Study On The Synthesis And Crystal Structures Of Benzothiahelicenes

The synthesis and characterization of thiophene fusedπ-conjugated molecules and polymers are of current interest owing to their potential applications in organic optoelectronic materials and devices. The heterohelicenes with thiophene units fused in the polyaromatic rings show attactive molecular structures with aesthetics. The synthesis of such kind of benzothiahelicenes is very challenged and attracted to many organic chemists. In this dissertation, the efficient synthesis of several kind of benzothiahelicenes has been developed by using the photocylization and non-photochemical synthetic methodologies. The research work is composed of four parts:1. Syntheses and Crystal Structures of Benzohexathia[7]helicene1.1 Synthesis of 2, 11-Dioctylbenzohexathia[7]helicene (12) under Irradiation and its Crystal Structure12 could be prepared in four steps with dithieno[2,3-b:3',2'-d]thiophene (5) as starting material (Scheme 1).1) 5 was treated with LDA and quenching with 1-bromooctane to give 2-octyldithieno[2,3-b:3',2'-d]thiophene (6) in 33.8% yield. 2-octyldithieno[2,3-b:3',2'-d] thiophene-2-carbaldehyde (7) was made in 97.9% yield by using 6 treated with LDA and quenching with DMF. The McMurry reaction was employed in making 1,2-(5-octyldithieno-[2,3-b:3',2'-d]thiophen-2-yl)-ethene (11) in 94.9%. Finally, the photocyclization of 11 in the presence of iodine in dry benzene was empolyed in making 12 in 32.3% yield. The total yield of making 12 was 10.2% with 5 as starting material. Rac-12 crystallizes in monoclinic, space group P2(1)/n. In the crystal, the strongπ…S and S…S interactions between two enantiomers, (R)-12 and (S)-12 could be observed. 1.2 Synthesis of 2,11-Di(trimethylsilanyl)-benzohexathia[7]helicene (22) and its Crystal Structure5,5'-di(trimethylsilanyl)-3,3'-bis-dithieno[2,3-b:3',2'-d]thiophene (29) was treated with LDA and DMF to generate 5,5'-di(trimethylsilanyl)-3,3'-bis-dithieno[2,3-b:3',2'-d]-thiophene-2,2'-dialdehyde (30) in 92.6% yield. The intramolecular McMurry reaction was employed in making 2,11-di(trimethylsilanyl)-benzohexathia[7]helicene (22) in 42.4% yield. The total yield of making 22 was 39.3% with 29 as starting material (Scheme 2). Slow evaporation of solution of 1 in a mixture of solvents of CHCl3 and CH3OH (1:3, v/v), two kind of crystals of 1 were obtained at same time. One with slight pink belongs to orthorhombic Pbca space group and another one is colourless, shows triclinic P-1 space group. The S…S,π…S andπ…πinteractions are observed in both crystals between (R)-22 and (S)-22.2. Synthesis of Novel Naphthalene Cored Double Hexathia[7]helicene and its crystal structureThe efficient synthesis of highlyπ-extended naphthalene cored double helicence, 5,5',5",5'''-tetra(trimethylsilyl)-naphtho[1,2-b:3,4-b':5,6-b":7,8-b''']tetra(dithieno[2,3-b :3',2'-d]-thiophene) (34) was obtained in our work with dithieno[2,3-b:3',2'-d]-thiophene (DTT) as building block.29 was treated with LDA and DMC to afford an novel ten membered cyclic diketone, a dimer of bis(5-trimethylsilanyldithieno-[2,3-b;3',2'-d]thiophen-2-yl)-methanone (39). The intramolecular McMurry reaction of 39 was employed to obtain the naphthalene cored double helicene, rac-34 in 80.1% yield. The total yield of making 34 was 39.9% with 29 as starting material (Scheme 3).34 is a novel compound bearing four twist DTT arms with double helical structure. It crystallizes in the orthorhombic, P212121 space group.34 shows strong The S…S,π…S andπ…πinteractions between (R,R)-34 and (S,S)-34. In addition, the diketone,39 also shows somewhat of double-helix like conformation and crystallizes in triclinic, P-1 space group.3. Synthesis and Aggregation-Induced Emission Characteristics of 1,1,2,2-tetra (5-trimethylsilyl-dithieno[2,3-b:3',2'-d]thiophene-2-yl)-ethylene(36)1,1,2,2-Tetra(5-trimethylsilyl-dithieno[2,3-b:3',2'-d]thiophene-2-yl)-ethylene(36) was synthesized by using the 5-bromo-2-trimethylsilanyldithieno[2,3-b:3',2'-d]-thiophene (27) as the starting material. The total yield of making 36 was 16.7% with 27 as starting material.The fluorescence behaviors of 36 in H2O-THF binary solvent system and in thin film show that 36 is a kind of aggregation-induced emission (AIE)-active compound. It is clearly confirmed by solvent effect, temperature effect and viscosity effect that the restriction of intramolecular C-C bonds rotation plays a crucial role in the AIE process. Some interesting aggregation phenomena of 36 were observed. In H2O-THF binary solvent system,36 emits green light peaked at 500 nm with water fractions of 55-60%. When mediate temperature decreased to 77 k,36 emits yellow light peaked at 560 nm in ethyl ether. However, in glycerol-methanol binary solvent system with glycerol fractions of 30-90% at room temperature,36 emits orange light peaked at 595 nm. The different PL emissions are probably due to different aggregation state.4. Synthesis and Crystal Structure ofΔ7,7'-dicyclopenta[2,1-b:4,3-b']dithiophene (41)The total yield of making 41 was 50.9% with 3 as starting material. (TMS)4-41 crystallizes in monoclinic, C2/c space group. It is a planar molecule with high conjugation. The averagement of data of single bonds and double bonds in molecule (TMS)4-41 could be observed from its crystal data.