Synthesis, luminescent and multiple stimuli-responsive properties of π-extended BF2 β-diketone complexes containing an acridone unit

Abstract A class of π-extended BF 2 β-diketone chromophores, ADBF 2 -a and ADBF 2 -b, that containing electron donating N -butyl acridone units have been synthesized. ADBF 2 -a and ADBF 2 -b are highly fluorescent with quantum efficiencies (Φ F ) close to unity in toluene. The fluorescence of ADBF 2 -b displays more pronounced solvatochromism and shows a twisted intramolecular charge transfer (TICT) character in polar solvent and aggregation induced emission enhancement (AIEE) behavior. Furthermore, ADBF 2 -b shows high contrast and sensitive acid/base induced emission “On/Off” switching that result from the reversible protonation/deprotonation of the nitrogen atom. The compounds are also highly luminescent in solid state with a Φ F value of 0.63 for ADBF 2 -a and 0.28 for ADBF 2 -b. Single crystal analysis reveals the highly rigid and planar backbone of ADBF 2 -a. The emission stimuli-responsive properties of the compounds in solid state have been investigated. ADBF 2 -a shows yellow emission ( λ em  = 564 nm) in crystalline state while turned to be orange ( λ em  = 586 nm) after grinding. Intriguingly, CH 2 Cl 2 vapor fuming of the ground solid led to red emissive ( λ em  = 624 nm) solid, which turned to original yellow color with further CH 2 Cl 2 vapor fuming. The solid of ADBF 2 -b emits red ( λ em  = 645 nm) fluorescence in crystalline state and red-shifted to λ em  = 680 nm for amorphous solid after mechanical grinding. The crystalline state was recovered by CH 2 Cl 2 vapor fuming. We believe that this BF 2 system will inspire the development of high luminescent solid-state materials, and provide important insights into smart stimuli-responsive properties.