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A combination of cyclic voltammetry, UV-vis-NIR spectroelectrochemistry, time-dependent density functional theory (TD-DFT), and Z-scan measurements employing a modified optically transparent thin-layer electrochemical (OTTLE) cell has been used to identify and assign intense transitions of metal alkynyl complexes at technologically important wavelengths in the oxidized state and to utilize these transitions to demonstrate a facile electrochromic switching of optical nonlinearity. Cyclic voltammetric data for the ruthenium(II) complexes trans-[RuXY(dppe)(2)] [dppe = 1,2-bis(diphenylphosphino)ethane, X = Cl, Y = Cl (1), Ctbd1;CPh (2), 4-Ctbd1;CC(6)H(4)Ctbd1;CPh (3); X = Ctbd1;CPh, Y = Ctbd1;CPh (4), 4-Ctbd1;CC(6)H(4)Ctbd1;CPh (5)] show a quasi-reversible oxidation at 0.50-0.60 V (with respect to ferrocene/ferrocenium 0.56 V), which is assigned to the Ru(II/III) couple. The ruthenium(III) complex cations trans-[RuXY(dppe)(2)](+) were obtained by the in situ oxidation of complexes 1-5 using an OTTLE cell. The UV-vis-NIR optical spectra of 1(+)-5(+) contain a low-energy band in the near-IR region ( approximately 8000-16 000 cm(-)(1)), in contrast to 1-5, which are optically transparent at wavelengths < 22 000 cm(-)(1). TD-DFT calculations have been applied to model systems trans-[RuXY(PH(3))(4)] [X = Cl, Y = Cl, Ctbd1;CPh, or 4-Ctbd1;CC(6)H(4)Ctbd1;CPh; X = Ctbd1;CPh, Y = Ctbd1;CPh or 4-Ctbd1;CC(6)H(4)Ctbd1;CPh] to rationalize the optical spectra of 1-5 and 1(+)-5(+). The important low-energy bands in the electronic spectra of 1(+)-5(+) are assigned to the promotion of an electron from either a chloride p orbital or an ethynyl p orbital to the partially occupied HOMO. These absorption bands have been utilized to demonstrate a facile switching of cubic nonlinear optical (NLO) properties at 12 500 cm(-)(1) (corresponding to the wavelength of maximum transmission in biological materials such as tissue) using the OTTLE cell, the first electrochromic switching of molecular nonlinear refraction and absorption, and the first switching of optical nonlinearity using an electrochemical cell.

Membrane plasticization is the process whereby penetrant dissolution causes membrane swelling or dilation, which in turn, can increase membrane diffusivity and solubility and lead to long time frame polymer relaxation processes. In this work, the effect of temperature upon the plasticization of a rigid polyimide, poly(4,4'-hexafluoroisopropylidene diphthalic anhydride-2,3,5,6-tetramethyl-1,4-phenylenediamine) (6FDA-TMPDA), by carbon dioxide is investigated. It is found that across the full range of temperatures studied, plasticization has little effect on carbon dioxide solubility as all results can be characterized by a standard dual mode sorption model. However, the effect upon diffusivity is significant and this can be described by both an exponential relationship with penetrant concentration and an Arrhenius relationship with temperature. The polymer relaxation processes induced by plasticization are also temperature dependent. However, the total proportion of penetrant sorption associated with such relaxation processes is relatively unaffected by temperature. This paper shows that plasticization effects are dominated by Henry's law dissolution. Conversely, while Henry's Law species contribute most to diffusion at high temperatures, at lower temperatures the movement of Langmuir component species also contributes to the total diffusion coefficient.

The molecular inorganic compounds 1,3,5-{trans-[RuCl(dppe)2]C⋮C-4-C6H4C⋮C}3C6H3 (1), trans-[Ru(C⋮C-4-C6H4C⋮CPh)Cl(dppe)2] (2), and trans-[Ru(C⋮CPh)Cl(dppm)2] (3) exhibit reversible oxidation in solution, assigned to the metal-centered RuII/III processes. Complexes 1−3 are essentially transparent at frequencies below 20 × 103 cm-1, whereas the green complexes 1 + −3 + have a strong absorption band centered near 11−12 × 103 cm-1. These absorption bands have been utilized to demonstrate facile NLO switching utilizing an optically transparent thin-layer electrochemical cell, a procedure which has applicability to evaluating the switching capability of a range of materials. This procedure has been applied to switch cubic nonlinearities, the first electrochromic switching of molecular nonlinear absorption. Oxidation of the molecules results in changes, including changes of sign, of both the imaginary (absorptive) part of the third-order nonlinearity and the real (refractive) part. Cycling between the two forms of the molecules is facile. The sign of the nonlinearity is reversed on oxidation of 1 and 2, whereas 3, a complex with negligible third-order nonlinearity in the resting state, has third-order nonlinearity switched on upon oxidation to 3 + .

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.

