Synthesis And Properties Of Ketocoumarin Fluorescent Compounds

As an important functional material, ketocoumarin compounds afford large molarextinction coefficient, high fluorescence quantum yield, good stability, wide tunablerange of maximum absorptions as well as easy synthesis. These compounds haveexhibited promising potential in many fields such as fluorescent dyes, solar cells,photosensitive agents, organic two-photon absorbing materials and nonlinear opticalmaterials. In this project, eleven novel D-Ï€-A type and five A-Ï€-D type ketocoumarincompounds were synthesized and characterized using FT-IR,~1H NMR and MS. Thestructure of3-acetyl-8-methoxy coumarin was further confirmed by X-ray singlecrystal diffraction.The relationship between the structures of the novel coumarin and their opticalproperties were studied to show that the corresponding maximum absorption of3-acetyl-coumarin compounds shift from299~434nm to332~502nm. Meanwhile,due to the enhanced conjugacy effect and aryl vinyl ketone structure unit, thefluorescence quantum yield was improved from0.032~0.086to0.55~0.95. Theintroduction of electron-donor group at7-position brings greater impact on thespectral properties of coumarin compounds than at4(or6,8)-positions, resulting inhighest red shift of the maximum absorption and emission wavelength, as well assignificant enhancement of fluorescence quantum yield. The ketocoumarin compound3b bearing sensitizer structure exhibits strong absorption in visible region (400to600nm) and the electrochemical study verified that its redox potential at ground andexcited state can meet the requirements for photosensitive dyes in DSSC. Thephotoelectric conversion efficiency of the DSSC with3b as the sensitive dye wasfound to be1.79%.Density Functional Theory (DFT) and Time Dependent-Density FunctionalTheory (TD-DFT) were employed to theoretically calculate the geometricconfiguration, track layout, infrared spectroscopy,1H NMR and UV-visible absorptionspectra of the as-synthesized coumarin compounds. The calculation data were foundto be consistent with the experimental results. Furthermore, the study of molecularorbital layout demonstrates that their absorption spectrum originates from Ï€â†'Ï€* electronic transition from HOMO to LUMO type, that is effective intramolecularelectron transfer after the photoexcitation. The calculation results verify the rationalityof the structure design of all the synthesized coumarin compounds.