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

Abstract

A class of π-extended BF2 β-diketone chromophores, ADBF2-a and ADBF2-b, that containing electron donating N-butyl acridone units have been synthesized. ADBF2-a and ADBF2-b are highly fluorescent with quantum efficiencies (ΦF) close to unity in toluene. The fluorescence of ADBF2-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, ADBF2-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 ΦF value of 0.63 for ADBF2-a and 0.28 for ADBF2-b. Single crystal analysis reveals the highly rigid and planar backbone of ADBF2-a. The emission stimuli-responsive properties of the compounds in solid state have been investigated. ADBF2-a shows yellow emission (λem = 564 nm) in crystalline state while turned to be orange (λem = 586 nm) after grinding. Intriguingly, CH2Cl2 vapor fuming of the ground solid led to red emissive (λem = 624 nm) solid, which turned to original yellow color with further CH2Cl2 vapor fuming. The solid of ADBF2-b emits red (λem = 645 nm) fluorescence in crystalline state and red-shifted to λem = 680 nm for amorphous solid after mechanical grinding. The crystalline state was recovered by CH2Cl2 vapor fuming. We believe that this BF2 system will inspire the development of high luminescent solid-state materials, and provide important insights into smart stimuli-responsive properties.