Preparation Of D-A Conjugated Polymers Via Direct Arylation Polycondensation And Properties Investigation

Nowadays, Direct arylation polycondensation is considered to a new "green" synthetic method application in the synthesis of D-A type narrow band gap conjugated polymers. Compared with the traditional polymerization methods, the direct arylation polymerization has many advantages, such as fewer synthetic steps, less time, higher monomer purity, less harmful substances on human beings and the environment, etc. In order to deeply explore the synthesis of D-A type narrow band gap conjugated polymers via direct arylation polycondensation, this article attempts to do the following:1. Four fluorene-thiophene alternating conjugated polymers were prepared with different reaction conditions. The experimental results show that the reactivity decreases with increasing the chemical shift of active C-H bond in four thiophene derivatives. The results are consistent with electrophilic substitution mechanism. Four polymers are good fluorescent material, which is proven by ultraviolet-visible absorption spectra and fluorescence spectrum. Fluorescence quantum efficiency testing found that fluorescence quantum efficiency of P1 was as high as 84.9%.2. D-A1-D-A2 new type narrow band gap conjugated polymers P5 was prepared with different reaction conditions. Polymer P6 and P7 were prepared with the optimum reaction conditions for synthesis of P5. Three polymers have common characteristics that DPP as"A1 "unit and BT as" A2 "unit. Three polymers have high thermal stability by TGA analysis. Three polymers have wide absorption, and the limit values expand to infrared region by ultraviolet-visible absorption spectra. The HOMO and LUMO energy levels of three polymers were calculated by electrochemical analysis. Three polymers are suitable for application in polymer solar cells by matching energy level with PC70BM. The computational analysis of three polymers by density functional theory (DFT) show that the coplanarity of order is P6>P7>P5. XRD data show that three polymers have smaller π-π stacking and stronger crystallinity.3. Polymer P8-P10 were prepared with the optimum reaction conditions for synthesis of P5. The structure characteristics of three polymers is what DPP as "A1 " unit and other electron-deficient unit as "A2" unit. Compared with P9, P8 and P10 have higher thermal stability by TGA analysis. Three polymers have wide absorption, and the limit values expand to infrared region by ultraviolet-visible absorption spectra. The HOMO and LUMO energy levels of three polymers were calculated by electrochemical analysis. Three polymers are also suitable for application in polymer solar cells by matching energy level with PC70BM. The simulation calculation show that three polymers have good coplanarity, and the coplanarity improved by the introduction of fluorine atom on polymer backbones.4. The polymer solar cells were prepared using polymer P5 as donor material and PC70BM as acceptor material. We used different methods to optimize the active layer morphology, and obtained the highest device efficiency of 3.65%. AFM images show that the device efficiency increases with the increasing of molecular weight. Besides, The solar cell based polymers P6-P10 were prepared with optimized conditions of P5, and device efficiency were 3.09%,0.32%,1.49%,0.31% and 0.03%, respectively.