Organometallic complexes for nonlinear optics. 22. Quadratic and cubic hyperpolarizabilities of trans-bis(bidentate phosphine)ruthenium sigma-arylvinylidene and sigma-arylalkynyl complexes

The syntheses of trans-[Ru(C=CHR)Cl(pp)(2)]PF6 (pp = dppm, R = 4-C6H4C=CPh, 4-C6H4CHO, 4,4'-C6H4C drop CC6H4NO2, (E)-4,4'-C6H4CH=CHC6H4NO2, 4,4',4"-C drop CC6H4C drop CC6H4C drop CC6H4NO2; PP = dppe, R = 4-C6H4CHO, (E)-4,4'-C 6H4CH=CHC6H4NO2) and trans-[Ru(C=-CR)Cl(PP)(2)] (pp = dppm, R = 4-C6H4C dro p CPh, 4-C6H4CHO, 4,4-C6H4C dropC(6)H(4)NO(2), (E)4,4'-C6H4CH drop CHC6H4NO 2, 4,4,4"-C drop CC6H4C drop CC6H4C drop CC6H4NO2; pp = dppe, R = 4-C6H4CHO , (E)-4,4-C6H4CH drop CHC6H4NO2) are reported, together with X-ray structur al studies of trans-[Ru(C drop CR)Cl(pp)(2)] (pp = dppm, R = 4-C6H4C drop C Ph; pp = dppe, R = 4-C6H4CHO, (E)-4,4'-C6H4CH drop CHC6H4NO2)- Cyclic volta mmetric, linear optical, and quadratic and cubic nonlinear optical response data for these new complexes, together with the corresponding data for the previously reported trans-[Ru(C=CHR)Cl(pp)(2)]PF6 (pp = dppm, R = Ph, 4-C6 H4NO2; pp = dppe, R = Ph, 4-C6H4NO2) and trans- [Ru(C drop CR)Cl(PP)(2)] (p p = dppm, R = Ph, 4-C6H4NO2, (E)-4,4'-C6H4CH drop CHC6H4NO2; pp = dppe, R = Ph, 4-C6H4NO2), are reported. Oxidation potentials for the Ru-II/III coupl e increase on proceeding from the neutral alkynyl complex to the analogous cationic vinylidene complex and on introduction of an acceptor group (CHO o r NO2); the complexes with 4-C drop CC6H4NO2 ligands are the most difficult to oxidize. In some instances, the Ru-III/IV and Ru-I/II processes have be en identified together with, where relevant, nitro-centered reduction proce sses. The oxidized and reduced vinylidene complexes are shown to transform electrochemically into the corresponding alkynyl complexes. Optical absorpt ion maxima undergo a red shift upon increase of acceptor strength, replacem ent of the coligand dppm with dppe, and replacement of the alkynyl ligand y ne linkage with an ene linkage. Proceeding from the vinylidene complex to a n analogous alkynyl complex results in a small red shift in absorption maxi mum and a significant increase in extinction coefficient. Quadratic molecul ar nonlinearities by hyper-Rayleigh scattering measurements at 1064 nm incr ease upon introduction of ligated metal (proceeding from precursor alkyne t o alkynyl or vinylidene complex), an increase in acceptor strength (introdu ction of CHO or NO2), alkynyl chain lengthening (in the series [4-C drop CC 6H4](n)-4-NO2, proceeding from n = 1 and 2 to 3), and replacing the yne lin kage with an ene linkage. Significant differences in fi value for two vinyl idene/alkynyl complex pairs suggest that they could function as precursors to protically switchable quadratic NLO materials at 1064 nm. Cubic molecular nonlinearities by Z-scan measurements at 800 nm are in many cases characterized by negative real and significant imaginary components, indicative of two-photon effects; nevertheless, a substantial increase in /gamma/ on proceeding to the largest molecule, trans-Ru(4,4,4"-C drop CC6H4 C drop CC6H4C drop CC6H4NO2)Cl(dppm)(2), is observed. An order of magnitude difference in Yinag values (and therefore two-photon absorption (TPA) cros s sections sigma (2)) for vinylidene/alkynyl complex pairs suggest that the y have potential as protically switchable TPA materials at 800 nm.