Control of aggregation-induced emission versus fluorescence aggregation-caused quenching by bond existence at a single site in boron pyridinoiminate complexes

This manuscript reports the control of the luminescence properties of organoboron complexes between fluorescence aggregation-caused quenching (ACQ) and aggregation-induced emission (AIE) with or without a chemical bond at a single site in the pyridinoiminate skeleton. Novel boron complexes with (FBPI) and without (BPI) the fused structure in the ligand moiety were designed and synthesized. From the optical measurements, it was demonstrated that their solution- and solid-state emission behaviors oppositely varied with the presence of the fused structures. FBPI showed critical ACQ in a poor solvent. In contrast, BPI presented AIE behaviors. Additionally, from further evaluation of the solid-state emissive properties, it was shown that both boron complexes had crystallization-induced emission enhancement (CIEE) properties. Finally, it was demonstrated that reversible regulation of the emission intensity by external stimuli such as heating and solvent vapor fuming was accomplished with BPI based on the CIEE properties.