Polymerization‐Enhanced Intersystem Crossing: New Strategy to Achieve Long‐Lived Excitons

: For a singlet-triplet coupled molecular system, the efficiency of forward and reverse intersystem crossing processes can be enhanced by reducing the energy gap between the singlet and triplet excited states (ΔEST ), thus prolonging the exciton lifetimes. This has been proven beneficial for many emerging applications such as molecular luminescence, optoelectronics, and photonics. Here, a strategy is proposed to create small ΔEST by polymerizing fluorescent dye molecules, the efficacy of which is justified by density functional theory calculations and ultrafast spectroscopy. Thus, singlet-triplet exciton communication through polymerization-enhanced intersystem crossing is also proposed.