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.