Achieving Efficient Lifetime‐Tunable Room‐temperature Phosphorescent Cellulose with Excitation Wavelength‐ and Time‐Dependence

Abstract The precise modulation of the lifetime and the responsive properties of room‐temperature phosphorescence (RTP) is essential for realizing its multifunctional applications. Herein, a facile strategy is presented to achieve a series of cellulose benzoate esters (CBE‐X, X = H/CH 3 /OH/NH 2 ) with lifetime‐tunable RTP through substituent engineering. Enhancing the electron‐donating ability of CBE‐X effectively modulates the HOMO‐LUMO gap, exciton energy, spin‐orbit coupling, and interaction between cellulose chains, thereby enabling control over the RTP lifetime. The RTP lifetime of CBE‐X can be increased from the initial values of tens of milliseconds to over 1000 ms. Notably, the CBE‐NH 2 film with an electron‐rich substituent achieves an ultra‐long RTP lifetime of 1046 ms and a quantum yield of 53.42%. Furthermore, the aggregation of diverse clusters on cellulose chains endows these films with unique excitation wavelength‐ and time‐dependent afterglow, providing novel concepts for multidimensional dynamic optical coding. This study establishes the clear structure‐property relationship between substituent's electronic characteristics and RTP performance in cellulose‐based systems, providing both theoretical insights and a sustainable design paradigm for eco‐friendly phosphorescent materials.