Theoretical study of the linear and nonlinear optical properties of polyacene-thiolate and polyphenylene-thiolate anions

By using the PM3 parametrization with MOPAC6/FF methodology we have studied the α, β, and γ optical properties of a series of polyacene-thiolates PAT and polyphenylene-thiolate PPT oligomers, with aromatic ring numbers from n=1 to 10. The results show that these compounds exhibit significant optical properties, which increase superlinearly with the number of aromatic rings. We found that for oligomers with n<7, the PPT oligomers possess higher intrinsic nonlinear optical properties (NLO) responses than the PAT ones; and for n>7, the PAT response is higher that of PPT. In this study, we also examined the effect of the position of the sulphur atom in the chain structure, and we found that the position significantly affect the optical properties of both PAT and PPT anions. Additionally, for small number of ring units, the thiolates are more (hyper)polarizable than the phenolate ones.