β‐Iminoenamine‐BF₂ Complexes: Aggregation‐Induced Emission and Pronounced Effects of Aliphatic Rings on Radiationless Deactivation

Abstract

The synthesis, photophysical, and electrochemical attributes of a novel class of boron difluorides containing an aromatic-fused alicyclic/hetero-alicyclic ring built on a β-iminoenamine chromophoric backbone are reported. The compounds displayed large Stokes shifts (86-121 nm), and were emissive in the solid state. The quantum yields obtained in solution at room temperature were unusually lower by an order of magnitude compared to those in the solid state. Some of the tested compounds displayed aggregation-induced emission (AIE). Single crystal XRD analyses revealed a lack of interplanar π-π interactions, which are presumed to be absent owing to non-planarity of the alicyclic component in the molecule. For most of the studied compounds, time-dependent DFT (TD-DFT) calculations invariably reveal intramolecular charge transfer (π-π*) characteristics with the frontier orbitals concentrated on the boron-nitrogen heterocycle. The participation of boron and fluorine atoms was found to be negligible.

Recent progress of optical functional nanomaterials based on organoboron complexes with β-diketonate, ketoiminate and diiminate

“…[39][40][41][42] By grinding powder samples in the crystal state, materials typically convert into the amorphous state; the resulting molecular distribution would thus be randomized, and the degree of intermolecular interactions should be significantly different. As a result, changes in emission color or intensity can thus be observed.…”

Oxygen Sensing Difluoroboron Dinaphthoylmethane Polylactide

“…11,12 These fluorescent dyes use the difluoroboron (BF 2 ) unit to restrict intramolecular rotation and vibrational freedom of the β-diketonate ligand, producing bright and efficient fluorescence. 13,14 Various types of BF 2 fluorescent materials have been prepared, including β-diketiminate (NBN), 15,16 β-ketoiminate (NBO), 17–21 and β-diketonate (OBO) complexes. 22–24 Difluoroboron can also act as an electron-accepting group, inducing a strong dipole upon excitation, making the dyes sensitive to solvent and media polarity.…”

Metal‐Free Triplet Phosphors with High Emission Efficiency and High Tunability

“…[5b] A key factor to the successful realization of singlet fission based materials relies on the design of molecules with appropriate electronic structure requirements that enables judicious disposition of the ground state as well as the excited state. [11] This work purposedly combines the electronic and structural requirements favoring singlet fission by satisfying different criteria such as presence of strong dipole moments, p-p interactions (see Scheme 1) and appropriate functional groups such as an aromatic nitro group as a part of the conjugate unit that can to some extent exhibit radical character in the excited state. [10] Moreover, the chemical and the electronic versatility of the molecular scaffold amenable to suitable modifications allows for achieving superior photoluminescent behavior both in the solid state as well as in solution.…”