The Synthesis Of Novel Dendrimers And D-A Compounds Based On1,1,2,2-tetra (thiophen-2-yl)ethene

Thieophene-based dendrimers are a family of monodisperse polymers with well-defined thiopheneunits and three-dimensional geometry. The syntheses of thieophene-based dendrimers and their potentialapplications as functional materials have attracted more and more scholars’ attention. But, most of thesedendrimers were synthesized with the dendron of2,2’:3’,2’’-terthiophene or methyltri(thiophen-2-yl)silane.In this thesis, two novel thiophene-based dendrimers and two types of novel D-A compounds wereconstructed with the1,1,2,2-tetra(thiophen-2-yl)ethene. The main work of this thesis can be separated intotwo parts as following:Part1. Syntheses of two novel thiophene-based dendrimers using1,1,2,2-tetra(thiophen-2-yl)ethene1,1,2,2-tetra(thiophen-2-yl) ethene has good π-conjugation, four active sites and no cis-trans isomerscomparing with most vinyl type compounds. According to these characteristics, in this parttetrakis(thiophen-2-yl)ethene were utilized as the building block, via Suzuki and McMurry reactions, twonew dendritic thiophene-based compounds were synthesized. These two new dendrimers are the tetramerand pentamer of tetrakis(thiophen-2-yl)ethene, which contain16and20thiophene, respectively. The Br/Liexchange on2-bromo-5-trimethylsilyl thiophene were set in the presence of n-BuLi andN,N-dimethylcarbamyl chloride (DMC) was added into the reaction mixture to affordbis(5-(trimethylsilyl)thiophen-2-yl)methanone (2). The intermolecular McMurry reaction of2wasemployed to generate the modular building block, tetrakis(5-(trimethylsilyl)-thiophene-2-yl) ethene (3).N-bromo-succinimide (NBS) was used for monobromination of compound3, and the compound4wassuccessfully obtained in good yield. The prepared4is the key intermediate for the synthesis of dendrimer8and9. On the one hand, after the Br/Li exchange of4with n-BuLi, the corresponding monolithium,4-Liwas quenched with DMC to afford ketone6. Then, the novel thiophene-based dendrimer8was efficientlyobtained by intermolecular McMurry reaction of6under condition of TiCl4-Zn powder-pyridine in dryTHF. On the other hand, dendron5could be generated from4and2-thiopheneboronic acid via Suzukireaction. The deprotonation of5was performed using n-BuLi, and the monolithiated intermediate,5-Liwas subsequently treated with DMC to afford another ketone7. The other thiophene-based dendrimer (9) was also efficiently prepared efficiently using the similar reaction condition of compound8. In summary,with2-bromo-5-trimethylsilyl thiophene as starting material, the overall yields for8and9could beobtained in ca.28.3%and ca.24.9%isolated yields, respectively.Both the crystal structures of3and8are confirmed by single-crystal X-ray crystallography.3belongsto monoclinic, space group P2(1)/n and8belongs to triclinic, space group P-1. In3, the four C-C bondslinked to the cored double bond are almost planar. However, the four thiophene rings and the coredethylene are not planar. There are five interplanar angles of two thiophenes connecting to the three types ofC=C double bonds in8. All of these interplanar angles all are greater than54o, which indicate the highrepulsion and poor conjugation among8. Due to the high repulsion among the thiophene rings in8, itsabsorption peaks (370and388nm) are similar to that of3(369and388nm). However, that the integratedabsorbance in8is approximately fourfold that of3and an additional shoulder peak at500nm is clearlyobserved further proved the viewpoint above.Part2. Syntheses of two types of novel D-A compounds based on1,1,2,2-tetra(thiophen-2-yl)ethene and naphtho[1,2-b:4,3-b’:5,6-b’’:8,7-b’’’]tetrathiophene1,1,2,2-tetra(thiophen-2-yl)ethene is good electron donor, and the tetrathienonaphthalene has betterplanarity, which can be prepared via photoirradiation of tetrakis (thiophen-2-yl)ethene. In this sectiontetrakis(thiophen-2-yl)ethane and tetrathienonaphthalene were utilized as the building blocks to synthesizetwo new dendritic D-A compounds with propylene cyanide as the electron receptor through Suzukicoupling and Knoevenagel condensation. Using Katz improved condition, another modular building block12can be synthesized via the oxidative photocyclization of compound4. On the one hand, after the Br/Liexchange of12with n-BuLi, the corresponding monolithium,12-Li was quenched with DMC to affordketone13. On the other hand, the dendron15could be generated from12and2-thiopheneboronic acid viaSuzuki reaction. The deprotonation of15was performed using n-BuLi, and the monolithiated intermediate,15-Li was subsequently treated with DMC to afford another ketone16. Four novel D-A compounds10、11、14and17could be generated from6、8、13、16and malononitrile via Knoevenagel condensation,respectively.From the UV-vis absorption data, slight bathochromic shifts (50nm or so) could be observed for theD-A compounds with introduction the unit of thiophene bridge, which increased the conjugated length. When compared with tetrakis(thiophen-2-yl)ethane compounds10and11, the tetrathienonaphthalenecompounds14and17gave higher integrated absorbance, but the absorption curves of14and17were blueshifted about50nm, which indicated that the basic unit of the planarity increased, while the torsion anglebetween the branches increased, too.