Structure and electronic properties of alkylthiophenes coupled by Head-to-Tail and Head-to-Head regioselectivity

Abstract

No presente artigo, métodos teóricos foram utilizados na análise da estrutura e propriedades eletrônicas de oligômeros de alquiltiofenos considerando diferentes regiosseletividades. A lacuna de energia entre as bandas de valência e condução foi calculada nos níveis ab initio Hartree-Fock (HF) e teoria do funcional de densidade (DFT) e semi-empírico ZINDO/S-CI. Os resultados mostraram que o isômero Head-Head-Tail-Tail (HH-TT) apresenta menores valores para a lacuna de energia quando oligômeros com mais de três unidades monoméricas são considerados e que a substituição do anel tiofeno por grupos alquila não afeta significativamente a lacuna de energia. Esse resultado é importante no sentido que mostra que polímeros mais processáveis podem ser obtidos através da alquilação sem perda considerável de suas características condutoras.In the present paper a theoretical analysis of alkylthiophenes with Head-Tail-Head-Tail (HT-HT) and Head-Head-Tail-Tail (HH-TT) regioselectivities up to 6 monomeric units was carried out. Structure and electronic properties for the syn and anti forms were calculated by ab initio HartreeFock (HF) and Density Functional Theory (DFT) approaches. The energy gap between the conduction and valence bands was obtained at HF and DFT levels and also calculated with the semiempirical ZINDO/S-CI method. The results showed that the isomer with HH-TT regioselectivity presents lower energy gap for longer oligomers and the substitution of thiophene by alkyl groups does not change significantly the energy gap. This is important in the sense that more processable polymers can be obtained through alkylation without decrease the energy gap that is a molecular properties related to the electronic conductivity. Regarding to the conformational equilibrium, the syn form was found to be stable only for the HT-HT isomer and in this case the energy gap was found to be lower than those calculated for the anti form.

Thin Films of Highly Planar Semiconductor Polymers Exhibiting Band-like Transport at Room Temperature

“…For comparison, a benchmark polythiophene, regioregular poly(3-hexylthiophene) (rr-P3HT), exhibits a torsional angle of ∼70°o ver four subunits of thiophene rings. 13,14 The intense molecular interaction of the as-designed polymers could be confirmed phenomenologically from their strong tendency to form aggregates when dispersed in conventional organic solvents. For example, the photographs in Figure 1b demonstrate the evolution of P8T2Z-C12 dispersed in chloroform (1.0 wt %).…”

Structural and electronic properties of 4H-cyclopenta[2,1-b,3;4-b′]dithiophene S-oxide (BTO) derivatives with an S, S=O, O, SiH2, or BH2 bridge: semi-empirical and DFT study

“…The geometries of the [2,2′]dithiopene S-oxide (2TO) and bridged dithiophene S-oxide (BTO) derivatives were fully optimized using semi-empirical methods (AM1 and PM3), ab initio calculations (Hartree-Fock), and density functional theory (Beckes's three-parameter hybrid [28] functional) employing the Lee, Yang and Parr correlation functional B3LYP [29]). The basis set 6-31 G* was used for all atoms in the ab initio methods; this set has already been used by several researchers studying polythiophenes [24,25,[30][31][32][33][34]. The absorption transitions were calculated from the optimized geometry in the ground state S 0 using timedependent DFT (TD-DFT) theory [35,36].…”

Estrutura e propriedades da difenil-4-amina sulfonato de sódio: um dopante de filmes condutores

“…No nível DFT, estes valores podem ser estimados diretamente a partir das equações de Kohn-Sham, contudo a precisão das propriedades previstas depende fortemente dos funcionais de troca e de correlação usados 36 . Deve-se ressaltar que De Oliveira e colaboradores 37,38 , utilizando o método ZINDO/S-CI para calcular separação de energia entre as bandas de valência e condução dos polímeros alquiltiofeno 37 e cianotiofeno 38 , obtiveram boa concordância com os dados experimentais. Uma vez que a DASNa não pode ser calculada com o método ZINDO/S-CI, pois o programa não dispõe de parâmetros para o áto-mo de sódio, nos restringimos a um cálculo HF/6-31G*.…”