Marek Samoc

Neodymium(III) doped fluoride nanoparticles as non-contact optical temperature sensors

We report that non-contact optical temperature sensing can be achieved with the use of heavily Nd(3+) doped NaYF(4) nanoparticles. The temperature evaluation can be realized either by monitoring the absolute luminescence intensity or by measuring the intensity ratio of the two Stark components of the (4)F(3/2) multiplet in the Nd(3+) ions.

Dynamics of third-order nonlinear optical processes in Langmuir-Blodgett and evaporated films of phthalocyanines

The results of degenerate four‐wave mixing studies performed on evaporated films of metal‐free phthalocyanine and Langmuir–Blodgett films of a silicon phthalocyanine using subpicosecond 602 nm pulses are reported. The third‐order nonlinearity of all the samples is high permitting the observation of the degenerate four‐wave mixing signal from even a monolayer. In both cases, the third‐order nonlinearity has a resonant character and the observed time‐resolved phase conjugate signals provide information on the dynamics of excitons. Simultaneously monitoring first‐ and second‐order diffractions from the transient gratings formed in our samples allowed us to obtain more‐detailed information on the factors influencing the temporal behavior of the nonlinear response. It is concluded that the dynamics of excitons determining the nonlinearity is mainly governed by the presence of bimolecular exciton–exciton interaction. Saturation behavior is observed at high light intensities.

Switching the Cubic Nonlinear Optical Properties of an Electro-, Halo-, and Photochromic Ruthenium Alkynyl Complex Across Six States

The impending breakdown in Moore s law has prompted the search for molecule-based information-processing components such as molecular switches and logic gates. Bistable molecules that afford states possessing distinct linear optical properties (absorbance, fluorescence) and that can be interconverted by chemical, redox, magnetic, or photonic stimuli have attracted considerable interest for Boolean logic operations. In principle, molecular computing could exploit ternary or higher-order digit representations, which would permit smaller device components. “Switchable” molecular properties are also of intense interest for sensor applications. Despite this interest, molecules that can exist in more than two stable and independently addressable states, which could be employed for complex and higher-order logic functions, have been explored significantly less than two-state molecules. One potentially very important procedure to exploit molecular switches is to utilize their cubic nonlinear optical (NLO) properties, and in particular their nonlinear absorption. However, this avenue is also poorly explored and is to date restricted to switching between three states at most, although such switching offers 1) the prospect of broadening the available spectral range (and in particular utilizing telecommunications-relevant wavelengths) and 2) the possibility of enhanced spatial control (compared to linear optical switching) because of the higher-order dependence on the intensity of the incident light. Herein we show that a specific binuclear metal alkynyl complex incorporating a functionalized 5,5’-dithienylperfluorocyclopentene (DTE) bridge can afford six stable and switchable states that possess distinct cubic NLO properties. The complex is comprised of independently addressable modules that respond orthogonally to protic (alkynyl ligandQvinylidene ligand), electrochemical (metal-centered redox: RuQRu), and photochemical (DTE ring-openingQring-closing) stimuli. The six states are interconverted along seven pathways, all of which result in distinct changes to cubic nonlinearity for specific regions of the spectrum. Our results demonstrate that complexes of this type have the potential to be used, among other things, in the construction of multi-input logic gates responding to diverse stimuli across a broad spectral range. The synthesis of the dinuclear ruthenium alkynyl complex oa(II) is depicted in Figure S1 in the Supporting Information. The DTE unit is obtained in the “open” form as its 5,5’diethynyl derivative; the open DTE is thermally stable, and this open form persists through the preparative steps that ultimately afford oa(II). Complete synthetic and characterization details are given in the Supporting Information. Complex oa(II) can be reversibly protonated to the di(vinylidene) complex ov(II), reversibly oxidized to the Ru complex dication oa(III), and photoisomerized with UV light to the closed alkynyl complex ca(II). Complex ca(II) can be reversibly protonated to cv(II) and reversibly oxidized to ca(III) and undergoes photoreversion to oa(II) on irradiation with red light. The vinylidene forms and the oxidized forms undergo reversible photoisomerization under analogous irradiation conditions. Note that oxidation of ruthenium vinylidene complexes with these coligands is an irreversible process, as assessed by cyclic voltammetry, so there is a maximum of six switchable states for this complex. The interconversions of the six stable states of the complex are depicted in Scheme 1, and key spectral data are tabulated in the Supporting Information (Table S1). Cyclic voltammograms and UV/Vis/NIR spectral progressions for the redox processes, the latter acquired with an optically transparent thin-layer spectroelectrochemical (OTTLE) cell and demonstrating stable isosbestic points, are given in the Supporting Information, together with NMR spectra demonstrating spectroscopically complete 1) photoisomerization between the open and closed forms and 2) protonation/deprotonation to afford the vinylidene and alkynyl complex forms, and IR spectra demonstrating spectroscopically complete oxidation from the Ru to the Ru form. Several organometallic alkyne-functionalized DTE complexes have been reported, and the effect of oxidation state on photochromic behavior has been probed, although there was no assessment of the effect of protonation/deprotonation on photochromism. [CpFe(h-C5H4C C DTE C C-hC5H4)FeCp] [11] and [(dppe)CpFe(C C DTE C C)FeCp[*] K. A. Green, Dr. M. P. Cifuentes, T. C. Corkery, Prof. M. G. Humphrey Research School of Chemistry, Australian National University Canberra, ACT 0200 (Australia) Fax: (+ 61)2-6125-0760 E-mail: mark.humphrey@anu.edu.au

