Practical Design of 3,6-Di-tert-butyldiphenyldibenzofulvene Derivatives with Enhanced Aggregation-Induced Emission

Diphenyldibenzofulvene derivatives consisting of an aromatic tert-butyl-substituted fluorene stator and different rotors consisting of nonsubstituted phenyl groups (3,6-dtb-DPBF) and monomethyl-substituted (3,6-dtb-DPBFMe) and dimethyl-substituted [3,6-dtb-DPBF(Me)2] forms have been synthesized and found to display aggregation-induced emission (AIE). The incremental number of substituents from 3,6-dtb-DPBF to the 3,6-dtb-DPBFMe and 3,6-dtb-DPBF(Me)2 derivatives promotes significant changes, from a good solvent (acetonitrile, MeCN), where it is very poorly emissive, to thin films or aggregates, in MeCN/water mixtures, and a huge increment in fluorescence emission, which is found to be dependent on the water fraction, fw. The characteristics (size and distribution) of the aggregates were further corroborated with dynamic light scattering measurements. From time-resolved fluorescence experiments (TCSPC and FLIM), the increase in the contribution of the longer decay component is linked to the emission of the aggregate (AIE effect). To assist in the elucidation of the aggregation process at a molecular level, the data were complemented with computational studies [time-dependent density functional theory (TDDFT) and molecular dynamics (MD) simulations]. From MD, the octamer properly addresses the properties of the aggregate. As determined by the X-ray data, the crystal structure of a two-unit special disposition is identical to the geometry of the most stable structure obtained from MD and TDDFT calculations.