Selective Deprotonation Of Cycloocta[1,2-c:4,3-c':5,6-c'':8,7-c''']tetrathiophene And Its Thionic Substitution:Syntheses And Photoelectric Properties Of Annular Planar Oligothienoacene

As one of the aromatic polymers,oligothiophenes have attracted more attentions in the field of organic semiconductor materials.Cyclooctatetrathiophene(COTh)is a distinctive one of oligothiophenes.With a special and flexible "saddle-shaped" structure,COTh is regularly used to build oligothiophenes with diversified configurations.In these derivatization works,annular oligothienoacenes,which are generated from COTh.have been proved to possess potential applications in the field of photoelectric materials.However,the low synthetic yields and lack of effienct synthetic methods restrict the application of annular oligothienoacenes in organic chemistry and material science.In this dissertation,the mechanism of high selective deprotonation of cycloocta[1,2-c:4,3-c':5,6-c":8,7-c'"]tetrathiophene(COTh-1)was systematicly studied,and a series of annular oligothienoacenes were designed and synthesized.Preliminary photoelectrical properties were characterized.The main work of the dissertation can be divided into three parts as follows:I.The mechanism of selective deprotonation of COTh-1In the presence of BuLi,the process of the deprotonation of COTh-1 was controlled by the change of reaction temperature and time in THF solvent.Through evaluation of the distribution the final products,the deprotonation of COTh-1 was recognized to follow a stepwise lithiated procedure which could be divided into four step-wised proton-depriving from the skeleton of COTh-1.This stepwise deprotonation give two specific selectivities in different reaction stage:contralateral one and ipsilateral one for the dilithiation and tetralithiation of COTh-1,respectively.Origination of these two specific selectivities were studied through the quantum calculation and single crystal of dilithio-bithiophene,and the possible mechanism was proposed.It was manifested that the inductive effect caused by monolithiation of COTh-1 and the lithium bridges were dominant factors for the formation of contralateral and ipsilateral selectivities,respectively.Different from the specific selective cases of mono-lithiation and dilithiation of COTh-1,terlithiation of COTh-1 does not show such selectivity in the presence of 3 equivalents of BuLi at-78?.In addition,it is observed that tetralithium of COTh-1 shows good reactivity with electrophiles to form a wide interesting derivatives.?.The stepwise sulfur substituted cyclization of COTh-1Compound 2a was synthesized in a yield of 51%by the tetralithiation of COTh-1 and the following reaction with benzenesulfonic thioanhydride.Start from 2a,compound 4(sulflower)was obtained a yield of 60%through similar synthetic strategy.The four TMS substituted derivative 2b show specific selectivity in the deprotection reaction to obtain 2c.Based on this selectivity,3a was generated in 85%yield.It was concluded that the strategy of stepwise sulfur substituted cyclization of COTh-1 is a selective,an efficient and mild approach for the syntehses annular oligothienoacenes.Similar to 4,2a showed a planar configuration in the single crystal.The packing of molecule,2a showed more close arrangement and stronger?-?intermolecular interactions than 4 were observed.Introductions of sulfur bridge induced the planarizartion of COTh-1,and the degree of planarizartion is proportional to the number of introduced sulfur atoms.Electron density in the eight membered ring is also increased with the introduced sulfur atoms.Caused by the steric effects of the introduced TMS groups,2b,2c and 3b show distorted configurations.According to the tiny changes of the bond length of the eight membered rings of these compounds,no inductive effect was brought in belong with the introduced TMS groups.?.Photoelectrical properties of cyclic oligothienoacenesDMSO solution of 2a show 260 nm,273 nm and 284 nm absorption peaks in Uv-vis spectra.The peaks in 273 nm and 284 nm were disappeared in thin firm Uv-vis spectra of 2a.Both of the DMSO solution and thin firm of 3a and 4 expressed a unique absorption peaks(?=260 nm)between 260 nm and 300 nm.The thin firm optical bandgap of them could be verified in the values 3.90 eV(2a),3.70 eV(3a)and 3.82 eV(4).According to the optimum structure,it was found that,differnet from the plane structure of 2a in single crystal,distorted configurations was present in its molecular state.The transformation from distortion to plane might be caused by the intermolecular interactions in the process of molecular aggregation,and might be the reason to the disappearance of two absorption peaks at 273 and 284 nm of 2a in solution.Similar planar configurations were present in optimum structures of 3a and 4,and all the thiophene units were fused into a whole conjugated system.These structural characteristics cause the absence of absorption peaks around 270 nm in both DMSO solution and thin firm of 3a and 4.The cyclooctatetraene cores at the center of molecules of 2 to 4 were studied by the DFT calculation and showed antiaromaticity,and their antiaromatic degrees show raised tendency with the increase of molecular planaritis and electron densities.Electrochemistry properties of 2a and 3a were characterized by CV in solid thin films and show two and one irreversible redox peaks,respectively.EHOMO values of 2a is-5.55 eV,and 3a is-5.70 eV.Their OFET devices were prepared and show 7.5×10-4 cm2V-1s-1 and 2.6×10-3 cm2V-1s-1 carrier mobilityies,respectively.