Vibrational properties and first hyperpolarizability of cyclopentadiene homologues C4H4XH2 (X = C, Si, Ge, sn): ab initio HF and DFT investigation

Abstract IR and Raman spectra and static electronic and vibrational first hyperpolarisabilities, β , of the cyclopentadiene homologues C 4 H 4 XH 2 (X=C, Si, Ge, Sn) have been calculated by conventional ab initio and DFT-B3LYP methods using Sadlej POL and correlation consistent Dunning basis sets to investigate on the role of the heteroatom on the response property. The pure vibrational contribution to β has been evaluated within the double harmonic oscillator approximation. A clear heavy atom effect was found in the vibrational frequencies and intensities localised on the XH 2 and C–X–C fragments, which decrease and increase, respectively, as the size of the heteroatom increases. Both β e and β v show an increase along the series, the vibrational contribution to β being modest in cyclopentadiene, but substantial in metalloles, especially for silole, where it is about two times greater than the electronic counterpart. The β v / β e ratio is strongly dependent on the basis set, decreasing as the quality of the basis set increases. Both β v and total β e + β v values of the cyclopentadiene homologues are higher than the corresponding ones in the furan series, except for stannole and tellurophene which have close total β e + β v values.