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A new series of strongly coupled oscillators based upon (porphinato)Pd, (porphinato)Pt, and bis(terpyridyl)ruthenium(II) building blocks is described. These RuPPd , RuPPt , RuPPdRu , and RuPPtRu chromophores feature bis(terpyridyl)Ru(II) moieties connected to the (porphinato)metal unit via an ethyne linker that bridges the 4'-terpyridyl and porphyrin macrocycle meso -carbon positions. Pump-probe transient optical data demonstrate sub-picosecond excited singlet-to-triplet-state relaxation. The relaxed lowest-energy triplet (T 1 ) excited states of these chromophores feature absorption manifolds that span the 800-1200 nm spectral region, microsecond triplet-state lifetimes, and large absorptive extinction coefficients [ε(T 1 → T n ) > 4 × 10 4 M -1 cm -1 ]. Dynamic hyperpolarizability (β λ ) values were determined from hyper-Rayleigh light scattering (HRS) measurements carried out at several incident irradiation wavelengths over the 800-1500 nm spectral region. Relative to benchmark RuPZn and RuPZnRu chromophores which showed large β HRS values over the 1200-1600 nm range, RuPPd , RuPPt , RuPPdRu , and RuPPtRu displayed large β HRS values over the 850-1200 nm region. Generalized Thomas-Kuhn sum (TKS) rules and experimental hyperpolarizability values were utilized to determine excited state-to-excited state transition dipole terms from experimental electronic absorption data and thus assessed frequency-dependent β λ values, including two- and three-level contributions for both β zzz and β xzx tensor components to the RuPPd , RuPPt , RuPPdRu , and RuPPtRu hyperpolarizability spectra. These analyses qualitatively rationalize how the β zzz and β xzx tensor elements influence the observed irradiation wavelength-dependent hyperpolarizability magnitudes. The TKS analysis suggests that supermolecules related to RuPPd , RuPPt , RuPPdRu , and RuPPtRu will likely feature intricate dependences of experimentally determined β HRS values as a function of irradiation wavelength that derive from substantial singlet-triplet mixing, and complex interactions among multiple different β tensor components that modulate the long wavelength regime of the nonlinear optical response.

Six new dicationic 2D nonlinear optical (NLO) chromophores with pyrazinyl-pyridinium electron acceptors have been synthesized by nucleophilic substitutions of 2,6-dichloropyrazine with pyridyl derivatives. These compounds have been characterized as their PF(6)(-) salts by using various techniques including electronic absorption spectroscopy and cyclic voltammetry. Large red shifts in the intense, π → π* intramolecular charge-transfer (ICT) transitions on replacing -OMe with -NMe(2) substituents arise from the stronger π-electron donor ability of the latter. Each compound shows a number of redox processes which are largely irreversible. Single crystal X-ray structures have been determined for five salts, including two nitrates, all of which adopt centrosymmetric packing arrangements. Molecular first hyperpolarizabilities β have been determined by using femtosecond hyper-Rayleigh scattering at 880 and 800 nm, and depolarization studies show that the NLO responses of the symmetric species are strongly 2D, with dominant "off-diagonal" β(zyy) components. Stark (electroabsorption) spectroscopic measurements on the ICT bands afford estimated static first hyperpolarizabilities β(0). The directly and indirectly derived β values are large, and the Stark-derived β(0) response for one of the new salts is several times greater than that determined for (E)-4'-(dimethylamino)-N-methyl-4-stilbazolium hexafluorophosphate. These Stark spectroscopic studies also permit quantitative comparisons with related 2D, binuclear Ru(II) ammine complex salts.

Amphiphilic donor-acceptor meso-ethynyl porphyrins with polar pyridinium electron-acceptor head groups and hydrophobic dialkyl-aniline electron donors have high molecular hyperpolarizabilities (as measured by hyper-Rayleigh scattering) and high affinities for biological membranes. When bound to water droplets in dodecane, or to the plasma membranes of living cells, they can be used for second harmonic generation (SHG) microscopy; an incident light of wavelength 840 nm generates a strong frequency-doubled signal at 420 nm. Copper(II) and nickel(II) porphyrin complexes give similar SHG signals to those of the free-base porphyrins, while exhibiting no detectable two-photon excited fluorescence.