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Single‐molecule localization microscopy (SMLM) has found extensive applications in various fields of biology and chemistry. As a vital component of SMLM, fluorophores play an essential role in obtaining super‐resolution fluorescence images. Recent research on spontaneously blinking fluorophores has greatly simplified the experimental setups and extended the imaging duration of SMLM. To support this crucial development, this review provides a comprehensive overview of the development of spontaneously blinking rhodamines from 2014 to 2023, as well as the key mechanistic aspects of intramolecular spirocyclization reactions. We hope that by offering insightful design guidelines, this review will contribute to accelerating the advancement of super‐resolution imaging technologies. [ABSTRACT FROM AUTHOR]

Single‐molecule localization microscopy (SMLM) has found extensive applications in various fields of biology and chemistry. As a vital component of SMLM, fluorophores play an essential role in obtaining super‐resolution fluorescence images. Recent research on spontaneously blinking fluorophores has greatly simplified the experimental setups and extended the imaging duration of SMLM. To support this crucial development, this review provides a comprehensive overview of the development of spontaneously blinking rhodamines from 2014 to 2023, as well as the key mechanistic aspects of intramolecular spirocyclization reactions. We hope that by offering insightful design guidelines, this review will contribute to accelerating the advancement of super‐resolution imaging technologies. [ABSTRACT FROM AUTHOR]

The twisted intramolecular charge transfer (TICT) mechanism has guided the development of numerous bright and sensitive fluorophores. This review briefly overviews the history of establishing the TICT mechanism, and systematically summarizes the molecular design strategies in modulating the TICT tendency of various organic fluorophores towards different applications, along with key milestone studies and representative examples. Additionally, we also succinctly review the twisted intramolecular charge shuttle (TICS) and twists during photoinduced electron transfer (PET), and compare their similarities and differences with TICT, with emphasis on understanding the structure–property relationships between the twisted geometries and how they can directly affect the fluorescence of the molecules. Such structure–property relationships presented herein will greatly aid the rational development of fluorophores that involve molecular twisting in the excited state. [ABSTRACT FROM AUTHOR]

Fluorescent thermometers based on organic dyes play an important role in the visualization of dynamic temperature topography with high resolution. Many molecular thermometers contain two fluorophores with different temperature responses to achieve ratiometric temperature detection. However, the stability and reliability of such ratiometric thermometers are highly dependent on the susceptibility of the fluorophores towards photobleaching. Despite the use of single-fluorophore ratiometric thermometers in previous reports, the difficulty and complexity in their molecular design and synthesis severely hinder their widespread applicability. In this work, we have investigated the use of commercially available dyes (i.e., BD140 and LD688) with conformational isomers as ratiometric thermometers. Each of these dyes consists of a mixture of conformers with distinct UV-vis absorption and emission spectra. The thermal equilibrium of these conformers successfully enabled the development of ratiometric thermometers with good stability and reliability. [ABSTRACT FROM AUTHOR]

Abstract: Hydrogen sulfide has emerged as an important biological messenger and much attention has been paid to the design of fluorescent probes for H2S to meet the requirement of accurate measurement of H2S. In this work, a new red emission fluorescent probe for H2S was developed based on the reduction reaction of azide with H2S to amine with the fluorophore of dicyanomethylenedihydrofuran because of its long excitation and emission wavelength. The probe has a high selectivity for H2S over competitive anions and sulfide-containing analytes. Finally, the probe was applied to sense H2S in living cells. [Copyright &y& Elsevier]

Inhibition of TICT can significantly increase the brightness of fluorescent materials. Accurate prediction of TICT is thus critical for the quantitative design of high‐performance fluorophores and AIEgens. TICT of 14 types of popular organic fluorophores were modeled with time‐dependent density functional theory (TD‐DFT). A reliable and generalizable computational approach for modeling TICT formations was established. To demonstrate the prediction power of our approach, we quantitatively designed a boron dipyrromethene (BODIPY)‐based AIEgen which exhibits (almost) barrierless TICT rotations in monomers. Subsequent experiments validated our molecular design and showed that the aggregation of this compound turns on bright emissions with ca. 27‐fold fluorescence enhancement, as TICT formation is inhibited in molecular aggregates. [ABSTRACT FROM AUTHOR]

Inhibition of TICT can significantly increase the brightness of fluorescent materials. Accurate prediction of TICT is thus critical for the quantitative design of high‐performance fluorophores and AIEgens. TICT of 14 types of popular organic fluorophores were modeled with time‐dependent density functional theory (TD‐DFT). A reliable and generalizable computational approach for modeling TICT formations was established. To demonstrate the prediction power of our approach, we quantitatively designed a boron dipyrromethene (BODIPY)‐based AIEgen which exhibits (almost) barrierless TICT rotations in monomers. Subsequent experiments validated our molecular design and showed that the aggregation of this compound turns on bright emissions with ca. 27‐fold fluorescence enhancement, as TICT formation is inhibited in molecular aggregates. [ABSTRACT FROM AUTHOR]

Charge transfer and separation are important processes governing numerous chemical reactions. Fundamental understanding of these processes and the underlying mechanisms is critical for photochemistry. Herein, we report the discovery of a new charge‐transfer and separation process, namely the twisted intramolecular charge shuttle (TICS). In TICS systems, the donor and acceptor moieties dynamically switch roles in the excited state because of an approximately 90° intramolecular rotation. TICS systems thus exhibit charge shuttling. TICSs exist in several chemical families of fluorophores (such as coumarin, BODIPY, and oxygen/carbon/silicon–rhodamine), and could be utilized to construct functional fluorescent probes (i.e. viscosity‐ or biomolecule‐sensing probes). The discovery of the TICS process expands the current perspectives of charge‐transfer processes and will inspire future applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Spirolactam based pH probes (RLH A-C) were built with Rhodamine 6G, Rhodamine B and Rhodamine 101 to discuss the tuning effect of rhodamine fluorophore. • The p K a values and observed rate constant k obs of RLH A-C were determined and found to negatively correlated with the calculated Gibbs free energy differences ΔG C-O and ΔG TS respectively. • The p K a values and observed rate constant k obs of RLH A-C determined the potential application in intracellular pH detection. Ring-opening reaction of rhodamine spirolactam has been widely applied to construct fluorescent probes. The fluorescence properties of the probe were finely tuned for specific purpose through changing the rhodamine fluorophore. However, the influence on response range and kinetic parameters of the probe during the change has been seldom discussed. Herein, we took pH detection as an example and constructed spirolactam based probes (RLH A-C) with Rhodamine 6G, Rhodamine B and Rhodamine 101. The p K a values and observed rate constant k obs of RLH A-C were determined and found to negatively correlated with the calculated Gibbs free energy differences ΔG C-O and ΔG TS respectively. The potential applications of RLH A-C in imaging acidic microenvironment were also investigated in cells. We expect the comparison of rhodamine fluorophores will facilitate the quantitative optimization of rhodamine spirolactam based fluorescent probes. [ABSTRACT FROM AUTHOR]

Abstract: Fluorescent probes for hydrogen sulfide have received considerable attention because of the biological significance of H2S recognized recently. However, near-infrared fluorescent probes for H2S are still rare. In this work, a new near-infrared fluorescent probe for H2S was developed based on the reduction reaction of azide with H2S to amine based on the fluorophore of dicyanomethylene-4H-chromene because of its long excitation and emission wavelength. The probe has a high selectivity for H2S over competitive anions and sulfide-containing analytes. Finally, the probe was applied to sense H2S in living cells. [Copyright &y& Elsevier]