Excitation-Dependent Quadruple-Level Emission from an Isolated Molecule for Dynamic Information Encryption.

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.