Comparison of the non-linear optical properties of a dimethylaminostilbenederivative containing a molybdenum mononitrosyl redox centre and of p,p '-dimethylaminonitrostilbene, calculated by ab-initio methods

Dipole moments, linear and non-linear polarizabilities of [Mo(NO){HB(dmpz)( 3)}Cl{OC6H4[CH=CHC6H4N(CH3)(2)-4]-4} (dmpz = 3,5-dimethylpyrazolyl) (DMAMoS ) and p,p'-dimethylaminonitrostilbene (DMANS) calculated at the SCF and sec ond-order Moller-Plesset correlation (MP2) level with an effective core pot ential (ECP) basis set are reported. It is shown for DMANS that the ECPs ar e as accurate as calculations using all-electron basis sets of comparable q uality. The effect of diffuse functions on the dominant components of the h yperpolarizabilities of DMANS is small. The dipole moment and linear polari sabilities of DMANS are in very good agreement with experimental values. Th e calculated hyperpolarisabilities are much smaller than the reported exper imental values, but there are large uncertainties among the latter concerni ng calibration factors, concentration dependence and permanent local field effects, which render direct comparison difficult. Electronic correlation e ffects on the hyperpolarisabilities are large, especially for DMAMoS, for w hich the dominant component of the first hyperpolarisability increases by a factor of 5. Generally, the hyperpolarisabilities of DMANS are found to be larger than those of DMAMoS, in spite of the highly polarisable electronic charge-transfer character of the latter.