Systematic theoretical investigation of two novel molecules BtyC-1 and BtyC-2 based on ESIPT mechanism

Inexperiment, Song et al. have successfully synthesizedtwo novel molecules BtyC-1 and BtyC-2 and observedasingle and dual fluorescence peaks in these two molecules respectively. (Song et al. Tetrahedron Lett. 2019, 60, 1696-1701) However, they still lack a detailed and reasonable theoretical explanation. Then we wonder why these two similar structures behave so much differently? In this work, we focus on explaining the photochemical and photophysical properties of BtyC-1 and BtyC-2 by studying the excited state intramolecular proton transfer (ESIPT) mechanisms. Based on the optimized geometric configurations, the calculated infrared spectra indicate the intramolecular hydrogen bonding interactions are heightened in their excited states. The frontier molecular orbitals reflect the charge redistribution in photoinduced process, which explains that the driving force of ESIPT process is provided by enhanced hydrogen bonding interactions. In the meantime, the calculations of potential energy curves vividly explain the principle of the experimental dual fluorescence phenomenon. The analysis of Mulliken charges deepens the discussion of molecular structures on the potential energy barriers. Calculated absorption spectra via using density functional theory and emission spectra via using time-dependent density functional theory are consistent with the experimental data, which confirms the correctness of our calculation methods. The reduced density gradient isosurfaces help us distinguish the complex non-covalent bonds. Base on the above analyses, we conclude that there is no stable structure for BtyC-1 in excited state, which make it occur the ESIPT reaction spontaneously. BtyC-2 exists a stable normal structure in excited state. Its dual fluorescence signals are emitted by its normal and isomer structures, respectively.

A novel chemosensor for the distinguishable detections of Cu2+ and Hg2+ by off-on fluorescence and ratiometric UV-visible absorption

A novel dual-functional chemosensor, derived from the conjugation of rhodamine B with a quinoline derivative (RHQ), was firstly synthesized with high efficiency and cost-effectiveness for the distinguishable detections of Cu²⁺ and Hg²⁺ via ring-opening and ring-forming mechanism. The chemosensor exhibits highly selective and distinguishable responses for Cu²⁺ and Hg²⁺ in CH₃CN-H₂O (4:1, v/v) with off-on fluorescence and ratiometric ultraviolet-visible (UV-Vis) absorption changes. Additionally, Cu²⁺ is identified by opening a rhodamine spirocycle with a UV-Vis absorption band, at around 560 nm and fluorescence turn-on. Interestingly, Hg²⁺ is discerned by opening the rhodamine spirocycle and by generating a new special cycle for the quinoline unit. Resultantly, there were two UV-Vis absorption bands at around 365 nm and 560 nm, which were accompanied by fluorescence turn-on. Moreover, the chemosensor can quantitatively detect Cu²⁺ and Hg²⁺ by off-on fluorescence and ratiometric UV-Vis absorption changes, respectively. Furthermore, the chemosensor with low cytotoxicity could be successfully administered to monitor Cu²⁺ and Hg²⁺ in living cells. This work may pay the way for the development of dual-functional chemosensor for quantificationally detecting metal ions in environmental and biological systems.

Recyclable fluorescent chemodosimeters based on 8-hydroxyquinoline derivatives for highly sensitive and selective detection of mercury(II) in aqueous media and test strips

Four novel highly selective 8-hydroxyquinoline-based fluorescent chemodosimeters (1-4) were synthesized for the rapid analysis of Hg²⁺ in aqueous solution and on paper strips, which probably attributed to the excited state intramolecular proton transfer (ESIPT) process. Chemodosimeter 1 was evaluated as a Hg²⁺-ratiometric fluorescent sensor while others (2, 3 and 4) displayed fluorescence turn-on response for Hg²⁺ among the various survey metal ions. We demonstrated that chemodosimeters (1-4) could recognized Hg²⁺ ions based on a 1:1 stoichiometric binding event with fast detection time. More importantly, the detection limits for Hg²⁺ could reach at 10^-9 M level except chemodosimeter 1 (4.05 × 10^-8 M). In addition, it was found that chemodosimeters (1-4) were recycled efficiently because the Hg²⁺ induced emission spectra were reversed after adding NaBH₄. Finally, these four sensors were successfully applied for fabrication of simple device test strips for rapid and on-site detection of Hg²⁺ ions.

Aggregation-induced emission enhancement (AIEE)-active tetraphenylethene (TPE)-based chemosensor for Hg2+ with solvatochromism and cell imaging characteristics

An aggregation-induced emission enhancement (AIEE)-active fluorescent sensor based on a tetraphenylethene (TPE) unit has been successfully designed and synthesized. Interestingly, the luminogen could detect Hg²⁺ with high selectivity in an acetonitrile solution without interference from other competitive metal ions, and the detection limit was 7.46 × 10⁻⁶ mol L⁻¹. Furthermore, the luminogen also showed interesting solvatochromic behavior and superior cell imaging performance.

A TPE-based AIEE-active fluorescent sensor for Hg²⁺ was synthesized. Furthermore, it showed solvatochromism and cell imaging characteristics.

A novel and effective benzo[d]thiazole-based fluorescent probe with dual recognition factors for highly sensitive and selective imaging of cysteine in vitro and in vivo

Double recognition groups significantly improved the selectivity of a fluorescent probe to Cys in living cells.

Li+-Induced fluorescent metallogel: a case of ESIPT-CHEF and ICT phenomenon

A fluorescent metallogel has been synthesized from non-fluorescent ingredients viz. the smallest possible LMW aromatic symmetrical gelator 1 and LiOH, whereas KOH produces a non-fluorescent solution, and regioisomer 2 with LiOH shows an ICT assisted fluorescent precipitate rather than a metallogel.

A two-photon ratiometric ESIPT probe for fast detection and bioimaging of palladium species

A two-photon ratiometric ESIPT probe for fast detection of palladium species, which can be used for bioimaging has been designed.

A reversible ratiometric two-photon lysosome-targeted probe for real-time monitoring of pH changes in living cells

A reversible ratiometric two-photon lysosome-targeted probe that can monitor real-time pH changes in living cells.

A two-photon ratiometric ESIPT probe for the discrimination of different palladium species and its application in bioimaging

A two-photon ratiometric ESIPT probe for the discrimination of different palladium species which could be used for bioimaging.

Lead ion induced chemodosimeter approach of a tripodal hydroxyl-quinoline based phospho-ester through P–O bond cleavage

Pb²⁺ induced phosphoester hydrolysis followed by the formation of a penta coordinated chelate complex of lead.

Harvesting red fluorescence through design specific tuning of ICT and ESIPT: an efficient optical detection of cysteine and live cell imaging

In this work, a 2-(2-hydroxyphenyl)benzothiazole (HBT)-based ratiometric fluorescent probe exhibiting coupling between the ICT and ESIPT mechanisms was exploited for the optical sensing of cysteine and successfully utilised in the bio-imaging of cysteine in HeLa cells.

A water-soluble colorimetric two-photon probe for discrimination of different palladium species and its application in bioimaging

A novel water-soluble colorimetric two-photon chemodosimeter for discrimination of different palladium species and its application in bioimaging.

Single excited state intramolecular proton transfer (ESIPT) chemodosimeter based on rhodol for both Hg2+ and OCl−: ratiometric detection with live-cell imaging

We have synthesised a ratiometric fluorescence chemodosimeter, STBR, for the detection of Hg²⁺ and OCl⁻ in one platform over other cations, anions and oxidants in aqueous solution.