Functionalization of BODIPY Dyes with Additional C-N Double Bonds and Their Applications

BODIPY (4-bora-3a,4a-diaza-s-indacene) dyes are regarded as highly useful compounds due to their rich photophysical properties, stability, and ease of functionalization. In recent years, hot topics studied with this class of compounds are targeted photodynamic therapy, photothermal therapy, fluorescent bioimaging agents, structural modification of the BODIPY core, synthesis of BODIPY analogs, and BODIPY-based supramolecular constructs. This review covers the advances in BODIPY structures substituted with additional carbon-nitrogen double bonds, namely imines, hydrazones, oximes, and related derivatives for various applications. Works based on fluorescent indicators of anions, cations, and neutral molecules are included in this review. In addition, the use of such structures for pharmaceutical applications, photodynamic therapy, fluorescent switches, and fluorescent building blocks are also investigated. In addition to covering the major literature within the mentioned subclass, design principles, working mechanisms, and outlooks are also provided to enlighten forthcoming promising efforts. With this work, we aim to provide insights about the synthesis, photophysical properties, contribution of C=N bonds to a class of dye, and possible areas of use and stimulate researchers to present new ideas and overcome the current problems using these derivatives.

Dicoumarin with dimethyl thiocarbamate in the fluorescent detecting for Au3+ in water and cells

Gold ions have high activity and cytotoxicity completely different from elemental gold. It is necessary and critical to develop Au³⁺ detection tools that are easy to operate, intuitive, inexpensive, and non-destructive testing. Here, we propose a novel two-photon fluorescent probe named DA for detecting Au³⁺, which is a rare combination of dicoumarin with dimethylthiocarbamate for the first time. Based on the PET mechanism, DA turns-on the fluorescence to yellow-green after specifically binds to Au³⁺, and the reaction is completed within 5 min. The detection limit is as low as 27.60 nM. Simultaneously, DA achieved qualitative and quantitative detection of Au³⁺ in environmental water samples, and fluorescence imaging of Au³⁺ in biological cells.

Effect of conjugated system extension on structural features and electron-density distribution in charge-transfer difluoroborates

A comparative structural study of two related donor-acceptor pyridine-based BF₂ complexes, namely, 3-(dimethylamino)-1,1-difluoro-1H-pyrido[1,2-c][1,3,5,2]oxadiazaborinin-9-ium-1-uide, C₈H₁₀BF₂N₃O (1), and 3-{(1E,3E)-4-[4-(dimethylamino)phenyl]buta-1,3-dien-1-yl}-1,1-difluoro-1H-pyrido[1,2-c][1,3,5,2]oxadiazaborinin-9-ium-1-uide, C₁₈H₁₈BF₂N₃O (2), containing a dimethylamino group and either the shortest (in 1) or the longest (in 2) charge-transfer path known until now in this family of compounds, is presented. Single-crystal X-ray diffraction analysis supported by computational investigations shed more light on these systems, indicating, among other aspects, the predominance of C-H...F contacts in 1, the formation of antiparallel dimers held together by π-π interactions in both compounds, and the involvement of fused BF₂-bearing rings in the charge-transfer process.

A “turn-on” fluorescent and colorimetric chemodosimeter for selective detection of Au3+ ions in solution and in live cells via Au3+-induced hydrolysis of a rhodamine-derived Schiff base

A chromogenic and “off–on” fluorogenic chemodosimeter (L) based on a naphthalene–rhodamine B derivative was designed, synthesized and characterized for the selective and sensitive detection of Au³⁺ ions in mixed acetonitrile aqueous media.

BODIPY-Derived Polymeric Chemosensor Appended with Thiosemicarbazone Units for the Simultaneous Detection and Separation of Hg(II) Ions in Pure Aqueous Media

Developing a simple and cheap analytical method for the selective detection and quantitative separation of toxic ions present in aqueous media is the biggest challenge faced by the chemosensing research community. Here, a 5,5-difluoro-1,3,7,9-tetramethyl-10-phenyl-5 H-dipyrrolo-diazaborinine-derived water-soluble polymer integrated with thiosemicarbazone units was rationally designed and synthesized for the simultaneous detection and separation of Hg(II) ions in pure aqueous solution. The water-soluble polymer scaffold poly( N, N'-dimethyl acrylamide- co-5,5-difluoro-1,3,7,9-tetramethyl-10-phenyl-5 H-dipyrrolo-diazaborinine-2-carbaldehyde) was synthesized by reversible addition-fragmentation chain transfer polymerization, followed by post-polymerization modification with thiosemicarbazide, leading to the formation of the target probe, P1. The nonemitting P1 exhibited bright yellow emission upon exposure to Hg(II) ions, with a limit of detection as low as 0.37 μM. This turn-on emission behavior triggered by Hg(II) ions might originate from the suppression of isomerization around the C═N bond of the thiosemicarbazone moiety caused by the formation of a coordination complex between P1 and Hg(II) ions. In addition, P1 displayed excellent selectivity toward Hg(II) ions over other metal cations. Finally, the selective removal of Hg(II) ions from an aqueous solution containing various metal ions was achieved by precipitation, which is probably caused by the fact that coordination complexes whereby Hg(II) ions acted as bridgeheads between P1 molecules had formed.

