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 "Os3(CO)11" cluster core of substituted styrylpyridines such as trans- 4-(4'-NMe2-styryl)pyridine (L1), trans-4-(4'-t-Bu-styryl)pyridine (L2), trans-4-(4'-CF3-styryl)- pyridine (L3), or trans,trans-4-(4'-NMe2-phenyl-1,3-butadienyl)pyridine (L4) produces an enhancement of their quadratic hyperpolarizability, BetaEFISH, 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 chargetransfer (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 deltamueg. Therefore the "Os3(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 mubeta0.