Organic near-infrared room temperature phosphorescence materials have unparalleled advantages in bioimaging due to their excellent penetrability. However, limited by the energy gap law, the near-infrared phosphorescence materials (>650 nm) are very rare, moreover, the phosphorescence lifetimes of these materials are very short. In this work, we have obtained organic room temperature phosphorescence materials with long wavelengths (600/657–681/732 nm) and long lifetimes (102–324 ms) for the first time through the guest-host doped strategy. The guest molecule has sufficient conjugation to reduce the lowest triplet energy level and the host assists the guest in exciton transfer and inhibits the non-radiative transition of guest excitons. These materials exhibit good tissue penetration in bioimaging. Thanks to the characteristic of long lifetime and long wavelength emissive phosphorescence materials, the tumor imaging in living mice with a signal to background ratio value as high as 43 is successfully realized. This work provides a practical solution for the construction of organic phosphorescence materials with both long wavelengths and long lifetimes.

Three novel D–A-type pyranone–carbazole compounds were found to exhibit crystal-induced room temperature phosphorescence and reversible photochromic activities through strong intermolecular interactions.

No abstract

The adjustment of the luminescent properties of materials according to different environments has always been a hot topic. Among them, the local excited (LE) state and the twisted intramolecular charge-transfer (TICT) state are important factors that affect the photophysical properties of compounds. Herein, four donor–acceptor pyranone–arylbenzene molecules were synthesized using pyranone (Pr) as the acceptor and phenyl (Ph), naphthalene (Np), anthracene (An), and pyrene (Py) as donors, respectively. The results of experiments and theoretical calculations show that the TICT state dominates the luminescent properties of Pr–Ph and Pr–Np, which results in fluorescence quenching in solution and solid states. However, Pr–An and Pr–Py are dominated by the LE state caused by rigid anthracene and pyrene, and the twisted molecular conformations avoid the strong π–π interactions, leading to dual-state emissions. Moreover, Pr–An has two completely different polymorphs, Pr–An-SB and Pr–An-YG, which emit sky-blue and yellow-green fluorescence due to different conformations and stacking arrangements, respectively. Both the polymorphs can be transformed into an amorphous state that emits dark cyan fluorescence upon grinding, revealing high-contrast mechanofluorochromic properties. Furthermore, Pr–An-YG can be converted into more stable Pr–An-SB by solvent fumigation, revealing vapochromic activity. This work provides some useful information for the development of fluorescent materials based on LE and TICT states.

No abstract