title: Electrochemical, spectroelectrochemical, and molecular quadratic and cubic nonlinear optical properties of alkynylruthenium dendrimers.
abstract: A combination of cyclic voltammetry (CV), UV-vis-NIR spectroscopy and spectroelectrochemistry, hyper-Rayleigh scattering (HRS) [including depolarization studies], Z-scan and degenerate four-wave mixing (DFWM) [including studies employing an optically transparent thin-layer electrochemical (OTTLE) cell to effect electrochemical switching of nonlinearity], pump-probe, and electroabsorption (EA) measurements have been used to comprehensively investigate the electronic, linear optical, and nonlinear optical (NLO) properties of nanoscopic pi-delocalizable electron-rich alkynylruthenium dendrimers, their precursor dendrons, and their linear analogues. CV, UV-vis-NIR spectroscopy, and UV-vis-NIR spectroelectrochemistry reveal that the reversible metal-centered oxidation processes in these complexes are accompanied by strong linear optical changes, "switching on" low-energy absorption bands, the frequency of which is tunable by ligand replacement. HRS studies at 1064 nm employing nanosecond pulses reveal large nonlinearities for these formally octupolar dendrimers; depolarization measurements are consistent with lack of coplanarity upon pi-framework extension through the metal. EA studies at 350-800 nm in a poly(methyl methacrylate) matrix are consistent with the important transitions having a charge-transfer exciton character that increases markedly on introduction of peripheral polarizing substituent. Time-resolved pump-probe studies employing 55 ps, 527 nm pulses reveal absorption saturation, the longest excited-state lifetime being observed for the dendrimer. Z-scan studies at 800 nm employing femtosecond pulses reveal strong two-photon absorption that increases significantly on progression from linear complex to zero- and then first-generation dendrimer with no loss of optical transparency. Both refractive and absorptive nonlinearity for selected alkynylruthenium dendrimers have been reversibly "switched" by employing the Z-scan technique at 800 and 1180 nm and 100-150 fs pulses, together with a specially modified OTTLE cell, complementary femtosecond time-resolved DFWM and transient absorption studies at 800 nm suggesting that the NLO effects originate in picosecond time scale processes.
authors.affiliation: Department of Chemistry and Laser Physics Centre, Research School of Physical Sciences and Engineering, Australian National University, Canberra ACT 0200, Australia.
authors.forename: Marie P
authors.initials: MP
authors.lastname: Cifuentes
authors.forename: Clem E
authors.initials: CE
authors.lastname: Powell
authors.forename: Joseph P
authors.initials: JP
authors.lastname: Morrall
authors.forename: Andrew M
authors.initials: AM
authors.lastname: McDonagh
authors.forename: Nigel T
authors.initials: NT
authors.lastname: Lucas
authors.forename: Mark G
authors.initials: MG
authors.lastname: Humphrey
authors.forename: Marek
authors.initials: M
authors.lastname: Samoc
authors.forename: Stephan
authors.initials: S
authors.lastname: Houbrechts
authors.forename: Inge
authors.initials: I
authors.lastname: Asselberghs
authors.forename: Koen
authors.initials: K
authors.lastname: Clays
authors.forename: André
authors.initials: A
authors.lastname: Persoons
authors.forename: Takashi
authors.initials: T
authors.lastname: Isoshima