Two polymorphs of a tetraphenylethene-substituted aza-borondiquinomethene complex and their emissions in different molecular packings

Multi-color emission materials with unique molecular stackings in aggregated states have attracted great attention. To better understand the relationship between emission properties and co-assembling systems, we report herein a novel aza-borondiquinomethene complex (TAB) bearing tetraphenylethene substituents at the 4,4′-positions of its central core. This system was found to crystallize in two polymorphs with different molecular stackings. TAB (G) exhibits weak green emission (λ_em = 500 nm, Φ = 6.0%) due to a strong π-π interaction, whereas TAB (Y) exhibits a much brighter yellow emission (λ_em = 550 nm, Φ = 52.0%). The different molecular stackings gave rise to the interesting emissions, and these unusual emission phenomena were rationalized by Hirshfeld surface analyses and theoretical calculations. This research may broaden the scope for the design of multi-color emission materials adopting different aggregation states.