Wide-Color-Span: Blue-Shifted Thermochromic D-A-D Fluorophores for Ratiometric Temperature Sensing

Thermochromic fluorescent materials have significant application prospects in the field of temperature sensing. In this study, based on the donor–acceptor–donor (D-A-D) strategy, two fluorescent molecules, MPT-1 and MPT-2, with fluorenyl cores and methoxy phenothiazine as donors, were synthesized via the Buchwald–Hartwig C–N cross-coupling reaction, and their structures were confirmed by 1H NMR, 13C NMR and HRMS. Thermogravimetric analysis indicated that both compounds exhibited excellent thermal stability (Td = 377 °C, 413 °C). Aggregation-induced emission (AIE) experiments showed that the emission peak blue-shifted by approximately 42–44 nm with increasing aggregation. Temperature-dependent fluorescence studies indicated that from 80 K to 300 K, the emission peaks of both molecules shifted continuously from the yellow region to the blue region. The relative sensitivities of MPT-1 and MPT-2 were 2.5% K−1 and 2.19% K−1, respectively, with CIE ΔE shifts of 0.19 and 0.18. This study elucidates the thermochromic mechanism of D-A-D-type fluorescent molecules, confirms the tunability of their emission colour in response to temperature, and provides theoretical guidance and experimental reference for the design of novel thermochromic fluorescent materials and their applications in temperature sensing.