Benzo[c,d]indole-Containing Aza-BODIPY Dyes: Asymmetrization-Induced Solid-State Emission and Aggregation-Induced Emission Enhancement as New Properties of a Well-Known Chromophore

One-pot synthesis of azabora[6]helicene by a Schiff base forming reaction

Azabora[6]helicene as a new heterohelicene analogue was synthesized by a one-pot reaction of commercially available 2,6-diaminopyridine and benzo[c,d]indole-2(1H)-one and subsequent boron coordination. While the single-crystal X-ray diffraction analysis elucidated a helical structure in the solid state, a dynamic helicity inversion was observed in solution.

Facile Synthesis of Asymmetric aza-Boron Dipyrromethene Analogues Bearing Quinoxaline Moiety

An asymmetric aza-BODIPY analogue bearing quinoxaline moiety was synthesized via a titanium tetrachloride-mediated Schiff-base-forming reaction of 6,7-dimethyl-1,4-dihydroquinoxaline-2,3-dione and benzo[d]thiazol-2-amine. This novel aza-BODIPY analogue forms a complementary hydrogen-bonded dimer due to the quinoxaline moiety in the crystal structure. It also shows intense absorption and fluorescence, with fluorescence quantum yields close to unity. The electrochemical measurements and the DFT calculations revealed the presence of the low-lying HOMO, which benefits their potential applications as an electron-transporting material.

Recent Advances in the Synthesis of Borinic Acid Derivatives

Borinic acids [R2B(OH)] and their chelate derivatives are a subclass of organoborane compounds used in cross-coupling reactions, catalysis, medicinal chemistry, polymer or optoelectronics materials. In this paper, we review the recent advances in the synthesis of diarylborinic acids and their four-coordinated analogs. The main strategies to build up borinic acids rely either on the addition of organometallic reagents to boranes (B(OR)3, BX3, aminoborane, arylboronic esters) or the reaction of triarylboranes with a ligand (diol, amino alcohol, etc.). After general practical considerations of borinic acids, an overview of the main synthetic methods, their scope and limitations is provided. We also discuss some mechanistic aspects.

Triphenylborane in Metal-Free Catalysis

The development and application of new organoboron reagents as Lewis acids in synthesis and metal-free catalysis have dramatically expanded over the past 20 years. In this context, we will show the recent uses of the simple and relatively weak Lewis acid BPh₃-discovered 100 years ago-as a metal-free catalyst for various organic transformations. The first part will highlight catalytic applications in polymer synthesis such as the copolymerization of epoxides with CO₂, isocyanate, and organic anhydrides to various polycarbonate copolymers and controlled diblock copolymers as well as alternating polyurethanes. This is followed by a discussion of BPh₃ as a Lewis acid component in the frustrated Lewis pair (FLP) mediated cleavage of hydrogen and hydrogenation catalysis. In addition, BPh₃-catalyzed reductive N-methylations and C-methylations with CO₂ and silane to value-added organic products will be covered as well along with BPh₃-catalyzed cycloadditions and insertion reactions. Collectively, this mini-review showcases the underexplored potential of commercially available BPh₃ in metal-free catalysis.

Palladium-Catalyzed Preparation of N-Substituted Benz[c,d]indol-2-imines and N-Substituted Amino-1-naphthylamides

Here, we report a novel and facile protocol for the synthesis of benz[c,d]indol-2-imines via palladium-catalyzed C-C and C-N coupling of 8-halo-1-naphthylamines with isocyanides in a single step. The reaction features broad substrate scopes and mild conditions, providing an efficient alternative for the construction of antiproliferative agents and BET bromodomain inhibitors. If 0.1 mL of H₂O was added to this reaction, the N-substituted amino-1-naphthylamides could be obtained easily.

