Excitation‐Dependent Quadruple‐Level Emission from an Isolated Molecule for Dynamic Information Encryption
Yibo Shi, Lin Liu, Wei‐Hai Fang, Qian Wang, Xiao Liu, Kai Feng, Wei Sun, Dongpeng Yan, Xuebo Chen
Abstract
Stimuli-responsive single-molecule multi-emission materials have long attracted considerable attention due to their great potential in non-phase-separated smart luminescence. Here, a new strategy is demonstrated for manipulating electron transfer based on donor-acceptor decoupling to regulate energy levels, aiming to achieve excitation-dependent (Ex-De) single-molecule emission with switchable multiple fluorescence and phosphorescence. The synthesized 10-phenyl-10H,13'H-spiro[acridine 9,6'-pentacen]-13'-one (ACRSP) exhibits anti-Kasha quadruple-level emission and opposite Ex-De afterglow in different environments. The high-energy emission bands of multi-fluorescence in solution respond to excitation, whereas in poly(methyl methacrylate) (PMMA), phosphorescence-fluorescence multi-emission causes Ex-De to appear in the low-energy emission band. Experimental and computational results indicate that exciton spin ratios and emissive state compositions vary with excitation modes, leading to dual Ex-De behavior from three fluorescence and one phosphorescence emissions. Donor-acceptor decoupling separates locally excited (LE) and charge transfer (CT) states, while triplet level inversion enables Ex-De behavior and room-temperature phosphorescence (RTP) coexistence (τ = 770.54 ms). By tuning the excitation mode of ACRSP, we achieve Ex-De long afterglow emission from an isolated molecule, enabling time-resolved and excitation-responsive multi-dimensional information encryption. This work offers design guidelines for purely organic Ex-De systems and paves the way for next-generation single-molecule responsive luminophores.