Synthesis, Performance And Theory Of The Novel ¦Â-enol Imine-type Organic Boron Difluoride Complex Computing Research

BF2complexes have become important small organic fluorescence compounds and arewidely applied since they have high fluorescence intensity, good heat stablity, highabsorptivity, great quantum yields and their easily changed function groups. This paper isbased on3-(2-Oxo-2-phenyl-ethylidene)-3,4-dihydro-¹H-quinoxalin-2-one, kind of N,Odouble-dentates BF2complexes with β-enol-imine groups. We studied the relationshipsbetween structure and nature, effects of the substitute after chelating, and conclusions are asfollow:(1) spectroscopy aspects: Great changes take place after chelating in IR,¹H NMR,¹³C NMRspectrograms. The most obvious changes in IR are the peaks of B-O bond's stretchingvibration between1100¹300cm-1; The H singnal in low field disappeared and thesingnals in¹H NMR spectrograms shift to low field. The most obvious changes in¹³CNMR spectrograms is the singnal of carbonyl carbon at180ppm shift to160ppm as aenol carbon after chelating. And changes in19F NMR spectrograms can be well matchedwith the changes of conjugate electron density resulting from the changes of substituteand position.(2) optical spectroscopy aspects: Signals show obvious red shift in UV spectrum. This isattributed to the enhance of coplanarity after chelating. And maximum absorptionwavelength and emission wavelength can be well matched with the changes ofconjugate electron density resulting from the changes of substitute and position, so dothe molar extinction coefficient and fluorescence quantum yields. Generally speaking,electron-donating groups and a better coplanarity lead to better optical properties. Whena small group such as methyl substitute is introduced, the vibration relaxation ofexcitation state will be enhanced and the fluorescence quantum yields decrease. Andthese compounds have little solvent effects.(3) electrochemistry aspects: We survey the CV curves of example compounds and getenergy of HOMO and LUMO. And it can be well matched with the changes ofconjugate electron density resulting from the changes of substitute and position. We compare the energy of HOMO and LUMO with theoretical calculation and found itmatched well.(4) theoretical calculation aspects: From theoretical calculation we know that little solventeffects of these compounds result from the little Dipole Moments changes betweenground state and excitation state. Compared to ligand, the shift of spectrum is totallybecause the decrease of LUMO energy of coordination compounds. The HOMOâ†'LUMO transition is the most important component part of Ï€â†'Ï€*transition. Besides,theoretical calculation matched well with characteristic vibration frequency, maximumabsorption wavelength and emission wavelength of experimental data. This help us havea preliminary understand of the luminous mechanism.