Rational design of cyanovinyl-pyrene dual-emission AIEgens for potential application in dual-channel imaging and ratiometric sensing in living cells

Aggregation-induced emission luminogens (AIEgens) provide a new approach to address the aggregation-induced quenching (ACQ) defect prevalent in traditional fluorescent dyes. Since there are only two dispersion forms of single molecule (monomer state, weak fluorescence) and aggregates (multimer state, strong fluorescence) in aqueous medium, most of the reported AIEgens exhibit a single emission band and therefore cannot be used for dual-channel fluorescence imaging in living cells. In this work, the “monomer-dimer-multimer” dispersion mechanism was innovatively introduced into the design of dual-emission AIEgens. Under the guidance of this concept, two cyanovinyl-pyrene dual-emission AIEgens with twisted molecular configuration have been readily synthesized and studied by theoretical calculations, UV–visible absorption, steady-state fluorescence, time-resolved fluorescence, dynamic laser scanning (DLS) and laser confocal imaging. These AIEgens emit weak fluorescence in monomer state due to intramolecular C[sbnd]C rotation. With gradual aggregation, they form dimer state to emit blue fluorescence centered at 460 nm, and then convert into multimer state to emit red fluorescence around 570 nm, simultaneously exhibiting AIE and dual-emission characteristics. They also have excellent photostability, good membrane permeability and low cytotoxicity. Confocal imaging tests demonstrate that AIEgens composed of cyanovinyl-pyrene and benzimidazole moieties is available for dual-channel imaging in Hela cells and macrophages cells, and shows great potential in designing ratiometric nanoprobe. Our design mechanism will provide a versatile platform for the development of dual-emission AIEgens.