Abstract: Polymers are routinely used as embedding matrices for organic molecular phosphors to substantially reduce the non-radiative decay rate and promote room-temperature phosphorescence (RTP). However, most previous studies focus on how glass transition temperature and free volume of various polymers influence RTP efficiency; very little is known on how electronic coupling between the matrix and the phosphor can modulate organic RTP. In the current investigation, we attempt to address the issue by synthesizing a monomeric version of an aromatic ketone phosphor and copolymerizing the ketone with four different types of matrix monomers. The resulting copolymers exhibit clear matrix-dependent RTP efficiency: a gradual decrease of RTP quantum yield from 22% to nearly 0 can be observed when the electronic conjugation of the matrix increases, suggesting that energy dissipation can occur in the triplet excited state via electron exchange when the triplet state of the matrix is close to that of the phosphor. The study provides a guiding principle on regulating the lifetime of triplet-excited states for organic dyes.