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 mechanofluorochromism phenomena were excellent. The powder XRD results confirmed that the morphology conversion between crystalline and amorphous phases was responsible for the mechanofluorochromic characteristics of 1–4. This work provides valuable reference for the exploitation of high-contrast mechanochromism materials.