Density functional theory was adopted to optimize the ground state geometries of α-oligothiophenes H(C4 H2S)nH (n = 2-13) with B3LYP and CAM-B3LYP methods of 6-31G (d) basis set .In the meantime ,the absorption spectra of H (C4 H2 S)n H were calculated with TD-B3LYP method ,and their analytic expressions of vertical transition energies versus size n werederivedtherewith .Moreover,theemissionspectraofH(C4H2S)nHwerecalculatedatthe TD-CAM-B3LYP level .Results indicate that H (C4 H2 S )n H have three kinds of ground state geometries :spiral-rising structure ,circular structure and slightly curvulate banded structure . The first two structures are cis and the last one is trans;the circular structure has C2 symme-try ,while the other two structures have C1 symmetries .Besides ,the calculated absorption spectra and emission spectra of H (C4 H2 S)n H agree very well with relevant experimental val-ues .%应用密度泛函理论，在B3LYP/6-31G（d）和CAM-B3LYP/6-31G（d）水平上优化了α-联噻吩体系 H（C4 H2S）nH （n ＝2～13）的基态几何构型；与此同时，利用TD-B3LYP方法计算了H（C4 H2S）nH的吸收光谱，得到了其垂直激发能和体系大小 n的解析表达式；并采用 TD-CAM-B3LYP方法研究了其发射光谱。研究表明， H （C4 H2 S ）n H的基态结构呈现三种构型：螺旋上升型、环型和稍有弯曲的带状结构；其中前两种构型是顺式结构，最后一种构型是反式结构；环型结构具有 C2对称性，其他两种结构具有 C1对称性。此外，其吸收光谱和发射光谱计算值与实验值吻合。
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