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Thermofluorochromic materials exhibit tunable fluorescence emission on heating or cooling. They are highly desirable for applications ranging from temperature sensing to high-security anti-counterfeiting. Luminescent matrices based on liquid crystals are very promising, particularly those based on liquid crystals with intrinsic fluorescence. However, only a few examples have been reported, suggesting ample margins for development in the field, due to the wide range of fluorophores and supramolecular organizations to be explored. Moreover, thermofluorochromic liquid crystals can be tailored with further functionalities to afford multi-stimuli responsive materials. For the first time, herein we report the thermofluorochromism of thienoviologen liquid crystals, already known to show bulk electrochromism and electrofluorochromism. In particular, we studied their photophysics in the 25 °C–220 °C range and as a function of the length of the N-linear alkyl chains, m (9 ≤ m ≤ 12 C atoms), and the type of anion, X (X = OTs-, OTf-, BF4-, NTf2-). Interestingly, by changing the parameters m, X and T, their fluorescence can be finely tuned in the whole visible spectral range up to the NIR, by switching among different mesophases. Importantly, by fixing the structural parameters m and X, an interesting thermofluorochromism can be achieved for each thienoviologen in a homologous series, leading to a switch of the emitted light from red to green and from white to blue as a consequence of the temperature-induced variation in the supramolecular interactions in the self-assembled phases.

Fluorescent light modulation by small electric potentials has gained huge interest in the past few years. This phenomenon, called electrofluorochromism, is of the utmost importance for applications in optoelectronic devices. Huge efforts are being addressed to developing electrofluorochromic systems with improved performances. One of the most critical issue is their low cyclability, which hampers their widespread use. It mostly depends on the intrinsic reversibility of the electroactive/fluorophore molecular system and on device architecture. Here we show a novel fluorene-based mixed-valence electrofluorochromic system that allows direct electrofluorochromic switching and exhibits incomparable electrochemical reversibility and device cyclability of more than 10 000 cycles.