Combined Experimental and Theoretical Studies on the Rubbing-Induced Fluorescence Behavior of a Luminophore in the Solid State.

It is intricate to break and make chemical bonds in solid states compared to their solution states, so it is imperative to ascertain green proficient approaches by regulating the solid-state structures and their related material properties. Here, the rubbing-induced photoluminescence behavior of a luminophore (RIL) of the benzimidazole family in the solid state has been accomplished. Interestingly, upon gentle rubbing or mere scratching, solid-state fluorescence from the nonemissive pristine RIL was observed due to the aggregation-induced emission (AIE) phenomenon in the solid state, for which the phenolic moiety is present in the molecule and is accountable. The structure-property relationship of RIL and the mechanism responsible for this solid-state fluorescence characteristics have been explained with the help of experimental (using the single-crystal structure, powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) images, etc.) and theoretical (by DFT and TDDFT) studies. The crystal arrangements with different stacking interactions and the SEM images after being rubbed revealed that the mechanical force- or pressure-induced slight deformation in the crystal arrangement notably facilitated the strong emission in the solid state. This rubbing-induced solid-state fluorescence in a new luminophore (RIL) through stacking of layers restricting the molecular motion has been developed here for the first time, and it can be explicitly employed in steganography techniques for data security. This present study will open up a new insight into the use of this RIL as a solid-state smart material for data security in coding devices in the future, and this developed approach may be helpful to ameliorate the design of new-generation smart materials by modifying the structure to attain other characteristics.

A new metal-free benzorhodol-based photoluminophore selective for carbon monoxide detection applicable in both in vitro and in vivo bioimaging.

A new benzorhodol-based non-fluorescent organic frame (DEB-CO) detects carbon monoxide (CO) selectively through a spirolactam ring-opening mechanism. Herein, the selective off-on fluorogenic behavior of this probe towards CO has been achieved without any assistance of precious and hazardous metals (e.g. Pd2+) as additional substrates. Moreover, the red-emissive probe motivated us to apply in situ tracing in mice and living cells. The selective off-on fluorogenic behavior of this probe towards CO originating from CORM-3 in vitro and in vivo with a limit of detection as low as 64.29 nM (for CORM-3) has been observed. Additionally, this probe is capable of sensing toxic carbon monoxide gas. This probe has also been utilized to detect intracellular CO in MCF7 cells (in vitro) and to spot the distribution of CO in mice (in vivo) by acquiring bioimages with the help of confocal microscopy, which indicates that DEB-CO is a smart competent probe for this purpose.

A deoxygenation-switch-based red-emitting fluorogenic light-up probe for the detection of highly toxic free bilirubin in human blood serum.

Reaction-based chemical switches are attracting great interest due to their high selectivity, and their use has become a powerful technique for developing fluorogenic probes. Herein, a benzorhodol-derivative-attached N-oxide probe (DEBNox) has been designed as a new fluorogenic probe for the detection of the biologically toxic species bilirubin based on a deoxygenation switching mechanism. Upon reaction with added Fe3+, bilirubin produces Fe2+ ions in situ, which in turn promote a deoxygenation reaction with DEBNox to generate the corresponding high-red-fluorescence (λem: ∼623 nm) benzorhodol derivative (DEB). This type of Fe3+-mediated response helps the probe to act as a qualified turn on selective fluorescence sensor for bilirubin with a detection range as low as 33 nM. Moreover, the probe was successfully employed to detect free bilirubin in human blood serum specimens with acceptable accuracy and reliability. This DEBNox-based light-up strategy also facilitates the construction of reliable and highly sensitive assays based on a paper-based strategy, similar to pH-indicator paper, as is demonstrated here via bilirubin detection in real serum samples. These findings could be useful for developing powerful diagnostic tools for the detection of free bilirubin in the near further.

A Nuclear-Localized Naphthalimide-Based Fluorescent Light-Up Probe for Selective Detection of Carbon Monoxide in Living Cells.

A nuclear-localized fluorescent light-up probe, NucFP-NO2, was designed and synthesized that can detect CO selectively in an aqueous buffer (pH 7.4, 37 °C) through the CO-mediated transformation of the nitro group into an amino-functionalized moiety. This probe triggered a more than 55-fold "turn-on" fluorescence response to CO without using any metal ions, e.g., Pd, Rh, Fe, etc. The enhanced response is highly selective over a variety of relevant reactive oxygen, nitrogen, and sulfur species and also various biologically important cationic, anionic, and neutral species. The detection limit of this probe for CO is as low as 0.18 µM with a linear range of 0-70 µM. Also, this fluorogenic probe is an efficient candidate for monitoring intracellular CO in living cells (RAW 264.7, A549 cells), and the fluorescence signals predominantly localize in the nuclear region.

Bilirubin Quantification in Human Blood Serum by Deoxygenation Reaction Switch-Triggered Fluorescent Probe.

A coumarin-based fluorescent compound, bilirubin fluorescent probe N-oxide (BFPNox), was successfully designed and synthesized for highly selective and sensitive detection of free bilirubin with short response time. The fluorescence "turn-on" response of the probe is based on the in situ generated Fe2+-mediated deoxygenation reaction of N-oxide from the diethylarylamine group of the probe, where the group attached to the coumarin π-conjugated system is responsible for the fluorescence quenching state of the probe, BFPNox. Here, the reaction of the added Fe3+ ions with bilirubin produces Fe2+ ions in situ in aqueous buffer. Fluorescence enhancement of BFPNox was achieved by more than 12-fold when a double equivalent of bilirubin solution was added in reaction buffer at pH 7.2 (50 mM HEPES, 5% DMSO) at 25 °C under excitation at 400 nm. It detected free bilirubin as low as 76 nM in an aqueous system without any interference of metal ions, anions, and other important biomolecules with a linear concentration range of 0-10 µM (R2 = 0.991). The probe was also employed in the estimation of free bilirubin in human serum specimens to verify the efficacy of this probe. With these, it is revealed that this probe is a good candidate to be used as a powerful diagnostic tool for the assessment of free bilirubin with significant accuracy and reliability.

A Lysosome-Targetable Fluorescence Sensor for Ultrasensitive Detection of Hg2+ in Living Cells and Real Samples.

A new lysosome-targetable fluorescence sensor, Lyso-HGP, was designed and synthesized based on 4-methyl-2,6-diformylphenol as a fluorophore. Lyso-HGP displays highly sensitive fluorescent detection of Hg2+ in HEPES buffer solution (10 mM, DMSO 1%) of pH 7.0 at 37 °C due to the formation of highly fluorescent formyl-functionalized derivative Lyso-HGP-CHO. The sensor triggered a "turn-on" fluorescence response to Hg2+ with a simultaneous increase of fluorescence intensity by 180-fold just after 10 min. The response is very selective over a variety of biologically relevant cations, anions, molecules, and competitive toxic heavy metal cations. The limit of detection (LOD) was calculated as low as 6.82 nM. So, it can be utilized to detect this toxic heavy metal in biology and environmental samples in an aqueous buffer medium. Also, the sensor is able to monitor the subcellular distribution of Hg2+ specifically localized in the lysosome's compartment in the MCF7 human breast cancer cell line by fluorescence microscopy.