Water-directed self-assembly of a red solid emitter with aggregation-enhanced emission: Implication for humidity monitoring

Abstract

Advances in sensors benefit tremendously from the stimuli-responsive self-assembly technique. Aggregation-induced emission (AIE) and Aggregation-enhanced emission (AEE) luminogens have emerged as reliable building blocks for optical sensor as they overcome many of the limitations of conventional fluorescent probes. In this report, we describe the first synthesis and photophysical properties of DBIA, a donor-acceptor (D-A) type AEE luminogen with red solid-sate emission. It shows stimuli-responsive self-assembly behavior upon fumigation with water steam. Our systematic investigation using microscopy has observed various supramolecular architectures with different relative humidity (RH) values at room temperature (25 °C), including rough-surfaced flocs structure (RH = 20%), nanorods (RH = 60%) and rectangular stratified microsheets (RH = 85%). In addition, there is a sharp increase in emission intensity when DBIA molecules are assembled in the presence of water steam, as the AEE mechanism is further reinforced in this case. Hydrogen bonding between DBIA and water molecule was detected by dynamic spectral analysis, and further proved by DFT calculation. Thus the mechanism for the stimuli-responsive self-assembly toward water and the consequent emission enhancement is illustrated. Taking advantage of the water-sensitivity, a water sensor was developed, affording a detection limit of 2.64 mM as a liquid water probe, and RH 22.5% as a humidity sensor. It also shows fast response, easy visualization, broad detection region and the capacity of resisting disturbance.