energy light to affect chemical transformations. Ultimately, this series provides options for photooxidations that allow for energetic tuning and selectivity for a given chemical transformation.