Aromaticity-Enhanced pH-Responsive Electrochemiluminescence of Cyclopentadienols

Due to significantly tackling the problems of aggregation-caused quenching and water insolubility, aggregation-induced emission electrochemiluminescence (AIE-ECL) has emerged as a research highlight in aqueous detection and sensing. Herein, we reported a series of cyclopentadienols featuring excellent AIE-ECL properties on the basis of an enhanced aromaticity strategy. In detail, substituents profoundly determined ECL emission by affecting the characteristic absorption peak intensity ratio in UV-vis spectra and lowest unoccupied molecular orbital (LUMO)-highest occupied molecular orbital (HOMO) energies. It was found that 1,2,3,4,5-pentafluorophenyl cyclopentadienol (PFCD) containing an electron-withdrawing fluorine substituent, the maximum R/B band ratio, and a smaller LUMO-HOMO band gap demonstrated the best ECL performance. Meanwhile, such an AIE-ECL system displayed a wide response range toward pH (4-12) with a good linear relationship. Our research not only enriched polycyclic aromatic hydrocarbon-based AIE-ECL systems but also established an efficient pH sensor in the aqueous phase.

Synthesis and photophysical properties of nitrated aza-BODIPYs

A series of nitrated aza-BODIPYs on the 2- and 6-positions were regioselectively synthesized and their photophysical properties were examined.

A novel domino protocol for three-component synthesis of new dibenzo[e,g]indoles: flexible intramolecular charge transfers

New and electronically interesting 2-aryl-3-nitrodibenzo[e,g]indoles were synthesized effectively via a hitherto unreported three-component domino reaction under catalysis of a superparamagnetic nano-composite.

AIE-Active Difluoroboron Complexes with N,O-Bidentate Ligands: Rapid Construction by Copper-Catalyzed C-H Activation

The development of organic materials with high solid-state luminescence efficiency is highly desirable because of their fundamental importance and applicability in optoelectronics. Herein, a rapid construction of novel BF2 complexes with N,O-bidentate ligands by using Cu(BF4 )2 •6H2 O as a catalyst and BF2 source is disclosed, which avoids the need for pre-composing the N,O-bidentate ligands and features a broad substrate scope and a high tolerance level for sensitive functional groups. Moreover, molecular oxygen is employed as the terminal oxidant in this transformation. A library of 36 compounds as a new class of BF2 complexes with remarkable photophysical properties is delivered in good to excellent yields, showing a substituent-dependency on the photophysical properties, derived from the π-π* character of the photoexcited state. In addition, aggregation-induced emission (AIE) is observed and quantified for the brightest exemplars. The excited state properties are fully investigated in solids and in THF/H2 O mixtures. Hence, a new series of photofunctional materials with variable photophysical properties is reported, with potential applications for sensing, bioimaging, and optoelectronics.

Aggregation-Induced Circularly Polarized Luminescence from Boron Complexes with a Carbazolyl Schiff Base

A variety of carbazolyl-appended Schiff bases were readily synthesized from 1-formylcarbazoles and aniline derivatives. Boron complexation of the resulting ligands allowed for facile preparation of new carbazole-based BODIPY analogues showing solid-state fluorescence. Furthermore, some dyes were converted into chiral compounds through the Et₂ AlCl-mediated incorporation of a binaphthyl unit. The chiral dyes showed aggregation-induced fluorescence and circularly polarized luminescence (CPL) with the Φ_F and g_lum of up to 0.22 and -3.5×10^-3 , respectively, in the solid state. The solid-state fluorescence and CPL were well characterized by the crystal packing analyses and DFT calculations.

A Family of BODIPY-like Highly Fluorescent and Unsymmetrical Bis(BF2) Pyrrolyl-Acylhydrazone Chromophores: BOAPY

A new family of pyrrolyl-acylhydrazones anchored with two BF₂ units, named BOAPY, have been developed as BODIPY-like and unsymmetrical bis(BF₂) chromophores via a simple one-pot reaction. The easily accessible scaffold enjoys excellent diversity due to the structural versatilities of 2-formylpyrroles and acylhydrazines. BOAPYs exhibit good molar absorption coefficients, large Stokes shifts, and excellent chemical stability. More importantly, most of them display excellent fluorescence quantum yields both in solution and the solid state (up to 0.88 and 0.64, respectively).

