Comparison of the non-linear optical properties of a dimethylaminostilbene derivative 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[CHCHC6H4N(CH3)2-4]-4} (dmpz = 3,5-dimethylpyrazolyl) (DMAMoS) and p,p′-dimethylaminonitrostilbene (DMANS) calculated at the SCF and second-order Møller–Plesset correlation (MP2) level with an effective core potential (ECP) basis set are reported. It is shown for DMANS that the ECPs are as accurate as calculations using all-electron basis sets of comparable quality. The effect of diffuse functions on the dominant components of the hyperpolarizabilities of DMANS is small. The dipole moment and linear polarisabilities of DMANS are in very good agreement with experimental values. The calculated hyperpolarisabilities are much smaller than the reported experimental values, but there are large uncertainties among the latter concerning calibration factors, concentration dependence and permanent local field effects, which render direct comparison difficult. Electronic correlation effects on the hyperpolarisabilities are large, especially for DMAMoS, for which 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.