Divergent Synthesis and Crystal Engineering of Room-Temperature Phosphorescent Carbonyl-Bridged Triphenylamines

Organic materials with room temperature phosphorescence (RTP) are a growing research topic, with recent investigations revealing a strong effect of the crystal packing on the RTP properties. However, these relationships are difficult to decipher, as the crystal packing affects both the intermolecular interactions and the molecular conformation. Here, we report a divergent synthetic strategy to generate a family of rigid carbonyl-bridged triphenylamine (TPA)-based chromophores via metal-free transformations of the same starting material, and exploit this family to investigate the effects of crystal packing on the solid state RTP properties. The minor bridge modifications lead the TPA derivatives to adopt three distinct crystal packing motifs: parallel columnar stacks, antiparallel zigzags, and nonparallel dimerized arrangements. Despite the nearly identical RTP spectra across the series, the proportion of phosphorescence in their emission and the RTP lifetimes are shown to differ as a result of the different crystal motifs. Computational investigations of dimer models of the solid state reveal that the interplay between fluorescence and triplet formation can be modelled by identifying the aggregate character of dimers in the crystal, but only if pairs in multiple dimensions of the crystal are considered.