Synthesis And Photoelectrochemical Property Studies Of Carbazole D-Ï€-A Type Organic Photosensitive Dyes

As development of society, human have been aware of the more and more serious energy crisis. Scientists are working to improve the utilization of clean and environmentally friendly solar energy. Solar cells are kinds of devices that convert solar energy into electrical energy. In the field of solar cells, dye-sensitized solar cells (DSSC) have been attracting many researchers’attention, because of their low cost and simple preparation. The core of organic DSSC is an organic photosensitive dye with a type of D-π-A structure; these dyes have many advantages compare with the metal complexes, such as diversity of molecular structures, easy designing and purification, lower cost, as well as high molar extinction coefficients.In this paper,N-alkyl carbazole-3-formaldehyde and N-alkyl carbazole-3,6-dicarbaldehyde as intermediates were synthesized by alkylation of the carbazole with alkyl halides and followed by formylation with dimethyl sulfoxide and phosphorusoxychloride, the total yields of the two-step reaction were62.1%～66.8%; N-alkyl carbazole-3-formaldehyde and N-alkyl carbazole-3,6-dicarbaldehyde were subjected to condensation with cyanoacetic acid or rhodanine3-acetic acid by Knoevenagel reaction, and four series of dyes were obtained.(1) Dyes with N-alkyl (ethyl, isopropyl, allyl,n-butyl,n-hexyl, and benzyl) carbazole as electron donor, cyanoacrylate as electron acceptor, referred to as CC1, in yields of67.7%～89.8%.(2) Dyes with N-alkyl (ethyl, isopropyl, allyl,n-butyl,n-hexyl, and benzyl) carbazole as electron donor, rhodanine-3-acetic acid as electron acceptor, referred to as CL1, in yields of90.2%～93.8%.(3) Dyes with N-alky (ethyl, allyl,n-butyl,n-hexyl, and benzyl) carbazole-3,6-dicarbaldehyde as electron donor, cyanoacrylate as electron acceptor, referred to as CC2, in yields of75.6%～80.5%.(4) Dyes with N-alky (ethyl, allyl,n-butyl, and n-hexyl) carbazole-3,6-dicarbaldehyde as electron donor, rhodanine-3-acetic acid as electron acceptor, referred to as CL2, in yields of79.8%-83.8%. Structural identifications of the target compounds and intermediates were made by modern analytical testing techniques such as IR and1H NMR, combined with their physical and chemical properties. Th UV-Visible absorption spectra and fluorescence emission spectra and cyclic voltammetric behaviour of the dyes were also measured. The studies show that all of the dyes have high molar extinction coefficients, CL1(3) has the highest molar extinction coefficients (19634M-1·cm-1) at438nm. All dyes with rhodanine-3-acetic acid as electron acceptor, show significant red shif relative to dyes with cyanoacrylate as electron acceptor, such as the maximum absorption wavelength (439nm) of dye CL1(1) show significant red shif relative to CC1(1)(388nm). Molecular structure has a great influence on the fluorescent properties of dyes, increasing of the conjugated system in the dye molecular structure is conducive to the generation of fluorescence, and also conducive to the peak redshift of fluorescence emission. In the case of the same N-substituent in carbazole ring, the largest fluorescence emission peaks of CL1and CL2show a redshift to nearly60nm than those of CC1and CC2. The test of cyclic voltammetry proved that the oxidation-reduction reaction of the synthetic dyes can occur under certain conditions.