The synthesis and optical investigation of novel benzimidazole type dyes designing for dye sensitized solar cells (DSSCs)

In this thesis, novel benzimidazole type dyes were synthesized and characterized for dye sentisized solar cell (DSSC) systems. In the design of dye molecules, D-?-A framework was taken as a basis and new model planning was provided according to the requirements.At present work, 4,7-dibromo-2,1,3-benzothiadiazole molecule was synthesized from 2,1,3-benzothiadiazole molecule which is brominated at 4- and 7- positions of the ring. Suzuki Coupling method was used by bonding both sides of the molecule in order to obtain different boronic acid derivatives, respectively, 4,7-bis(3-methoxyphenyl)-2,1,3-benzothiadiazole (2a), (3-{7-[3-(dimethylamino)phenyl]-2,1,3-benzothiadizole-4-yl}phenyl)dimethylamine (2b) and 3,3'-(2,1,3-benzothiadiazole-4,7-dyl)dianiline (2c) molecules. Photophysical properties were investigated by fluorescence spectrophotometer measuring the emissions and also electrochemical properties were determined with cyclic voltammetry. In the analysis of emission and absorption spectra, absorption maxima of 2a, 2b and 2c does not any shift in benzonitrile solvent. The absorption maxima of 2a in the different solvents of polarities show a shift towards the red region as the polarity of the solvent increases. When we investigate the emission spectra of 2a, 2b and 2c in benzonitrile solution, emission wavelengths of 2b and 2c shift blue region and the shape of the spectra was changed. Also, fluorescence quantum yield of 2a in benzonitrile is higher than that of 2b and 2c showing stronger electron-releasing behavior. This causes the fluorescence quenching and the fluorescence quantum yield decreases.The other molecules for DSSC systems were synthesized starting from the 2a and 2b molecules. Diamine derivatives were synthesized by reduction reaction with NaBH4. 4-[4,7-bis(3-metoksifenil)-1H-benzimidazol-2-il]benzaldehit (4a) and 4-{4,7-bis[3-(dimetilamino)fenil]-1H-benzimidazol-2-il}benzaldehit (4b) molecules were synthesized. 4a and 4b products react with cyano acetic acid in order to obtain the target products, (2E)-3-{4-[4,7-bis(3-methoxyphenyl)-1H-benzimidazole-2-yl]phenyl}-2-cyanoacrylic acid (5a) and (2E)-3-(4-{4,7-bis[3-(dimethyamino)phenyl]-1H-benzimidazole-2-ly}phenyl)-2-cyanoacrylic acid (5b). ?CN and -COOH groups are effective groups especially for solar photovoltaic applications. In particular, final products can bind firmly to TiO2 surface with the aid of the ?COOH groups binding effectively to TiO2 surface.Structures of all synthesized compounds have been identified by UV-Vis, FT-IR, 1H-NMR, 13C-NMR spectroscopic methods. Photophysical properties were investigated by fluorimeter measuring the emissions and also, electrochemical properties were determined with cyclic voltammetry. As regards cyclic voltammetry measurements, the HOMO-LUMO energy levels and the energy band ranges 5a and 5b products appears to be promising for DSSC technology.