Stable Multiresponsive Luminescent MOF for Colorimetric Detection of Small Molecules in Selective and Reversible Manner

A novel Cu­(I)-based two-dimensional (2D, 4⁴ net) metal–organic framework (MOF) [Cu­(L)­(I)]_2<i>n</i>·2<i>n</i>DMF·<i>n</i>MeCN (<b>1</b>); L = 4′-(4-methoxyphenyl)-4,2′:6′,4″-terpyridine; DMF = <i>N</i>,<i>N</i>-dimethylformamide, MeCN = acetonitrile) has been synthesized and found to behave as a colorimetric detector for the widest variety of small molecules such as different solvents, halobenzenes, N-heterocycles, amine, and nitroaromatic explosives all in vapor phase through a single crystal to single crystal (SCSC) transformation. The 2D 4⁴ nets are interdigitated with each other to form a supramolecular 3D MOF having 1D pore. The interdigitated layers are stabilized by π···π interactions and CH···π interactions and provide extreme stability up to 380 °C. Interestingly, all guest exchange and encapsulation processes are reversible without loss of structural integrity. Positions of the guest molecules in the host–guest complex have been identified from the crystal structure and found to involve weak interactions with the framework. Notably, this is the first time for a report of any material which encapsulates such a large number of small molecules in the vapor phase from different chemical classes in SCSC fashion with visible color changes. Tests confirm the selectivity toward most polar molecule in a class. In the presence of guest molecules, the MOF exhibits a blue shift in fluorescence emission spectra and the extent of the blue shift is appreciably high. It also shows high selectivity toward diethylamine (dea) among N-heterocycles, amine, and highly explosive trinitrophenol (TNP) among nitroaromatic explosives as revealed from concurrent luminescence quenching in solution. Finally, the MOF represents one of the best hosts reported so far having extreme stability and selectivity and meets the benchmark of reversibility for material applications