Loose Cocrystal Strategy for High-Efficiency Near-Infrared Phosphorescence

Harvesting triplet excitons of large & pi;-conjugate aromatic molecules via cocrystal engineering for attaining near-infrared (NIR) phosphorescence has aroused wide attention due to its fundamental significance and practical application. Herein, the pyrene (Py)-N, N'-bis(1-ethylpropyl)-2,5,8,11-tetrakis(p-methyl-phenyl)-perylenediimide (MP) organic cocrystal is designed and fabricated via the solution self-assembly method, which demonstrates the NIR phosphorescence with a maximum peak at 730 nm and a photoluminescence quantum yield of 34.2%. The singlet states with an intermediate energy level from MP molecules bridges singlet and triplet states of Py molecules, resulting in efficient NIR phosphorescence. Importantly, the loose packing pattern makes MP an excellent elementary molecule that can be assembled with a variety of aromatic molecules, from ternary to six-membered benzene rings and even larger benzene skeletons. In contrast to the limitations of traditional cocrystal systems, cocrystal engineering based on MP molecules with weak & pi;-& pi; interactions is no longer limited to the careful selection and collocation of molecular structures, uncertain assembly behavior, and unpredictable properties. This work holds considerable insights for the exploration of novel NIR phosphorescent materials via a universal strategy.