Nitrogen-Containing Analog of Dibenzoylmethanate of Boron Difluoride: Luminescence, Structure, Quantum Chemical Modeling, and Delay Fluorescence

Abstract

Boron difluoride of 3-amino-1,3-diphenyl-2-propene-1-onate (1) has been synthesized and its crystal structure has been determined. The comparative studies of 1 and its oxygen analog 1,3-diphenyl-1,3-dionate (dibenzoylmethanate) of boron difluoride (2) have been performed using the methods of stationary and time-resolved spectroscopy and quantum chemical modeling. It was established that at the transition from solutions to crystals, a bathochromic shift of the spectra and a significant increase of luminescence intensity of 1 take place. The luminescent properties of solutions of 1 and 2 are similar. The peculiarities of crystal packings of 1 and 2 are responsible for differences in crystals luminescent properties. For crystals of 2, one observes the luminescence of J-aggregates and excimers, while for 1, in which a dimer is an elementary structural fragment, only the excimer luminescence is registered. A delayed excimer fluorescence of the P-type was observed for crystals of 1 and 2 at room temperature. The intensity of the delayed fluorescence of 1 is 300-fold higher than that of 2. Graphical Abstract Luminescence of J-aggregates and the formation of excimers in crystals of 1 and 2.

Design, Synthesis, and Crystallization‐Induced Emission of Boron Difluorides β‐Ketoiminates

“…Previously we synthesized boron difluoride β‐ketoiminates and studied their luminescence properties . To reveal the relationship between the luminescence properties and the features of the molecular structure of boron difluoride β‐ketoiminates, the range of ligands was extended significantly.…”

“…Disorder of the quasi‐aromaticity is observed for nitrogen‐containing analogues of boron difluoride dibenzoylmethanate as well . These data allow us to conclude that there is a diene structure in the chelate cycle of boron difluoride β‐ketoiminates …”

“…The excimer formation requires the presence of pre‐excimer sites that comprise parallel molecules with a substantial degree of overlap . The optimal conditions for excimer formation would involve the existence of pairs of molecules with a sufficiently high degree of overlap and subsequent formation of J‐aggregates from the molecule pairs that comprise excimer traps …”

“…The group of boron difluoride ketoiminates that has been studied is rather limited: Mostly the luminescence properties of the compounds that contain bulky substituents by the nitrogen atom (phenyl, tert ‐butyl, p ‐bromphenyl, and p ‐methoxyphenyl) have been described . At the same time, it has been shown by way of example with boron difluoride enaminedibenzoylmethanates that small substitutions to the nitrogen atom considerably change the molecular structure and luminescence properties relative to β‐diketonate analogues . Boron difluoride ketoiminates are an important class of organoboron dyes because they possess prominent optical properties such as large molar absorption coefficients and high fluorescence quantum yields in the solid state .…”

J-Aggregates of Boron Difluoride β-Diketonates in Polymer Matrix: Formation and Dissociation. Temperature-Dependent Luminescence.

“…For example, di uoroboron β-diketonates exhibit mechanochromic properties [30][31][32] Earlier [33,34], it was shown that the luminescence of concentrated solutions of β-diketonates of boron di uoride was determined by the formation of brightly luminescent aggregates. Here, the low solubility of β-diketonates of boron di uoride with bulky substituents in organic solvents and, as a result, the low concentration of aggregates in solutions leads to the fact that, in most cases no changes are observed in an absorption spectrum of saturated solutions [35][36][37]. Although the evolution of the excitation and luminescence spectra along with an increase of the solution concentration indicates the formation of aggregates in the solution [35][36][37].…”