Red-emitting boron difluoride complexes with a mega-large Stokes shift and unexpectedly high fluorescence quantum yield

Introduction of a tetrahydroquinoxaline donor into boron difluoride complexes largely extended their emissions (617–684 nm), highly improved their fluorescence quantum yields (up to 0.68) and greatly increased their Stokes shifts (up to 209 nm).

Rational design of pyrrolopyrrole-aza-BODIPY-based acceptor–donor–acceptor triads for organic photovoltaics application

Acceptor–donor–acceptor triads consisting of diketopyrrolopyrrole (DPP) or pyrrolopyrrole aza-BODIPY (PPAB) or both as acceptors and cyclopentadithiophene as a donor were rationally designed for near infrared (NIR) photovoltaics application.

Recent chemo-/biosensor and bioimaging studies based on indole-decorated BODIPYs

BODIPY is an important fluorophores due to its enhanced photophysical and chemical properties including outstanding thermal/photochemical stability, intense absorption/emission profiles, high photoluminescence quantum yield, and small Stokes' shifts. In addition to BODIPY, indole and its derivatives have recently gained attention because of their structural properties and particularly biological importance, therefore these molecules have been widely used in sensing and biosensing applications. Here, we focus on recent studies that reported the incorporation of indole-based BODIPY molecules as reporter molecules in sensing systems. We highlight the rationale for developing such systems and evaluate detection limits of the developed sensing platforms. Furthermore, we also review the application of indole-based BODIPY molecules in bioimaging studies. This article includes the evaluation of indole-based BODIPYs from synthesis to characterization and a comparison of the advantages and disadvantages of developed reporter systems, making it instructive for researchers in various disciplines for the design and development of similar systems.

Recent Progress of BODIPY Dyes With Aggregation-Induced Emission

With the development of organic optoelectronic materials and bioimaging technology, to exploit organic luminescent materials with high luminescent efficiency in aggregation-state has become a research hotspot. BODIPYs have become one of the research objects of this kind of material because of their obvious advantages. This review focuses on the design and synthesis of AIE-type BODIPYs, the mechanism of AIE properties and their applications in recent years. Through classification, analysis, and summary, this review aims to explore the structure-activity relationship of AIE-type BODIPYs and to provide ideas for the further design and potential applications of AIE-active fluorescent materials.

aza-BODIPY synthesis towards vis/NIR functional chromophores based on a Schiff base forming reaction protocol using lactams and heteroaromatic amines

The Schiff base forming reaction of lactams and heteroaromatic amines led to creation of a new class of aza-BODIPY analogues as visible and near infrared functional chromophores.

Benzo[4,5]thiazolo[3,2- c][1,3,5,2]oxadiazaborinines: Synthesis, Structural, and Photophysical Properties

A family of highly emissive benzo[4,5]thiazolo[3,2- c][1,3,5,2]oxadiazaborinines, conjugated with the donor 4-dimethylaminophenyl group, was designed and synthesized. Their photophysical, both in solution and in the solid state, and structural properties were investigated. The influence of donor and acceptor substituents (R) in the benzothiazole unit on photophysical properties of complexes was found out. The tetrafluorobenzothiazole analogue exhibits nonbonded nuclear spin-spin coupling between fluorines from the BF₂ group and α-fluorine atom at the benzene ring. Additionally, this boron complex demonstrates a comparatively high solid-state fluorescence quantum yield (Φ = 0.34).

