An AIE molecule featuring changeable triplet emission between phosphorescence and delayed fluorescence by an external force

Abstract

In this article, we report a newly designed molecule ODFRPTZ with an asymmetric D–A–D′ type structure. ODFRPTZ is endowed with aggregation-induced emission (AIE), intriguing mechanochromism and changeable emission between delayed fluorescence and phosphorescence. In the THF/H₂O system, the emission efficiency of ODFRPTZ is greatly improved by increasing the water fraction due to the restriction of the intramolecular rotation and vibration in the aggregation states. Intriguingly, ODFRPTZ shows mechanochromic properties under both UV light and visible light. The emission color switches from green to yellow and the color under visible light changes from white to yellow after grinding due to the changeable conformations of phenothiazine from quasi-axial to quasi-equatorial. The crystalline powder shows prompt fluorescence and phosphorescence characteristics. The lifetime of phosphorescence continuously increases from 0.4 ms at 300 K to 121.1 ms at 77 K. The emission of ground powder is composed of prompt fluorescence and delayed fluorescence with lifetimes of 18.7 ns and 0.9 μs, respectively. To the best of our knowledge, it is a rarely reported AIE example that the triplet state emission can be altered from phosphorescence to delayed fluorescence by an external force.