Synthesis and properties of tetra-aryl azobispyrroles

The chemistry of the azobispyrrole framework, which melds the impressive electronic capabilities of the azo (-NN-) moiety and the pyrrole heterocycle, is significantly under-developed. Herein, the synthesis and characterisation of a series of azobispyrroles substituted with four aryl groups are presented. The steric bulk of aryl groups at the β-positions of the pyrrolic building blocks controls the degree to which azobispyrrole formation competes with aza-dipyrrin formation when using nitrobutanones as starting materials. The ability of aryl groups at the α-positions of the pyrrolic building blocks to influence conformational stability is discussed, as is the consequent control of photophysical properties.