Construction of Boron Difluoride Complexes with Asymmetric N,N'-Bidentate Ligands

Boron difluoride (BF2) complexes with asymmetrical N,N'-bidentate ligands have received increasing attention due to their fascinating properties and broad applications. They are generally constructed in two steps: ligand formation, followed by boron complexation. This review focuses on categorizing these BF2 complexes based on the key synthetic strategies that have been applied in the ligand formation steps. The post-functionalization, properties and applications of different types of BF2 complexes are presented. Their challenges and opportunities are also discussed. This should help the future rational design and synthesis of BF2 complexes with intriguing properties and practical applications.

Advancements in boron difluoride formazanate dyes for biological imaging

In the past decade, boron difluoride formazanate dyes have gained considerable attention due to their redox activity, high absorption and emission intensities, chemical stability across a broad range of conditions, and the ease to fine-tune their optical and electronic characteristics. Over the past five years, boron difluoride formazanate dyes have demonstrated their extended emission wavelengths in the near-infrared region, suggesting their potential applications in the field of biological imaging. This review provides an overview of the evolution of boron difluoride formazanate dyes, encompassing the structural variations and corresponding optical properties, while also highlighting their current applications in biological imaging fields.

Tuning the Properties of Donor-Acceptor and Acceptor-Donor-Acceptor Boron Difluoride Hydrazones via Extended π-Conjugation

Molecular materials with π-conjugated donor-acceptor (D-A) and acceptor-donor-acceptor (A-D-A) electronic structures have received significant attention due to their usage in organic photovoltaic materials, in organic light-emitting diodes, and as biological imaging agents. Boron-containing molecular materials have been explored as electron-accepting units in compounds with D-A and A-D-A properties as they often exhibit unique and tunable optoelectronic and redox properties. Here, we utilize Stille cross-coupling chemistry to prepare a series of compounds with boron difluoride hydrazones (BODIHYs) as acceptors and benzene, thiophene, or 9,9-dihexylfluorene as donors. BODIHYs with D-A and A-D-A properties exhibited multiple reversible redox waves, solid-state emission with photoluminescence quantum yields up to 10%, and aggregation-induced emission (AIE). Optical band gaps (or highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gaps) determined for these compounds (2.02-2.25 eV) agree well with those determined from cyclic voltammetry experiments (2.05-2.42 eV). The optoelectronic properties described herein are rationalized with density functional theory calculations that support the interpretation of the experimental findings. This work provides a foundation of understanding that will allow for the consideration of D-A and A-D-A BODIHYs to be incorporated into applications (e.g., organic electronics) where fine-tuning of band gaps is required.

Recent advances in the synthesis of luminescent tetra-coordinated boron compounds

Tetra-coordinated boron compounds offer a plethora of luminescent materials. Different chelation around the boron center (O,O-, N,C-, N,O-, and N,N-) has been explored to tune the electronic and photophysical properties of tetra-coordinated boron compounds. A number of fascinating molecules with interesting properties such as aggregation induced emission, mechanochromism and tunable emission by changing the solvent polarity were realised. Owing to their rich and unique properties, some of the molecules have shown applications in making optoelectronic devices, probes and so on. This perspective provides an overview of the recent developments of tetra-coordinated boron compounds and their potential applications.

Water-soluble Al(iii), Fe(iii) and Cu(ii) formazanates: synthesis, structure, and applications in alkane and alcohol oxidations

The synthesis, structure and catalytic performance of water-soluble Al(iii), Fe(iii) and Cu(ii) formazanates in the oxidation of cyclohexane and cyclohexanol to the coresponding organic products are reported.

Band Gap Engineering in Acceptor-Donor-Acceptor Boron Difluoride Formazanates

π-Conjugated molecules with acceptor-donor-acceptor (A-D-A) electronic structures make up an important class of materials due to their tunable optoelectronic properties and applications in, for example, organic light-emitting diodes, nonlinear optical devices, and organic solar cells. The frontier molecular orbital energies, and thus band gaps, of these materials can be tuned by varying the donor and acceptor traits and π-electron counts of the structural components. Herein, we report the synthesis and characterization of a series of A-D-A compounds consisting of BF₂ formazanates as electron acceptors bridged by a variety of π-conjugated donors. The results, which are supported by density functional theory calculations, demonstrate rational control of optoelectronic properties and the ability to tune the corresponding band gaps. The narrowest band gaps (E_g^Opt = 1.38 eV and E_g^CV = 1.21 eV) were observed when BF₂ formazanates and benzodithiophene units were combined. This study provides significant insight into the band gap engineering of materials derived from BF₂ formazanates and will inform their future development as semiconductors for use in organic electronics.

Aggregation-induced emissions in the mesogenic BF2 complexes of aroylhydrazines

PL peak intensity of 1a-BF2 (n = 12) versus f_w of THF/H₂O in pure THF (f_w = 0) and THF/water with a specific f_w. The concentration is 10 μM and PL emission was excited at 376 nm. Photos were taken under UV illumination.

