Mechanofluorochromic property of coumarin derivatives containing carbonyl group

Four novel coumarin derivatives with different substituents (CMCO-H, CMCO-F, CMCO-CH3 and CMCO-CF3) functionalized by carbonyl unit were designed and synthesized. The relationship between spatial structure and photophysical properties of these coumarin compounds in different states had been systematically studied. In the single molecule state, with the increase of solvent polarities, the fluorescent peaks exhibited obvious solvatochromic effect, accompanied by a decrease in intensity. The significant solvatochromism effect suggested that these four coumarin derivatives both are typical intramolecular charge transfer molecules. The density functional theory calculation results showed that the electron clouds were transferred from coumarin unit and the connected aromatic ring to carbonyl and styrenyl groups. Meanwhile, compounds CMCO-CH3 and CMCOCF3 exhibited reversible mechanofluorochromic (MFC) property between yellow and orange emission. The single crystal XRD, powder XRD and SEM experiment suggested that the modulation of photophysical properties come from the change of compounds spatial structures. The study provided an efficient way for the design of organic compounds with MFC property.