Y-shaped fluorophore: Synthesis, crystal structure and picric acid detection

Tryptanthrin incorporated spiropiperidine derivative as a fluorescent chemosensor for picric acid detection

The photophysical properties of a previously synthesized tryptanthrin incorporated spiropiperidine molecule (CTSP) is described. Studies revealed that the fluorescence of the compound gets significantly quenched by addition of picric acid (PA). The selectivity, anti-interference and quenching mechanistic studies are also described. The quenching mechanism was largely attributed to photo-induced electron transfer (PET) process facilitated by a strong electrostatic interaction between the protonated NH2 group of CTSP and PA. Additionally, pH variations significantly influenced the quenching efficiency, with the highest response observed at neutral pH. These findings demonstrate that CTSP is a promising candidate for PA detection, with potential applications in environmental monitoring and security fields.

Advances in Organic Synthesis and Properties Based On Tetraphenylimidazole Derivatives

1,2,4,5-Tetraphenylimidazole derivatives exhibit unique conjugated structures, photophysical properties, and multifunctional properties by virtue of the phenyl functional groups introduced at specific positions of the imidazole ring. However, there is still a lack of systematic research on them, which limits their further development and application. In this paper, we comprehensively review the research progress in the fields of organic synthesis, mechanistic fluorescence color change, chemiluminescence, OLED and fluorescent sensors, especially focusing on the hotspot of fluorescent sensors. Finally, it summarizes the challenges in the current research and looks forward to the future research directions, such as the design of novel structures, performance optimization, and exploration of practical applications, aiming to provide references and inspirations for researchers in related fields.

Synthesis, photophysics and two-photon absorption of imidazole-centred tripodal chromophores

Tripodal push-pull chromophores with D-(π-A)3 arrangement were synthesized using 1-methyl-2,4,5-triphenyl-1H-imidazole as a central electron donor, and their thermal, electrochemical, photophysical and non-linear optical properties were studied and corroborated with quantum-chemical calculations. Their facile synthesis involved Suzuki-Miyaura and Knoevenagel reactions, allowing the installation of various peripheral electron acceptors such as formyl, cyano, ester, trifluoromethyl and more complex moieties such as malonic/acetic acid derivatives, indan-1,3-dione and rhodanine. All phenyl rings appended at the central imidazole core were more or less twisted depending on the peripheral substitution. Although imidazole undergoes reversible one-electron oxidation, peripheral acceptors are reduced irreversibly in a multi-electron process. This behaviour is further seen as a variation of the LUMO, while the HOMO remained almost unaltered across the whole series. TD-DFT calculations revealed centrifugal charge transfer from the central imidazole to all C2, C4 and C5 branches occupied by the LUMO, LUMO+1 and LUMO+2. The HOMO-LUMO gap is tuneable within the range of 3.55-2.31 eV, while the longest-wavelength absorption/emission maxima were found within the broad range of 304-448/393-612 nm. Although the absorption spectra are solvent-independent, the emission depends strongly on the solvent polarity and the electron-withdrawing power of the peripheral acceptors. Extended chromophores with complex electron acceptors were investigated as two-photon absorbers, revealing relatively good cross-section values of up to 521 GM and a figure-of-merit (ΦF × δ2PA) of around 190 GM.

Receptor-free phenothiazine derivative as fluorescent probe for picric acid: Investigation of the inner filter effect channel

In this study, a highly fluorescent and receptor-free phenothiazine derivative (PDAB) was developed to detect picric acid. A combination of steady-state and time-resolved fluorescence studies was conducted to examine the excited state behavior of PDAB with picric acid in solution. The PDAB probe displayed a significant degree of selectivity and was highly sensitive to picric acid, with an extremely low detection limit of 9.82 nM. Time-resolved fluorescence quenching studies exhibit direct evidence of an inner filter effect-based sensing mechanism. Using the Parker equation, a thorough analysis was done to correct the inner filter effect on the sensing of picric acid. Overall, these studies provide critical information on the sensing mechanism for picric acid detection.

3D printed optical sensor for highly sensitive detection of picric acid using perovskite nanocrystals and mechanism of photo-electron transfer

Hand-held, compact and portable sensors for on-site detection of environmental contaminants are in high demand for industry 4.0. Here, we have developed a sensor based on luminescent organic-inorganic metal halide hybrid perovskites nanocrystals (CH₃NH₃PbBr₃) with p-xylylenediamine as an additional capping agent for highly sensitive and selective detection of picric acid (PA), with a good linear range of 1.8 μM-14.3 μM achieving detection of limit (LOD) of 0.3 μM. The electrostatic interaction between PA and the capping ligand of perovskite nanocrystals resulted in significant fluorescence quenching, as revealed by the steady-state and time-resolved spectroscopy. The applicability of the developed sensor for PA detection was validated with a 3D printed device integrating surface mounting device (SMD) and paper microfluidics. This prototype device was successfully applied as a fluorescence turn-off sensor to detect PA, showing great potential for on-site detection. This 3D-printed paper-based microfluidic optical sensor proved very efficient for naked-eye detection of PA with an inbuilt excitation source, avoiding the requirement of expensive and complex instrumentation.