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Ultralong organic phosphorescent (UOP) materials without any metal species have broad application prospects in optical technologies and biological imaging due to the low cost and biocompatibility. However, it is still a challenge to prepare new UOP materials with long luminous life and high photoluminescence quantum yield (PLQY). Herein, two organic molecules, 1,4‐phenylenebisboronic acid (PBA) with high PLQY and isophthalic acid (IPA) with long lifetime, are orderly combined into two crystalline hydrogen‐bonded organic chains, named as PBA‐IPA1 and PBA‐IPA2, through supramolecular self‐assembly. Compared with PBA‐IPA1, PBA‐IPA2 shows much improved phosphorescent lifetime (1.59 s) and PLQY (15.72%) due to the triplet–triplet energy transfer between two components, which is further confirmed by computational studies. The obtained material can be potentially used in such areas as information encryption and fingerprint identification, providing a new strategy for design of UOP materials for practical applications. [ABSTRACT FROM AUTHOR]

On account of the scarcity of molecules with a satisfactory second near-infrared (NIR-II) response, the design of high-performance organic NIR photothermal materials has been limited. Herein, we investigate a cocrystal incorporating tetrathiafulvalene (TTF) and tetrachloroperylene dianhydride (TCPDA) components. A stable radical was generated through charge transfer from TTF to TCPDA, which exhibits strong and wide-ranging NIR-II absorption. The metal-free TTF-TCPDA cocrystal in this research shows high photothermal conversion capability under 1064 nm laser irradiation and clear photothermal imaging. The remarkable conversion ability-which is a result of twisted components in the cocrystal-has been demonstrated by analyses of single crystal X-ray diffraction, photoluminescence and femtosecond transient absorption spectroscopy as well as theoretical calculations. We have discovered that space charge separation and the ordered lattice in the TTF-TCPDA cocrystal suppress the radiative decay, while simultaneously strong intermolecular charge transfer enhances the non-radiative decay. The twisted TCPDA component induces rapid charge recombination, while the distorted configuration in TTF-TCPDA favors an internal non-radiative pathway. This research has provided a comprehensive understanding of the photothermal conversion mechanism and opened a new way for the design of advanced organic NIR-II photothermal materials., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)