A Smart Molecule Showing Spin Crossover Responsive Aggregation-Induced Emission

The utilization of spin crossover(SCO)to modulate the luminescence properties in smart multifunctional materials and multichannel sensors is promising.However,it is challenging to build a strong coupling between SCO and luminescence in one system.Herein,we present a mononuclear compound[Fe(tpe-abpt)_(2)(SeCN)_(2)]·4DMF(1·4DMF,tpe-abpt:(4-(1,1,2,2-tetraphenylethene))-N-(3,5-bis(pyridin-2-yl)-4H-1,2,4-triazol-4yl)methanimine)showing aggregation-induced emission(AIE)and thermally induced SCO properties.Variable-temperature single-crystal structural analysis reveals that SCO changes the number of pathways and strength of intermolecular interactions,resulting in deactivation of nonradiative decay and significant enhancement of luminescence.The photoluminescence(PL)intensity of 1·4DMF exhibited a fivefold increase upon the spin transition from the low-spin to the high-spin states.In contrast with the current strategy of controlling the Förster resonance energy transfer(FRET)process by utilizing SCO to tune the overlap degree between the emission band of the luminophore and UV–vis absorption band of high-spin and low-spin states,we developed a new approach to tune the intermolecular interactions between AIE luminogens(AIEgens)by utilizing a subtle SCO-induced structural transformation,therefore leading to effective coupling between SCO and luminescence and a significant change in luminescence upon SCO.Our results provide a rational strategy to build smartmultifunctionalizedmaterials with remarkably synergetic SCO and luminescence.