Crystal structure and luminescence of 2,2-difluoro-4,6-(4-methylphenyl)-1,3,2-dioxaborine

Abstract

The crystal structure, luminescence properties of 2,2-difluoro-4,6-(4-methylphenyl)-1,3,2-dioxaborine (СH 3 C 6 H 4 COCHCOC 6 H 4 CH 3 BF 2 ) crystals and solutions at different concentrations are examined at T 296 K and 156 K.Keywords: boron difluoride β-diketonate, 2,2-difluoro-4,6-(4-methylphenyl)-1,3,2-dioxaborine, crystal structure, luminescence, H and J aggregates, quantum chemical simulation.Boron difluoride β-diketonates exhibit strong luminescence in both solutions and the crystalline state [1]. These compounds are employed in molecular electronics for they possess nonlinear optical properties [2], two-photon absorption [3,4], and photoconductivity [5].2,2-Difluoro-4,6-(4-methylphenyl)-1,3,2-dioxaborine (СH 3 C 6 H 4 COCHCOC 6 H 4 CH 3 BF 2 ) (1) belongs to boron difluoride dibenzoylmethanates bearing substituents in the phenyl rings. We have previously studied the spectral luminescent properties of solid boron difluoride dibenzoylmethanate (C 6 H 5 COCHCOC 6 H 5 BF 2 ) and its solutions [6]. The introduction of a methyl substituent, as exemplified by boron difluoride benzoylacetonate [7], strongly influences the supramolecular structure of the crystal, its luminescence properties being significantly affected. This contribution reports the effect of the crystal structure of 1 on its spectral luminescence properties as well as the evolution of spectral properties with an increase in the solution concentration. EXPERIMENTALCompound 1 was prepared by acylation of toluene with mixed anhydride of trifluoroacetic and malonic acids [8] (Scheme 1). X-ray quality crystals of 1 were obtained by recrystallization from toluene on slow cooling of the solution.Luminescence spectra of the crystals were recorded on a SDL-1 spectrometer (LOMO) at 300 K and 77 K, excitation source DRSh-250 lamp, UFS-6 filter (λ ex = 365 nm); excitation spectra and luminescence spectra of the solutions and crystals at 300 K were measured on a Shimadzu-RF5301 spectrofluorophotometer. Time-resolved luminescence spectra were recorded on a FluoTime 200 spectrometer (PicoQuant). A crystal with the dimensions of 10×1.35×0.6 mm was used for the time-resolved spectroscopic examination of compound 1. Complete X-ray structural investigation was carried out with a SMART-1000 CCD diffractometer (Bruker) at temperatures of 296(2) K and 156(2) K. Data collection for the crystal was carried out by ω-scanning in three sets of 906

New Fluorescence Domain “Excited Multimer” Formed upon Photoexcitation of Continuously Stacked Diaroylmethanatoboron Difluoride Molecules with Fused π‐Orbitals in Crystals

“…As ar esult,m olecules in these crystals are stacked in am anner that does not allow intermolecular overlap of the parent units corresponding to P1 BF 2 ,b ut enables stacking of the nBu or nPr alkyl chain and benzene moiety ( Figure 1, No overlap). The D C values for 1cBF 2 , 1dBF 2 , [34] and 1eBF 2 ,w hich contain less bulky substituents, are smaller than those for 1aBF 2 and 1bBF 2 ( Table 1, D C = 9.67 f or 1cBF 2 ,6 .80 for 1dBF 2 ,a nd 8.63 f or 1eBF 2 ). As ar esult,a djacent molecules in crystalso f Figure 1.…”

“…The observation that crystals of 1a-gBF 2 have longer l FL,C than l FL,S observed for CH 2 Cl 2 solutions of these substances is probably ac onsequence of J-aggregation. [1,2,34] The l FL,C of 1c-eBF 2 are longer than those of 1a-bBF 2 by approximately2 0-70 nm (Figure 3a andT able 2). Although the l FL,C of 1f-gBF 2 are also longert han those of 1a-bBF 2 ,t he differences between them are less than 20 nm, suggesting that the crystalsof1f-gBF 2 resemble those of 1a-bBF 2 in l FL .H owever,t he t FL,C of 1f-gBF 2 are more than three times as long as those of 1a-bBF 2 .…”

“…Among the substancesi nt his family,d ibenzoylmethanatoborond ifluoride (P1 BF 2 ,S cheme 1) is an especially interesting compound from the viewpoint of probing relationshipsb etween aggregation mode and FL properties. [23][24][25][26][27][28][29][30][31][32][33][34][35] Since the report by Mirochnik and co-workers showing that P1 BF 2 FL involves emission from arrays of molecules in crystalsi nw hich intermolecularo rbital interactions occur, [30][31][32][33][34][35] many others have observed that P1 BF 2 derivatives exhibit interesting molecular aggregation-based emissionp henomena such as mechanofluorochromism, [36][37][38][39] aggregation-induced emission (AIE), [40] and room-temperature phosphorescence. [41,42] Guided by thesee arlier efforts, we carriedo ut an investigation aimed at elucidating the FL properties and crystal-packing structures of 1BF 2 derivatives.…”

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

“…It is well known that the luminescence of boron difluoride β‐diketonates is excimer type, and the bathochromic shift of the luminescence spectra maxima upon transitioning from dilute solutions (monomeric luminescence) to crystals was able to reach 100 nm . In the excitation spectra of boron difluoride β‐diketonates, one can observe a narrow band of excitation of J‐aggregates .…”

Remarkable Solvatofluorochromism of a [2.2]Paracyclophane‐Containing Organoboron Complex: A Large Stokes Shift Promoted by Excited State Intramolecular Charge Transfer

“…The emissive properties of organoboron complexes,e specially dibenzoylmethanatoboron difluoride (1BF 2 ; Scheme1), have been the subjecto fs everals tudies.T hese substances have potential applications as emitting materials because they have some important advantageous features including easeo fp reparation and FL emissiono ccurring not only in solution but also in the crystalline state. [17][18][19] Furthermore, 1BF 2 containst wo benzene rings that serve as electrondonor moieties and a1 ,2-dihydro-2,6-dioxaborinine ring that acts as an acceptor moiety, [20][21][22] forming aD -A-D triad. The two Fatoms in 1BF 2 enhance the electron-accepting ability of the dihydrodioxaborinine ring and, as ar esult, are responsible for its efficient light-emission properties.…”