Probing the symmetry of the nonlinear optic chromophore Ru(trans-4,4'- diethylaminostyryl-2,2'-bipyridine)₃²⁺: Insight from polarized hyper- Rayleigh scattering and electroabsorption (Stark) spectroscopy

Polarized hyper-Rayleigh scattering (HRS) has been used to interrogate a putative octupolar 'super' chromophore Ru(trans-4,4'-diethylaminostyryl- 2,2'-bipyridine)₃²⁺. While the hyperpolarizability (β) is impressive, it is apparent from polarized HRS measurements that the symmetry of the excited state, and thus the hyperpolarizability tensor, is best described as dipolar in nature. Electroabsorption (electronic Stark effect) experiments support these findings, implying that changes in dipole moment (Δμ) accompany optical excitation. The measured |Δμ| contributions from both metal-to- ligand charge transfer and intraligand transitions have been used to model the wavelength-dependent hyperpolarizability; reasonable qualitative agreement between experimental results and a simple three-state, two-level dipolar model is obtained.