Study On Synthesis And Photophysical Properties For A Novel Type Of BF₂Complexes And Their Ligands

BF2complexes have become important small organic fluorescence compounds and are widely applied since they have high fluorescence intensity, good heat stablity, high absorptivity, great quantum yields and their easily changed function groups. This paper is based on3-(2-Oxo-2-phenyl-ethylidene)-3,4-dihydro-lH-quinoxalin-2-one, kind of N,O double-dentates BF2complexes with β-enol-imine groups. We studied the relationships between structure and nature, effects of the substitute after chelating, and conclusions are as follow:1.Herein we describe the synthesis along with the property and the calculation study on a series of novel BF2complexes with N,O-bidentate ligands. These complexes are ready to be prepared in good yields by simple operation and exhibit intense fluorescence in solutions with multiple colors. A qualitative structureeproperty correlation has been established via the detailed measurements and verified by the DFT calculations. It is revealed that:(i) the dramatically blue-shifted spectral bands along with the substantially decreased molar extinction coefficient occur if a benzoyl is substituted by a carbethoxy on a complex;(ii) the amide moiety makes a large contribution for the long-wavelength fluorescence of complexes, but the substituent on the amide moiety is barely helpful for the extension of the p-conjugation;(iii) a complex with an electron-donating group at the quinoxalinone moiety has the larger red shifts of spectral bands and the less stability toward oxidation than the one with an electron-donating group at the benzoyl moiety;(iv) the increase of the HOMO levels may account for the long-wavelength emission while the short-wavelength fluorescence may be caused by the enhancement of the LUMO levels;(v) these BF2chelates have the solvent-independent photophysical performance due to the minute change of the dipole moments between the SO and the S1state. Moreover, the electrochemical investigation shows that thesenovel N,O-bidentate BF2chelates are better electron acceptors than the commonly used electron-transport material Alq3. The further research on exploiting them as electron-transporting materials is on the progress.2.Herein we report the synthesis of a novel compound2,3-diphenylfuro[3,2-b]quinoxaline and the research on its photophysical and electrochemical properties. The X-ray crystallograph yindicates that the unique "herring-bone" arrangement of the isolated dimers, by which the network of the π-π stacking can be dramatically inhibited, is the main reason for the intense solid-state fluorescence. An assumed ICT transition accounting for the solvent-reliant emission is confirmed by the TD-DFT calculations. Additionally, the theoretical simulation reveals that the geometric relaxation from the SO to the S1state should be responsible for the large Stokes shift. Moreover, the low LUMO level and the long radiative lifetime make this compound as a promising material in fields involving OLEDs, fluorescence imaging, and so on.3.Although there is a great deal of reports on various AIE compounds, few works on those with the ESIPT aspect are presented. Herein, we describe the synthesis, characterization and photophysical properties of a novel family with the significant AIE activity. Each of them can readily go through an ESIPT reaction followed by a TICT-caused fluorescence quenching in solvents. However, it is verified that only the ESIPT reaction rather than the TICT process can be smoothly carried out in the aggregated state. The restriction of the torsion between the quinoxalinone and the dihydroquinoline fragment via the C4-C5bond in the Si state should predominantly account for the AIE phenomenon in this system. Compared with the other common AIE-active molecules with short-wavelength emission, our compounds exhibit the intensely red fluorescence which is much helpful for the bioanalysis of living specimens. The simple preparation procedure and the ready availability of the starting substrates make our AIE-active molecules quite easily accessible. The application of them in bioanalysis by the further modification is under the study.