Synthesis And Photoelectric Properties Of The Derivatives Of Cyclopentadithiophenes

The derivatives of cyclopentadithiophenes have potential applications in organic field effect transistors,organic solar cells, conducting polymers, and organic light emitting diodes due to their special optical andelectrical properties. In this thesis, some new compounds based on cyclopentadithiophene were synthesized.Their optical and electrical properties were studied. The main work of this thesis can be separated into fourparts as following:1. Dicyanomethylene-cyclopentadithiophene compounds:7-dicyanomethylene-cyclopenta[1,2-b:4,3-b’]dithiophene (12, yield:96%),2,5-diphenyl-cyclopenta[1,2-b:4,3-b’]dithiophen-7-ylidenemalononitrile (13,yield:96%),4-dicyanomethylene-cyclopenta[2,1-b:3,4-b’]dithiophene (26, yield:96.7%),2,6-diphenyl-cyclopenta[2,1-b:3,4-b’]dithiophen-4-ylidenemalononitrile (28, yield:96.8%),7-dicyanomethylene-cyclopenta[1,2-c:3,4-c’]dithiophene (37, yield:97.1%), and3,4-diphenyl-cyclopenta[1,2-c:3,4-c’]dithiophen-7-ylidenemalononitrile (38, yield:95.4%) were successfully synthesized via Knoevenagelreaction. These compounds were characterized by NMR, mass spectrometry (MS), high-resolution massspectrometry (HRMS) and Fourier-transform infrared (FTIR). In the crystals of3,4-diphenyl-cyclopenta[1,2-c:3,4-c’]dithiophen-7-one (36) and38, the phenyl groups are deviating fromthe cyclopentadithiophene plane.2. Dicyclopentadithiophene compounds: tetrakis(2’-hexyl)-Δ7,7′-dicyclopenta[1,2-b:4,3-b’]dithiophene(16, yield:71%), tetrakis(2’-trimethylsilyl)-Δ7,7′-dicyclopenta [1,2-b:4,3-b’]dithiophene(15, yield:78%),tetrakis (2’-trimethylsilyl)-Δ4,4′-dicyclopenta [2,1-b:3,4-b’]dithiophene(30, yield:92%), Δ4,4′-dicyclopenta[2,1-b:3,4-b’]dithiophene(29, yield:89%), tetrakis(2’-phenyl)-Δ4,4′-dicyclopenta [2,1-b:3,4-b’]dithiophene(31, sublimated yield:30%), Δ7,7′-dicyclopenta [1,2-c:3,4-c’]dithiophene(39, yield:89%),tetrakis(3’-phenyl)-Δ7,7′-dicyclopenta [1,2-c:3,4-c’]dithiophene(40, yield:95%) were successfullysynthesized through McMurry reaction. The crystal structures of compound16,29, and39were studied. Itpresents a quasi-planar structure for compound16, and there exists a dihedral angle between the twocyclopentadithiophene planes in the crystal structure of compound29and compound39.3. Absorption spectra of these three series compounds (t-CDT, b-CDT, and s-CDT) were studied from two aspects of the position of S atom and the end-capped groups.1) For the position of S atom, the derivatives of t-CDT and b-CDT have a very weak absorption peakin the long wavelength region, compared with that of the derivatives of s-CDT. This phenomenon may becaused by the interaction between the substitutions and the molecular conjugated bone. Furthermore, theabsorption peaks of t-CDT and b-CDT derivatives have a red-shifting.2) For the end-capped groups, compared to the absorption of cyclopentadithiophenones (O-s-CDT,O-t-CDT, and O-b-CDT), intramolecular charge transfer absorption bands was observed at the wavelengthrange of300nm-400nm for the derivatives of substituting carbonyl with dicyanomethylene groups(CN-s-CDT, CN-t-CDT, and CN-b-CDT), and the absorption peaks of the derivatives with diphenyl groupsintroducing (DP-O-s-CDT, DP-O-t-CDT, and DP-O-b-CDT) have a significant red-shifting, and theabsorption peaks not only become broader and but also have a significant red-shifting with simultaneousintroducing of diphenyl groups and substituting carbonyl with dicyanomethylene groups.4. OTFTs based on these compounds were fabricated. The hole mobility of4.2×10-5cm2/Vs (Tsub=25oC) and3.0×10-5cm2/Vs (Tosub=70C) were obtained for compound31.