Time dependent aggregation induced emission enhancement and the study of molecular packing in closely related azo-phenol BODIPY species

Fluorescent azo-phenol BODIPYs (1-3) have been obtained by the substituent (-OCH₃/-CH₃) directed synthesis of ortho (L1) and para (L2-L3) azo-phenol aldehydes. These display aggregation caused quenching (ACQ, 1) and aggregation induced emission enhancement (AIEE, 2 and 3) depending on the position of azo relative to the phenolic hydroxyl group. An intriguing time dependent morphological transition from nanospheres to ordered nanorods and subsequent emission changes in AIEE active azo-phenol BODIPYs have been successfully realized by time dependent fluorescence, scanning electron (SEM), transmission electron (TEM) and fluorescence optical microscopy (FOM) studies. The existence of one-dimensional (1D) nanorods as ultimate species in these compounds (2-3) has been supported by crystal packing patterns. Diverse aggregated forms and hierarchical nanostructures have been related to variable extents of fluorescence enhancement. The plausible charge transfer process and its role in AIEE have been supported by DFT studies.

N,O π-Conjugated 4-Substituted 1,3-Thiazole BF2 Complexes: Synthesis and Photophysical Properties

A series of 1,3-thiazole-based organoboron complexes has been designed and synthesized by acylation of 2-amino 4-subsituted 1,3-thiazoles with (4-dimethylamino)benzoyl chloride and the subsequent BF₂ complexation reaction. The influence of substituents in position 4 of the thiazole ring on photophysical properties of the complexes has been investigated. Synthesized thiazolo[3,2-c][1,3,5,2]oxadiazaborinines mainly showed intensive fluorescence in solutions. Complex with a 4,5-unsubstituted thiazole unit demonstrated an aggregation induced emission (AIE) effect and a very high fluorescent quantum yield (94%) in the solid state because of the inhibition of π-π/π-n interactions in the molecular packing.

Electro-click construction of hybrid nanocapsule films with triggered delivery properties

Nanocapsule films composed of hollow PAA/IONPs hybridosomes were covalently assembled in one-pot by electro-click, enabling the encapsulation and triggered release of bodipy.

N-Bridged Annulated BODIPYs: Synthesis of Highly Fluorescent Blueshifted Dyes

A series of novel BODIPY dyes has been prepared through the introduction of an N-bridged annulated meso-phenyl ring at one of the β-positions of the BODIPY core. An unusual blueshift of the main spectral bands is observed, since the fusion of a meso-substituent results in a marked relative destabilization of the LUMO. The greater rigidity of the ring-fused structure leads to very high fluorescence quantum yields. The position of the main spectral bands can be fine-tuned by introducing electron withdrawing and donating groups onto the meso-phenyl ring.

Synthesis of carbazole-based BODIPY dimers showing red fluorescence in the solid state

Carbazole-based BODIPY dimers 2a–g were synthesized via direct arylation.

Carbazole-based BODIPYs with ethynyl substituents at the boron center: solid-state excimer fluorescence in the VIS/NIR region

Carbazole-based BODIPYs 1–6 with several different substituents at the boron atom site were synthesized.

Aza boron-pyridyl-isoindoline analogues: synthesis and photophysical properties

The synthesis and properties of four aza boron pyridyl-isoindoline analogues that differ in the position of fused benzene ring annelation on the pyridyl moiety is reported.

Synthesis and spectroscopic properties of novel N–N linked bis-(diphenylboron) complexes

Novel five-membered-ring and six-membered-ring bis-(diphenylboron) complexes are reported.

Preservation of main-chain conjugation through BODIPY-containing alternating polymers from electronic interactions with side-chain substituents by cardo boron structures

This manuscript describes the synthesis and electronic structures of the modified boron dipyrromethene derivatives containing cardo boron.

Non-symmetric benzo[b]-fused BODIPYs as a versatile fluorophore platform reaching the NIR: a systematic study of the underlying structure–property relationship

Ten newly synthesized non-symmetric benzo[b]-fused BODIPYs are compared with an extended series of nine related families (23 compounds) to gain insights into their structure–property relationship.

Azadipyrromethenes: from traditional dye chemistry to leading edge applications

The journey of azadipyrromethenes from accidental dye chemistry to a compound class with widely applicable near infrared photophysical properties is documented.