The “first-generation” alkynylruthenium dendrimers 1,3,5-C6H3(4-C⋮CC6H4C⋮C-trans-[Ru(dppe)2]C⋮C-3,5-C6H3{4-C⋮CC6H4C⋮C-trans-[Ru(4-C⋮CC6H4R)(dppe)2]}2)3 [R = H (19), NO2 (20)], containing nine dialkynylruthenium centers, have been prepared by convergent synthesis. Reaction of 3 equiv of 1-iodo-4-trimethylsilylethynylbenzene with triethynylbenzene, under Sonogashira coupling conditions, followed by deprotection with tetra-n-butylammonium fluoride affords 1,3,5-C6H3(4-C⋮CC6H4C⋮CH)3 (2), which is reacted with cis-[RuCl2(L)2] (L = dppe, dppm) to afford the octopolar, triruthenium dendritic cores 1,3,5-C6H3{4-C⋮CC6H4C⋮C-trans-[RuCl(L)2]}3 [L = dppe (5), L = dppm (6)] via the vinylidene intermediates [1,3,5-C6H3{4-C⋮CC6H4CHC-trans-[RuCl(L)2]}3](PF6)3 [L = dppe (3), L = dppm (4)]. Reaction of 5 with terminal alkynes 4-HC⋮CC6H4R (R = H, NO2, NEt2) affords a series of related dialkynylruthenium zero-generation dendrimers 1,3,5-C6H3{4-C⋮CC6H4C⋮C-trans-[Ru(4-C⋮CC6H4R)(dppe)2]}3 [R = H (7), NO2 (8), NEt2 (9)]. Reaction of 3 equiv of trans-[Ru(4-C⋮CC6H4C⋮CH)(C⋮CPh)(dppe)2] with 1,3,5-triiodobenzene under Sonogashira coupling conditions also affords 7, together with the homo-coupled trans,trans-[(dppe)2(PhC⋮C)Ru(4,4‘-C⋮CC6H4C⋮CC⋮CC6H4C⋮C)Ru(C⋮CPh)(dppe)2]. The first-generation dendrimers 19 and 20 are prepared by coupling core 5 with the dendrons 1-(HC⋮C)C6H3-3,5-{4-C⋮CC6H4C⋮C-trans-[Ru(4-C⋮CC6H4R)(dppe)2]}2 [R = H (17), NO2 (18)]. Thus, reaction of 1-(Me3SiC⋮C)C6H3-3,5-(4-C⋮CC6H4C⋮CH)2 (12), obtained from 1-iodo-3,5-dibromobenzene through a series of Sonogashira coupling and transhalogenation reactions, with cis-[RuCl2(dppe)2] affords 1-(Me3SiC⋮C)C6H3-3,5-{4-C⋮CC6H4C⋮C-trans-[RuCl(dppe)2]}2 (13), which can be reacted with appropriately functionalized terminal alkynes to afford the series 1-(Me3SiC⋮C)C6H3-3,5-{4-C⋮CC6H4C⋮C-trans-[Ru(4-C⋮CC6H4R)(dppe)2]}2 [R = H (14), NO2 (15), NEt2 (16)]. Desilylation of 16 proceeds with decomposition; in contrast, treatment of 14 and 15 with tetra-n-butylammonium fluoride gives 17 and 18, which are coupled with 5 under basic conditions to afford the dendritic complexes 19 and 20 via in situ deprotonation of the vinylidene complex intermediates. A transmission electron micrograph of 19 supported on alumina reveals molecules that are approximately 6 nm in diameter, in agreement with molecular modeling studies.

A study has been conducted to clarify the relationship between polymer structure, annealing temperature, and the extent of plasticization by high‐pressure CO2 for two typical polyimide membranes; BTDA‐DAPI (poly(3,3′‐4,4′‐benzophenone tetracarboxylic–dianhydride diaminophenylindane) and 6FDA‐TMPDA (poly(2,2′‐bis(3,4′‐dicasrboxyphenyl) hexafluoropropane dianhydride–2,3,5,6‐tetramethyl‐1,4‐phenylenediamine). Both membrane materials are exposed to varying levels of thermal annealing at 200 and 250 °C. The effect of this heat treatment on free volume is examined using positron annihilation lifetime spectroscopy (PALS), whereas fluorescence spectroscopy is used to monitor changes in electronic structure. Results show that thermal annealing causes a reduction in both the size and number of free volume elements. A strong relationship is found between the fluorescence peak intensity for 6FDA‐TMPDA and both the membrane gas permeability and plasticization pressure. This correlation is most likely the result of the formation of charge transfer complexes, particularly at 250 °C. However, the formation of covalent crosslinks at these temperatures cannot be discounted. No fluorescence is observed for BTDI‐DAPI. Although thermal annealing has a significant effect on the extent of plasticization in both polymers, it is found that the rate of plasticization is unaffected by the annealing temperature. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1879–1890, 2008