Aryl-Substituted Boron Subphthalocyanines and their Application in Organic Photovoltaics

Abstract

A family of five axial aryl-substituted boron subphthalocyanine (BsubPc) derivatives bearing a hydrido, methyl, methoxy, phenyl, or fluoro substituent at the para position of the aryl were synthesised from Br-BsubPc and the corresponding aryl Grignard reagent in moderate yields. The physicochemical characterisation of these derivatives gave similar absorption, photoluminescence, and cyclic voltammetry profiles and photoluminescence quantum yields, indicating that the nature of the substituent at the para position does not influence the basic photophysical properties of this generic class of BsubPcs. Conversely, the solid-state structural arrangement obtained from single crystals is highly dependent on the para substituent; for the non-polar hydrido, methyl, and phenyl substituents, only concave isoindole π interactions are present. Substitution for the polar methoxy or fluoro ligand affords one-dimensional ribbons formed by convex π interactions, where these ribbons further interact through concave isoindole π interactions with the adjacent ribbon, creating an extended two-dimensional π network. On incorporation of the hydrido, methyl, and fluoro derivatives into organic photovoltaic (OPV) devices, similar results and device metrics were obtained with the methyl and fluoro derivatives. Both, however, were significantly outperformed by the hydrido derivative. The uniqueness of the hydrido derivative is only realised once incorporated into OPVs as it shares the same basic physical properties as the other derivatives. Given these findings, we identify the hydrido derivative as the aryl-BsubPc with the most promise for future work in OPVs.