Achieving long lifetime of pure organic room-temperature phosphorescence via constructing hydrogen-bonded organic frameworks

Metal-free pure organic room-temperature phosphorescence (ORTP) materials have attracted widespread attention in the fields of information security, optoelectronics and displays. Hydrogen-bonded organic frameworks (HOFs) can potentially stabilize the triplet excitons and achieve highly efficient RTP. However, it is still a tough challenge to prepare HOFs with ultra-long lifetime RTP. Herein, we report a facile and green hydrothermal method to synthesize rigid melamine-cyanuric acid (M-CA) supramolecular frameworks by a melamine hydrothermal reaction. The luminescence properties of M-CA supramolecular HOFs have been explored under ambient conditions for the first time. There are three modes of luminescence under ambient conditions, including prompt fluorescence, delayed fluorescence (DF) and RTP. The M-CA material shows a long RTP lifetime of 864.1 ms, which is over 7000 times longer than that of melamine itself. The effective intermolecular interactions suppress nonradiative transition of the triplet excitons, enhance the intersystem crossing and provide an oxygen-insulated environment, thus boosting RTP emission. In addition, due to dual emission properties of RTP and fluorescence, the obtained M-CA supramolecular HOFs can be potentially applied in the field of information encryption.