MOLECULAR LINEAR AND QUADRATIC NONLINEAR-OPTICAL PROPERTIES OF PENTAAMMINERUTHENIUM COMPLEXES OF COUMARIN DYES

The ruthenium(II) complex salts [Ru(NH3)(5)L][PF6](2) [L = coumarin 51 0(C-510) 1 or coumarin 523 (C-523) 2] have been synthesized and fully characterized, Their Ru-III analogues [Ru(NH3)(5)L][PF6](3) (L = C-510 3 or C-523 4) have been prepared by oxidation of 1 or 2, respectively , with AgO2CCF3. Electronic spectroscopy and cyclic voltammetry have s hown that the ruthenium centres exert an electron-withdrawing influenc e on the dyes, which is greater for C-523. The intense, low-energy int ramolecular charge-transfer (i.c.t.) absorptions of the C-523 complexe s displayed marked solvatochromism, whilst those of the C-510 complexe s showed only very slight solvent dependence. Measurements of the firs t hyper-polarizability, beta, by using the hyper-Rayleigh scattering t echnique at 1064 nm yielded large values in the range(120-420) x 10(-3 0) esu, the largest being for [Ru(NH3)(5)-(C-523)][PF6](2) 2. These we re enhanced by resonance via the i.c.t. excitations. Correction for re sonance effects by using the two-level model afforded static hyper-pol arizabilities (beta(0)) in the range 35-49 x 10(-30) esu, with [Ru(NH3 )(5)-(C-523)][PF6](3) 4 having the largest. The beta(0) value for 4 wa s larger than that determined for C-523 via electric-field-induced sec ond harmonic generation, indicating that complexation of a {Ru(NH3)5}( 3+) moiety enhanced the hyper-polarizability of this dye. This has bee n ascribed to the electron-withdrawing effect of the Ru-III centre.