Effect of the coordination to the "Os3(CO)11" cluster core on the quadratic hyperpolarizability of trans-4-(4′-X-styryl)pyridines (X = NMe2, t-Bu, CF3) and trans,trans-4-(4′-NMe2-phenyl-1,3-butadienyl)pyridine

Coordination to the "Os-3(CO)(11)" cluster core of substituted styrylpyridines such as trans-4-(4'-NMe2-styryl)pyridine (L-1), trans-4-(4'-t-Bu-styryl)pyridine (L-2), trans-4-(4'-CF3-styryl)-pyridine (L-3), or trans, trans-4-(4'-NMe2-phenyl-1,3-butadienyl)pyridine (L-4) produces an enhancement of their quadratic hyperpolarizability, beta(EFISH), measured by the solution-phase dc electric-field-induced second harmonic (EFISH) generation method. This effect is due either to a red-shift of the intraligand charge-transfer (ILCT) transition upon coordination (when the substituent in para position is a strong electron donor) or to a metal-to-ligand charge-transfer (MLCT) transition (when the substituent is a strong electron acceptor). In the latter case the quadratic hyperpolarizability has a negative sign, due to the negative value of Deltamu(eg). Therefore the "Os-3(CO)(11)" cluster core displays an ambivalent acceptor or donor role. Some of the complexes investigated in this study show significant values (between 500 x 10(-48) and 900 x 10(-48) esu) of the product mubeta(0).