Selective and reversible recognition of Hg2+ ions by Tetrathia[22]porphyrin(2.1.2.1)

Interestingly, neutral tetrathia[22]porphyrin(2.1.2.1) (TTP) acts as an efficient chemosensor for the detection of Hg²⁺ ions at ppb concentration. Consequent to binding the molecular plane of TTP bends and it has been supported by the DFT calculations. A rise in levelling off tail is observed in the electronic absorption spectrum in the presence of Hg²⁺ ions, which is suggestive of metal induced macrocyclic self-assembly and is further substantiated by the SEM, TEM and particle size measurement studies.

Applications of Nanomaterials Based on Magnetite and Mesoporous Silica on the Selective Detection of Zinc Ion in Live Cell Imaging

Functionalized magnetite nanoparticles (FMNPs) and functionalized mesoporous silica nanoparticles (FMSNs) were synthesized by the conjugation of magnetite and mesoporous silica with the small and fluorogenic benzothiazole ligand, that is, 2(2-hydroxyphenyl)benzothiazole (hpbtz). The synthesized fluorescent nanoparticles were characterized by FTIR, XRD, XRF, ¹³C CP MAS NMR, BET, and TEM. The photophysical behavior of FMNPs and FMSNs in ethanol was studied using fluorescence spectroscopy. The modification of magnetite and silica scaffolds with the highly fluorescent benzothiazole ligand enabled the nanoparticles to be used as selective and sensitive optical probes for zinc ion detection. Moreover, the presence of hpbtz in FMNPs and FMSNs induced efficient cell viability and zinc ion uptake, with desirable signaling in the normal human kidney epithelial (Hek293) cell line. The significant viability of FMNPs and FMSNs (80% and 92%, respectively) indicates a potential applicability of these nanoparticles as in vitro imaging agents. The calculated limit of detections (LODs) were found to be 2.53 × 10⁻⁶ and 2.55 × 10⁻⁶ M for Fe₃O₄-H@hpbtz and MSN-Et₃N-IPTMS-hpbtz-f1, respectively. FMSNs showed more pronounced zinc signaling relative to FMNPs, as a result of the more efficient penetration into the cells.

BODIPY-derived multi-channel polymeric chemosensor with pH-tunable sensitivity: selective colorimetric and fluorimetric detection of Hg2+ and HSO4− in aqueous media

A water-soluble BODIPY-containing polymeric chemosensor was synthesized for the selective colorimetric and turn-on fluorimetric detection of Hg²⁺ and HSO₄⁻ ions, respectively, in 100% aqueous media at physiological pH.

Design of a two-photon fluorescent probe for selective recognition of Au(III) over Au(I) and its application of imaging in vitro and in vivo

A highly selective two-photon fluorescent probe (PyCM-1) for Au³⁺ was developed with distinct "turn on" fluorescence response, low detection limit (22nM) and large two-photon absorption cross-sections (696 GM at 860nm). Its high selectivity for Au³⁺ over Au⁺ was achieved via the modification on the type of coordination atoms in the Schiff base receptor. Co-staining experiments showed that the probe PyCM-1 could co-localize specifically with mitochondria. Moreover, the two-photon confocal fluorescence imaging results demonstrated the probe's capability for visualizing Au³⁺in vitro and in vivo.

Highly selective ratiometric fluorescent probe based on diketopyrrolopyrrole for Au3+: an experimental and theoretical study

A diketopyrrolopyrrole-based fluorescent probe 1 was explored as a ratiometric probe for selective detection of Au³⁺, with the detection limit of 18 nM.

A novel triphenylamine-BODIPY dendron: click synthesis, near-infrared emission and a multi-channel chemodosimeter for Hg2+ and Fe3+

A novel near-infrared emission triphenylamine-BODIPY dendron for Hg²⁺ and Fe³⁺ detection, fluorescent nanoparticle and living cell imaging.

A BODIPY-based fluorescent probe for ratiometric detection of gold ions: utilization of Z-enynol as the reactive unit

Using an irreversible intramolecular cyclisation pathway triggered by gold ions, a boron-dipyrromethene (BODIPY) based fluorescent probe integrated with a reactive Z-enynol motif responds selectively to gold ions.

Indole-BODIPY: a “turn-on” chemosensor for Hg2+ with application in live cell imaging

A noval BODIPY probe appended with electron rich indolic units at the β-pyrrolic position, acts as a ‘turn-on’ chemosensor for Hg²⁺ in solution as well as in HeLa cells.

A novel BODIPY-Schiff base-based colorimetric and fluorometric dosimeter for Hg2+, Fe3+ and Au3+

A simple Schiff base-based multi-targets dosimeter for Hg²⁺, Fe³⁺ and Au³⁺ has been reported.

A turn-on fluorescent pyrene-based chemosensor for Cu(ii) with live cell application

A pyrene-based fluorescent sensor (PHP) was synthesized for Cu(ii) detection.