Reversible luminescence thermochromism of dibenzoyl(methanato)boron difluoride

Abstract

Reversible luminescence thermochromism of dibenzoyl(methanato)boron difluoride was found. A substantial hypsochromic shift of the luminescence band maximum (60 nm) with a temperature decrease from 300 to 77 K was observed, and the luminescence color changed from green to blue. A considerable decrease (by 0.386 Å) in the unit cell parameters along the c axis was detected by X ray diffractometry when the temperature of the crystal decreased from 293 to 123 K. Shortening of the distances between the planes of adjacent molecules (stacking factor) weakens the interaction between the dimers and enhances the monomeric and excimeric luminescence.Development and synthesis of reversible luminescent thermochromes are urgent from both practical and theo retical standpoints. 1,2 One of the promising lines of search for new luminescent thermochromes is a study of mo lecular organized organic systems, including dimers, tri mers, and aggregates of conjugated molecules, whose supramolecular architecture produces different intermo lecular interactions: dimeric (excimeric), interdimeric, and stacking interactions. 3,4Continuing our works on studying the interrelation of the structure and luminescence and photochemical prop erties of boron difluoride β diketonates, 5-7 in this work we studied a change in the luminescence of dibenzo yl(methanato)boron difluoride (1) at different tempera tures and revealed reversible luminescence thermo chromism of this compound, namely, a substantial hypso chromic shift of the fluorescence band maximum (60 nm) and a change in the luminescence color from green to blue when the temperature decreases from 300 to 77 K. ExperimentalCompound 1 was synthesized according to a previously pub lished procedure. 8 Crystals were prepared by recrystallization from an acetonitrile-toluene (1 : 1) mixture. Fluorescence spec tra of solutions were obtained on a Shimadzu RF 5000 in strument. Luminescence spectra of crystalline compounds at 77-300 K were recorded on an SDL 1 spectrometer, using a DRSh 250 lamp as an excitation source and an UFS 6 filter (λ exc = 365 nm). To measure a temperature dependence of the luminescence spectra, a sample was placed in a quartz Dewar flask above the liquid nitrogen surface. The temperature of the sample was measured by a platinum thermocouple. The X ray diffraction study of compound 1 was carried out at 293, 203, and 123 K in a SMART 1000 CCD Bruker system using Мо Кα radiation. Results and DiscussionAs can be seen from the data in Fig. 1, a decrease in the temperature of the crystal from 300 to 77 K produces a substantial hypsochromic shift of the fluorescence band maximum of compound 1 (60 nm). For a more detailed analysis of the evolution of the luminescence spectra with a temperature change, the spectra were deconvoluted by the Gaussian expansion using the Origin 6.1 program; the results of deconvolution are presented in Fig. 1.It turned out that the fluorescence spectrum of com pound 1 at each temperature consists of three compo nents with maxima at 470, 500, and 560 nm, and o...

Alkyl chain length effects on solid-state difluoroboron β-diketonate mechanochromic luminescence

“…1d and Table 1. Previously Mirochnik showed that C1 crystals display excimer fluorescence, 31 which is similar to C1 data here. With the exception of C2 which is considerably blue shifted relative to the powder, all other Cn SE films had nearly identical emission maxima to powder samples, with emission maxima blue shifting with increasing alkoxyl chain length.…”

“…For C1, the long lifetime (30.94 ns) and broad, structureless band have been attributed to excimer emission. 31 However, for C2-C18, much shorter lifetimes were observed (s pwo 32 ¼ 3-7 ns), suggesting different dye emissive species. Light reabsorption or light scattering associated with the bulk powder, [33][34][35] and aggregation effects (e.g.…”

Reversible luminescence thermochromism and phase transition in crystals of thiophenylacetylacetonatoboron difluoride

“…Unlike respective 1,3-dicarbonyl compounds, b-diketoboron difluorides shows an intensive luminescence both in solutions and in crystals [3]. This class of compounds is characterized by excimer luminescence observable as in solutions and as in crystals [4,5], moreover, luminescent thermochromism and size-dependent luminescence were observed in some crystals [6][7][8]. The optic properties of b-diketonatoboron difluorides crystals are closely connected with their molecular architecture [5,9].…”

Polymorphism and Reversible Mechanochromic Luminescence for Solid-State Difluoroboron Avobenzone

“…16 For example, many difluoroboron dibenzoylmethane (dbm) derivatives show bathochromic shifts of ∼100 nm with ∼50 nm band width broadening. 17 In contrast, all three BF 2 AVB solids show very narrow band width emission relative to fluorescence in CH 2 Cl 2 [λ em ) 433 nm; full width at half-maximum (fwhm) ) 47 nm]. Among them, the dendritic solid formed by rapid solvent evaporation shows the most narrow emission band (fwhm ) 31 nm), with peak intensity at λ max ) 459 nm.…”