The syntheses and electrooptic properties of a new family of nonlinear optical chromophores are reported. These species feature an ethyne-elaborated, highly polarizable porphyrinic component and metal polypyridyl complexes that serve as integral donor and acceptor elements. Examples of this structural motif include ruthenium(II) [5-(4'-ethynyl-(2,2';6',2' '-terpyridinyl))-10,20-bis(2',6'-bis(3,3-dimethyl-1-butyloxy)phenyl)porphinato]zinc(II)-(2,2';6',2' '-terpyridine)(2+) bis-hexafluorophosphate (Ru-PZn); osmium(II) [5-(4'-ethynyl-(2,2';6',2''-terpyridinyl))-10,20-bis(2',6'-bis(3,3-dimethyl-1-butyloxy)phenyl)porphinato]zinc(II)-(2,2';6',2''-terpyridine)(2+) bis-hexafluorophosphate (Os-PZn); ruthenium(II) [5-(4'-ethynyl-(2,2';6',2''-terpyridinyl))-15-(4'-nitrophenyl)ethynyl-10,20-bis(2',6'-bis(3,3-dimethyl-1-butyloxy)phen-yl)porphinato]zinc(II)-(2,2';6',2' '-terpyridine)(2+) bis-hexafluorophosphate (Ru-PZn-A); osmium(II) [5-(4'-ethynyl-(2,2';6',2' '-terpyridinyl))-15-(4'-nitrophenyl)ethynyl-10,20-bis(2',6'-bis(3,3-dimethyl-1-butyloxy)phenyl)porphinato]zinc(II)-(2,2';6',2' '-terpyridine)(2+) bis-hexafluorophosphate (Os-PZn-A); and ruthenium(II) [5-(4'-ethynyl-(2,2';6',2' '-terpyridinyl))osmium(II)-15-(4'-ethynyl-(2,2';6',2''-terpyridinyl))-10,20-bis (2',6'-bis(3,3-dimethyl-1-butyloxy)phenyl)porphinato]zinc(II)-bis(2,2';6',2''-terpyridine)(4+) tetrakis-hexafluorophosphate (Ru-PZn-Os). The frequency dependence of the dynamic hyperpolarizability of these compounds was determined from hyperRayleigh light scattering (HRS) measurements carried out at fundamental incident irradiation wavelengths (lambda(inc)) of 800, 1064, and 1300 nm. These data show that (i) coupled oscillator photophysics and metal-mediated cross-coupling can be exploited to elaborate high beta(0) supermolecules that exhibit significant excited-state electronic communication between their respective pigment building blocks; (ii) high-stability metal polypyridyl compounds constitute an attractive alternative to electron releasing dialkyl- and diarylamino groups, the most commonly used donor moieties in a wide range of established nonlinear optical dyes; (iii) this design strategy enables ready elaboration of chromophores having extraordinarily large dynamic hyperpolarizabilities (beta(lambda) values) at telecommunication relevant wavelengths; and (iv) porphyrin B- and Q-state-derived static hyperpolarizabilities (beta(0) values) can be designed to have the same or opposite sign in these species, thus providing a new means to regulate the magnitude of lambda(inc)-specific dynamic hyperpolarizabilities.

The new salts trans‐4′‐(dimethylamino)‐N‐R‐4‐stilbazolium hexafluorophosphate (R = methyl, Me 1, phenyl, Ph 2, 2,4‐dinitrophenyl, DNPh 3, 2‐pyrimidyl, Pym 4, Scheme 1) have been prepared. Their electronic absorption spectra show intense, visible intramolecular charge‐transfer bands, the energy (Emax) of which decreases in the order R = Me > Ph > DNPh > Pym. This trend arises from the steadily increasing electron deficiency of the pyridinium ring, a phenomenon also observed in cyclic voltammetric and 1H nuclear magnetic resonance (NMR) data. Fluorescence‐free first hyperpolarizability β values of [1–4]PF6 were measured by using femtosecond hyper‐Rayleigh scattering (HRS) with acetonitrile solutions and a 1300 nm laser, and static first hyperpolarizabilities β0 were obtained by application of the two‐state model. The HRS results indicate that the N‐aryl chromophores in [2–4]PF6 have considerably larger β0 values than their N‐methyl counterpart in [1]PF6, with a ca. 10‐fold increase in β0 observed in moving from [1]PF6 to [4]PF6 (25 → 230 × 10–30 esu). Stark (electroabsorption) spectroscopic studies in butyronitrile glasses at 77 K allowed the derivation of dipole moment changes Δμ12 (10.9–14.8 D), which have been used to calculate β0 according to the two‐state equation β0 = 3Δμ12(μ12)2/2(Emax)2 (μ12 = transition dipole moment). With the exception of [1]PF6, the Stark‐derived β0 values are in reasonable agreement with those from HRS. However, the increase in β0 in moving from [1]PF6 to [4]PF6 is only 2‐fold for the Stark data (90 → 185 × 10–30 esu). The observed trend of increasing β0 in the order [1]PF6 < [3]PF6 < [2]PF6 < [4]PF6 arises from a combination of decreasing Emax and increasing Δμ12, with only a slight increase in μ12 between [1]PF6 and [4]PF6. It is likely that the β0 values for [3]PF6 are lower than expected due to the steric effect of the ortho‐NO2 group, which causes twisting of the DNPh ring out of the plane of the stilbazolium unit. A single crystal X‐ray structure shows that [2]PF6 crystallizes in the space group Cc, with head‐to‐tail alignment and almost parallel stacking of the pseudo‐planar stilbazolium portions of the cations to form polar sheets within a polar bulk structure. [2]PF6 is essentially isostructural with the related Schiff base salt trans‐4‐[(4‐dimethylaminophenyl)iminomethyl]‐N‐phenylpyridinium hexafluorophosphate ([8]PF6). Second harmonic generation (SHG) studies on [2]PF6 and [8]PF6 using a 1907 nm laser and sieved powdered samples (53–63 μm) afforded efficiencies of 470 and 240 times that of urea, respectively. Under the same conditions, the well‐studied compound [1]p‐MeC6H4SO3 gave an SHG efficiency of 550 times that of urea.

Low-energy metal-to-ligand charge-transfer (MLCT) excitations are associated with the very large molecular nonlinear optical (NLO) coefficients, β, of the complexes [Ru (NH ) (N-R-4,4'-bipyridinium)] (R=methyl, phenyl, or 4-acetylphenyl). Chemical oxidation to the Ru forms causes bleaching of the MLCT absorptions and marked attenuation of the NLO responses. Both effects are completely reversed upon re-reduction, and the extent of the β switching is about 10- to 20-fold.