CEE-active red/near-infrared fluorophores with triple-channel solid-state “ON/OFF” fluorescence switching

Abstract

A class of beryllium complexes has been synthesized. These complexes display crystalline-enhanced emission (CEE) and exhibit morphology-dependent dark and bright red/NIR fluorescence. They show bright red/NIR emission in the crystalline form (λ_em: 635–700 nm; Φ_f: 0.27–0.40) and faint emission in the amorphous state. Their emission can be smoothly switched “ON” and “OFF” by simple grinding/solvent annealing processes. In addition, these complexes show interesting acid/base vapor induced fluorescence switching properties due to the amino groups of the ligands. Furthermore, the molecular packing modes of these complexes can be altered by heating and recovered by solvent annealing accompanied by fluorescence switching between dark and bright states. The first example of reversible triple-channel solid-state fluorescence “ON/OFF” switching realized through simple approaches of grinding/solvent annealing, acid/base vapor fuming, and heating/solvent annealing might have great significance on designing novel organic materials as chemical sensors.