Basis set and electron correlation effects on static electric properties of 1,3-thiazoles and 1,3-benzothiazoles as potential fragments in push-pull NLO chromophores

Dipole moments mu, static averaged polarizabilities <alpha >, and hyperpolarizabilities beta(vec) of thiazole, benzothiazole, and their dipolar substituted derivatives have been computed by means of B3LYP and MP2 theories with the Pol basis set. Basis set effects have been considered for thiazole, benzothiazole, and doubly substituted thiazole and benzothiazole derivatives at the B3LYP level of theory and in the case of thiazole also at the HF and MP2 levels. Attention has been paid to thiazole geometry effects on the electric properties. The effectiveness of thiazole and benzothiazole as a conjugative pathway between electron donor NH2 and electron acceptor NO2 substituents has been compared with benzene. With one exception, differences in geometry appear to influence only modestly the calculated electric properties. The dipole moment- and polarizability-oriented Sadlej Pol basis set and also its reduced form ZPol basis sets are able to reproduce the aug-cc-pVTZ generated mu, <alpha >, and also beta(vec) at all levels of theory (HF, B3LYP, and MP2) very satisfactorily. All approaches yield almost identical basis set trends. A very good agreement in < h > values between the B3LYP and MP2 approach has been found. While the doubly substituted thiazole derivatives possess smaller beta(vec) calculated at the B3LYP level than at the MP2 level, for doubly substituted benzothiazole derivatives the B3LYP estimates of beta(vec) exceed the MP2 estimates. The trends established by the B3LYP functional parallel the trends obtained with the MP2 method. The 2-nitrobenzothiazole-6-amine and 6-nitrobenzothiazole-2-amine exhibit the largest electric properties from the investigated set of molecules. Thiazole (benzothiazole) as a bridging unit between NH2 and NO2 shows slightly reduced (enhanced) NLO characteristic than pNA. Thiazole behaves as a dipolar bridge rather than just an electron acceptor substituent in singly substituted derivatives. Concerning the charge transfer process, NO2 group interacts better with thiazole than NH2, which can result from the tendency to pyramidization of the NH2 group.