Studies on optical properties of N,O-Chelated azine-enol boron complexes featuring different fusion patterns of aromatic rings in the azine fragment

A series of N,O-chelated azine-enol boron complexes featuring four different fusion patterns between the benzene and pyridine rings of the azine fragment was synthesized and characterized. The optical properties of the corresponding complexes have been assessed in dichloromethane solution and in solid state. In the latter case the assessment was performed for both powder samples as well as batches of single crystals allowing to identify several cases of mechanochromism and one case of polymorphism-dependent emission. The correlations between the type of crystal packing and the emission strength of the crystalline samples have been pointed out.