Strong-Induced CPL Emission Promoted from Achiral Conjugated Polymer-Containing Emissive Nematic Liquid Crystals (P-N*-LCs)

With the rapid development on 3D printing technology, more and more works have been devoted to 3D display. 3D display will really come true by using circularly polarized luminescence (CPL)-active materials with both high quantum yield and dissymmetry factor (g_em ) in organic light-emitting diode or liquid crystals (LCs). But so far most of these CPL materials cannot meet the real application requirement because of the low g_em values in the range of 10^-5 -10^-2 . In this paper, ternary chiral emissive LCs (P-N*-LCs) is designed by doping chiral binaphthyl-based enantiomers as chiral dopant (Guest 1) and achiral conjugated polymer as induced CPL emitter (Guest 2) into nematic liquid crystal (N-LCs) Host 5CB. Both Guest 1 and Guest 2 show excellent compatibility with Host 5CB. The obtained ternary P-N*-LCs can emit strong-induced CPL signal with g_em up to 1.12 and Ф_FL up to 66.1%. This work first develops a new strategy for the smart design of excellent CPL materials from versatile achiral conjugation fluorescence polymers.

Photoelectron spectra and electronic structure of boron diacetate formazanates

The electronic structure and cationic states of two 1,5-diphenylformazanes and two boron diacetate (B(OAc)₂) formazanates were modeled using the outer valence Green's function (OVGF) and density functional theory (DFT) methods. Comparison of data of the OVGF and ultraviolet photoelectron spectroscopy (UPS) methods made it possible to determine an effect of functional groups and complexing agents on energies of cationic states. Addition of NO₂-group at the γ-position of the chelate cycle causes stabilization of levels the five upper occupied molecular orbitals (MO) and destabilization of the bonding orbital π₃^Ph + π₃ level. The levels of MOs π₃^Ph-π₃ and n_- are stabilized due to influence of the complexing agent B(OAc)₂, with a difference in the shift of 0.67 eV. The ionization energies (I_n) changes for the π-orbitals of benzene rings are within the error of the OVGF method. Under methylation of phenyl groups, the differences between the calculated I_n, corresponding to the π-orbitals of aromatic substituents, are in good agreement with the experimental I_n shifts at transition from benzene to toluene. According to the OVGF method, in all the studied complexes the lowest unoccupied molecular orbital (LUMO) is localized mainly on the chelate cycle and has a strong acceptor character, which should contribute the low-lying charge-transfer electronic excitations. Moreover, an application of the DFT analog of the Koopmans' theorem with the BHHLYP and B2PLYP functionals made it possible to determine qualitatively a sequence of cationic states and energy intervals between them in the spectral range up to 10 eV. The DFT/wB97x/cc-pVTZ method data on the energy gap between the highest occupied molecular orbital (HOMO) and LUMO levels correlate with the OVGF/cc-pVTZ calculation results.

Cation effects on dynamics of ligand-benzylated formazanate boron and aluminium complexes

The dynamic processes present in ligand-benzylated formazanate boron and aluminium complexes are investigated using variable temperature NMR experiments and lineshape analyses. The observed difference in activation parameters for complexes containing either organic countercations (NBu4+) or alkali cations is rationalized on the basis of a different degree of ion-pairing in the ground state, and the data are in all cases consistent with a mechanism that involves pyramidal inversion at the nitrogens in the heterocyclic ring rather than homolytic N-C(benzyl) bond cleavage.

Formazanate coordination compounds: synthesis, reactivity, and applications

Inorganic complexes of an emerging class of chelating N-donor ligands, formazanates, offer a unique combination of structurally tunable coordination modes, redox activity, and optoelectronic properties.

Boron difluoride formazanates with thiophene and 3,4-ethylenedioxythiophene capping and their electrochemical polymerization

BF₂ formazanates with thiophene and 3,4-ethylenedioxythiophene capping, prospective candidates for ambipolar semiconductors, have been synthesized and polymerized electrochemically.

Synthesis of fully-fused bisboron azomethine complexes and their conjugated polymers with solid-state near-infrared emission

We describe herein a robust π-conjugated molecules with solid-state emission in the near-infrared (NIR) region (Φ_F = 0.03–0.06).

Altering the optoelectronic properties of boron difluoride formazanate dyes via conjugation with platinum(ii)-acetylides

The absorption, emission, and electrochemical properties of conjugates of boron difluoride formazanate dyes and Pt(ii)-acetylides are systematically studied.

Structure and bonding in reduced boron and aluminium complexes with formazanate ligands

A comparison of structure and bonding in reduced formazanate B/Al complexes and their ligand-benzylated products is described. The kinetics of homolytic N–C(benzyl) bond cleavage in the latter compounds is studied.

Doping-free circularly polarized electroluminescence of AIE-active chiral binaphthyl-based polymers

AIE-active chiral polymer enantiomers (S-/R-P) can emit green circularly polarized electroluminescence (CP-EL) with g_EL up to 0.024.