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In the realm of biological research, the invention of super-resolution microscopy (SRM) has enabled the visualization of ultrafine sub-cellular structures and their functions in live cells at the nano-scale level, beyond the diffraction limit, which has opened up a new window for advanced biomedical studies to unravel the complex unknown details of physiological disorders at the sub-cellular level with unprecedented resolution and clarity. However, most of the SRM techniques are highly reliant on the personalized special photophysical features of the fluorophores. In recent times, there has been an unprecedented surge in the development of robust new fluorophore systems with personalized features for various super-resolution imaging techniques. To date, xanthene, cyanine, oxazine and BODIPY cores have been authoritatively utilized as the basic fluorophore units in most of the small-molecule-based organic fluorescent probe designing strategies for SRM owing to their excellent photophysical characteristics and easy synthetic acquiescence. Since the future of next-generation SRM studies will be decided by the availability of advanced fluorescent probes and these four fluorescent building blocks will play an important role in progressive new fluorophore design, there is an urgent need to review the recent advancements in designing fluorophores for different SRM methods based on these fluorescent dye cores. This review article not only includes a comprehensive discussion about the recent developments in designing fluorescent probes for various SRM techniques based on these four important fluorophore building blocks with special emphasis on their effective integration into live cell super-resolution bio-imaging applications but also critically evaluates the background of each of the fluorescent dye cores to highlight their merits and demerits towards developing newer fluorescent probes for SRM. [ABSTRACT FROM AUTHOR]

A new water soluble and fluorogenic probe (L) that can demonstrate a specific ratiometric detection of a SO2 derivative (SO32−) in 100% aqueous medium and live cells has been designed and synthesized. The detection process can be visualized by the naked eye, as the orange-red fluorescence of L turns into a strong blue fluorescence upon interaction with SO32−. L displayed several beneficial attributes such as detection in complete aqueous medium, extremely fast response time along with high selectivity and sensitivity. The ratiometric sensing was attributed to the selective nucleophilic addition reaction of SO32− with L. The probe was further used to develop a low cost microfluidic sensor device (μPAD). The probe was biocompatible and its potential to sense SO32− in mitochondria was captured in live HeLa cells. [ABSTRACT FROM AUTHOR]

A meta-phenylenediamine-based disubstituted bis-urea receptor L1 with electron-withdrawing 3-chloro and electron-donating 4-methylphenyl terminals has been established as a potential system to fix and efficiently capture atmospheric CO2 as air-stable entrapment of an unprecedented {CO32−–(H2O)2–CO32−} cluster (complex 1a) within its tetrameric long straight pillar-like assembly entirely sealed by n-TBA cations via formation of a barrel-type architecture. L1 and its isomeric 4-bromo-3-methyl disubstituted bis-urea receptor L2 have been found to entrap similar kinds of water-free naked sulfate–sulfate double anion (complexes 1b and 2a) by cooperative binding of urea moieties inside the two pairs of the inversion-symmetric linear tetrameric barrel of L1 and L2, respectively. On the other hand, in the presence of excess halides, L1 self-assembles to form hexa-coordinated fluoride complex 1c and tetra-coordinated bromide complex 1d, while L2 self-assembles to form penta-coordinated fluoride complex 2b in the solid state via semicircular receptor architectures and non-cooperative H-bonding interactions of urea moieties. [ABSTRACT FROM AUTHOR]

A simple organic molecule (L3) has been systematically designed and developed to generate white-light emission from a single-component system. It could also tune several emission colors owing to its diverse spectral nature with varying water fractions in methanol–water and acetonitrile–water mixtures. Essentially, the introduction of an aggregation-induced emission (AIE) phenomenon and excimer-forming ability in the molecular system provided the scope for a dual emission, whereas ESIPT (excited state intramolecular proton transfer) coupled-AIE phenomenon acted as an additional means of adjusting the emission wavelength of the corresponding emission peak by varying the solvent polarity. Detailed AFM (atomic force microscopy), DLS (dynamic light scattering) and X-ray crystallographic studies were carried out to validate the mechanism of generation of white-light emission. [ABSTRACT FROM AUTHOR]

A judiciously designed fluorogenic probe (L) rendered rapid and differential turn-on responses by exhibiting strong blue fluorescence (λem = 442 nm) for SO32− and greenish-yellow fluorescence (λem = 511 nm) for SO42−/HSO4− in 100% aqueous medium and live cells. [ABSTRACT FROM AUTHOR]

A versatile new fluorogenic Schiff base probe (L) has been synthesized by the reaction of quinoline-2-carbohydrazide (which acts as the chelating site) and 4-dimethylamino cinnamaldehyde (which acts as the signaling unit). L can sense three of the most biologically and environmentally important metal ions, Zn2+, Cd2+ and Pb2+, among various tested metal ions through selective TURN-ON fluorescence responses in physiological pH. Interestingly, L can not only sense Zn2+, Cd2+ and Pb2+ fluorometrically in physiological conditions but can also distinguish one from another by exhibiting individual intrinsic left-right-center TURN-ON emission signal swings. These selective fluorescence responses were explained by a chelation-enhanced fluorescence (CHEF) mechanism. Theoretical calculations were carried out to ascertain the preferred L–metal ion binding mode. [ABSTRACT FROM AUTHOR]