Multi-Stimuli Responsive and Multicolor Adjustable Pure Organic Room Temperature Fluorescence-Phosphorescent Dual-Emission Materials

A simple bromine and cyanogen substituents positional isomeric 9-phenyl-9H-carbazole (PhCz) donor-acceptor system (namely p-NN-Br and m-NN-Br) displays ultralong organic phosphorescence, and exhibits unique dual emission properties (fluorescence and phosphorescence). These molecules are found to display distinct responses toward multiple external stimuli including temperature (T), excitation light intensity (I) and pressure (P), and show multicolor tunable behaviors (including the white light, the Commission Internationale d'Eclairage (CIE) = 0.33, 0.34). The unique stimuli-triggered proportion between singlet and triplet excitons for p-NN-Br and m-NN-Br is demonstrated systematically by investigating the photophysical spectrum, scanning electron microscope (SEM) imaging and X-ray analysis, coupled with theoretical calculations. They reveal that the simultaneous introduction of halogens (Br) and pseudohalogens (CN) to the PhCz skeleton can improve the intermolecular interaction and thermal stability. Single crystal analysis shows that there are many more types of dimers and J-aggregates, thereby stabilizing the excitation of triplet states. Moreover, these isomers have "latent" fingerprint recognition and anti-background interference performance, which is expected to provide a new method for fingerprint identification. All in all, this strategy paves the way to a multifunctional platform for the development of multi-stimuli responsive, multicolor regulation and smart luminescent materials with long-lived emission at room temperature.