Similar and different: Effect of substitution pattern on the aggregation-induced emission property of [4'-(bisphenylamino)[1,1']biphenyl] methylene fluorenes

Three isomers, [4 '-(bisphenylamino)[1,1 ']biphen-2-yl]methylenefluorene (BAB2MF), [4 '-(bisphenylamino)[1,1 ']biphen-3-yl]methylenefluorene (BAB3MF) and [4 '-(bisphenylamino)[1,1 ']biphen-4-yl]methylenefluorene (BAB4MF), were synthesized through Suzuki coupling. The substitution pattern exerts a dramatic influence on the optical property. BAB3MF and BAB4MF are hardly emissive either in the solution or as solid state. On the contrary, BAB2MF emits strongly, especially in the aggregate state with a high fluorescent quantum yield of 69%. Furthermore, BAB2MF shows an aggregation-induced enhanced emission behavior. BAB2MF solid emits at 488 nm, about 60 nm blue-shifted from its solution.