Carbazole-based highly solid-state emissive fluorene derivatives with various mechanochromic fluorescence characteristics

Four carbazole-based fluorene derivatives 1-4 have been successfully prepared. All these compounds showed highly solid-state emissive feature with various fluorescence. The aggregation-induced emission effect of compound 1 was investigated by the systematic research of photoluminescence spectroscopy, and the results indicated that luminogen 1 displayed obvious aggregation-induced yellow light-emitting phenomenon. In addition, the solid-state emission behaviors of these fluorescent molecules could be tuned by mechanical force. More specifically, luminogens 1 and 2 showed reversible mechanochromic fluorescence conversion between blue-green and yellowish brown emission colors, luminogens 3 and 4 exhibited reversible mechanochromic fluorescence conversion involving color changes from green or yellow to yellowish brown. Furthermore, the repeatabilities of their mechano-fluorochromism phenomena were excellent. The powder XRD results confirmed that the morphology conversion between crystalline and amorphous phases was responsible for the mechano-fluorochromic characteristics of 1-4. This work provides valuable reference for the exploitation of high-contrast mechanochromism materials.