Compounds exhibiting tuneable fluorescence emission upon heating or cooling are considered smart materials as their optical properties can be exquisitely controlled by adjusting the external temperature. Herein, we report such a material, which is a porous pyrene-based metal–organic framework with a chemical formula of [Mg1.5(HTBAPy)(H2O)2]·3DMF (H4TBAPy = 1,3,6,8-tetrakis(p-benzoic acid)pyrene), named >SION-7. The bulk solid material of >SION-7 can display either monomer or excimer fluorescence emission due to the temperature-dependent extent of interchromophoric interactions between the HTBAPy3– ligands within the framework. Consequently, the fluorescence emission colours gradually change from blue at low temperature (80 K) to yellow-green at high temperature (450 K). Interestingly, while kept in a relatively wide temperature range of 80–200 K, >SION-7 displays a structured monomer-like spectrum and its colour changes reversibly from deep to light blue. Ex situ variable-temperature (100–350 K) single-crystal X-ray diffractometry studies revealed the impact of solvent content on the optical properties of >SION-7, and illustrated the correlation between the position of the phenylene groups of the HTBAPy3– ligands at different temperatures and the interchromophoric interaction. Our study demonstrates a step forward towards the design of tuneable thermofluorochromic materials sought by optoelectronics.
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