Achieving Organic Smart Fluorophores by Controlling the Balance between Intermolecular Interactions and External Stimuli

Full-Color "Off-On" Thermochromic Fluorescent Fibers for Customizable Smart Wearable Displays in Personal Health Monitoring

Responsive thermochromic fiber materials capable of miniaturization and integrating comfortably and compliantly onto the soft and dynamically deforming human body are promising materials for visualized personal health monitoring. However, their development is hindered by monotonous colors, low-contrast color changes, and poor reversibility. Herein, full-color "off-on" thermochromic fluorescent fibers are prepared based on self-crystallinity phase change and Förster resonance energy transfer for long-term and passive body-temperature monitoring, especially for various personalized customization purposes. The off-on switching luminescence characteristic is derived from the reversible conversion of the dispersion state and fluorescent emission by fluorophores and quencher molecules, which are embedded in the matrix of a phase-change material, during the crystallizing/melting processes. The achievement of full-color fluorescence is attributed to the large modulation range of fluorescence colors according to primary color additive theory. These thermochromic fluorescent fibers exhibit good mechanical properties, fluorescent emission contrast, and reversibility, showing their great potential in flexible smart display devices. Moreover, the response temperature of the thermochromic fibers is controllable by adjusting the phase-change material, enabling body-temperature-triggered luminescence; this property highlights their potential for human body-temperature monitoring and personalized customization. This work presents a new strategy for designing and exploring flexible sensors with higher comprehensive performances.

Multi-action of a Fluorophore in the Sight of Light: Release of NO, Emergence of FONs, and Organelle Switching

Light, as an external stimulus, has begun to engage a phenomenal role in the diverse field of science. Encouraged by recent progress from biology to materials chemistry, various light-responsive fluorescent probes have been developed. Herein, we present a 1,8-naphthalimide-based probe NIT-NO₂ capable of releasing nitric oxide (NO) along with the formation of fluorescent organic nanoparticles (FONs) upon exposure to near-visible UV light. By synthesizing the photoproduct NIT-OH, we unveiled that initially NIT-NO₂ released NO and converted to NIT-OH, while prolonged irradiation led to the formation of FONs that is corroborated by the red-edge excitation shift as well as microscopic investigation. Finally, we have successfully applied NIT-NO₂ and NIT-OH for specific labeling of lipid droplets and plasma membranes, respectively, and demonstrated the switching from lipid droplets to plasma membranes by using light as a stimulus. These two probes show unique imaging applications inside the cells depending on the polarity and hydrophobicity of the environment. This work paves a fascinating way for the generation of excitation-dependent FONs from a small organic fluorophore and highlights its potency as an exclusive imaging tool.

The Rainbow Arching over the Fluorescent Thienoviologen Mesophases

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.

Two-Fold Intramolecular Phosphacyclization: From Fluorescent Diphosphapyrene Salts to Pentavalent Derivatives

The synthesis of π-extended pyrene-based luminescent compounds containing two six-membered phosphacycles has been realized through a two-step synthesis. It involves a Cu(II)-mediated double cyclization of tertiary diphosphane derivatives to afford dicationic molecules with quaternized phosphorus centers. Subsequent transformation of diphosphonium species into the corresponding P-oxide derivatives has been successfully achieved through Pd(0)-assisted cleavage of the P-Ph bonds, which opens a promising way for the functionalization of polyaromatic P-systems.