Third‐order nonlinearity and two‐photon‐induced molecular dynamics: Femtosecond time‐resolved transient absorption, Kerr gate, and degenerate four‐wave mixing studies in poly (p‐phenylene vinylene)/sol‐gel silica film

Femtosecond response and relaxation of the third‐order optical nonlinearity in a newly developed poly (p‐phenylene vinylene)/sol‐gel silica composite are investigated by time‐resolved forward wave degenerate four‐wave mixing, Kerr gate, and transient absorption techniques using 60 fs pulses at 620 nm. Using a theoretical description of two‐ and four‐wave mixing in optically nonlinear media, it is shown that the results obtained from simultaneous use of these techniques yield valuable information on the real and imaginary components of the third‐order susceptibility. In the composite material investigated here, the imaginary component is derived from the presence of a two‐photon resonance at the wavelength of 620 nm used for the present study. This two‐photon resonance is observed as transient absorption of the probe beam induced by the presence of a strong pump beam. It also provides fifth‐order nonlinear response both in transient absorption and in degenerate four‐wave mixing. The fifth‐order contributio...

Organotransition Metal Complexes for Nonlinear Optics

Publisher Summary This chapter describes the structure and nonlinear optical (NLO) property relationships for organometallic systems. Both quadratic and cubic molecular nonlinearities obtained for specific complexes are extremely large, suggesting that the potential for application of organometallics still remains. The most popular complexes subjected to NLO study are ferrocenyl and alkynyl complexes—reassuring that these are the most stable of organometallics, thereby satisfying an important materials requirement for putative applications. NLO behavior arises from the interaction of electromagnetic fields with matter. The consequent generation of new field components (differing in amplitude, phase, frequency, path, polarization, etc.) is of enormous technological importance for optical devices, with potential applications in data storage, communication, switching, image processing, and computing. These applications have generated a need for materials with exceptional NLO properties and satisfactory materials properties (processing, stability, etc.). Two unit systems are commonly employed in describing NLO properties: the SI (MKS) and the Gaussian (cgs) systems. This chapter describes a number of popular techniques used for the measurement of second- and third-order NLO properties of organometallic molecules.

Enhancement of the photovoltaic performance in PbS nanocrystal:P3HT hybrid composite devices by post-treatment-driven ligand exchange

A methodology for achieving versatile and facile ligand exchange by post-fabrication chemical treatment in PbS nanocrystal:poly(3-hexylthiophene) (P3HT) hybrid composite photovoltaic devices is demonstrated. We report a considerable improvement of the photovoltaic performance after post-fabrication chemical treatment using acetic acid to produce PbS nanocrystals surrounded by short-length ligands. Annealing induced morphological and photovoltaic performance changes in the resulting composite devices were investigated as a function of the annealing time.

Third-order Optical Nonlinearities of Oligomers, Dendrimers and Polymers Derived from Solution Z-scan Studies

Z-scan measurements provide a simple way of determining and comparing the third-order nonlinear properties of chemical compounds, especially if measurements can be done on solutions in common solvents. We discuss advantages of the solution Z-scan technique, e.g. the possibility of in situ studies of electrochemical switching of third-order nonlinearity, and problems encountered on the interpretation of the results, such as those due to thermal nonlinearity and solvent effects.

Twisted π-System Chromophores for All-Optical Switching

Molecular chromophores with twisted π-electron systems have been shown to possess unprecedented values of the quadratic hyperpolarizability, β, with very large real parts and much smaller imaginary parts. We report here an experimental and theoretical study which shows that these twisted chromophores also possess very large values of the real part of the cubic hyperpolarizability, γ, which is responsible for nonlinear refraction. Thus, for the two-ring twisted chromophore TMC-2 at 775 nm, relatively close to one-photon resonance, n(2) extrapolated to neat substance is large and positive (1.87 × 10(-13) cm(2)/W), leading to self-focusing. Furthermore, the third-order response includes a remarkably low two-photon absorption coefficient, which means minimal nonlinear optical losses: the T factor, α(2)λ/n(2), is 0.308. These characteristics are attributed to closely spaced singlet biradical and zwitterionic states and offer promise for applications in all-optical switching.

Organometallic Complexes for Nonlinear Optics Part 25. Quadratic and Cubic Hyperpolarizabilities of some Dipolar and Quadrupolar Gold and Ruthenium Complexes

Abstract The complexes [Au(4-CCC 6 H 4 NO 2 )(L)] [L=PCy 3 ( 1 ), PMe 3 ( 2 )], [(L)Au(μ-4-CCRCC)Au(L)] [R=C 6 H 4 , L=PCy 3 ( 4 ), PPh 3 ( 5 ); R=C 6 H 4 -4-C 6 H 4 , L=PCy 3 ( 7 ), PPh 3 ( 8 )], trans,trans -[RuCl(dppm) 2 (μ-4,4′-CCC 6 H 4 C 6 H 4 CC)RuCl(dppm) 2 ] ( 11 ), trans -[Ru(X)(Y)(dppe) 2 ] [X=Cl, Y=4-CCC 6 H 4 I ( 12 ), 4-CCC 6 H 4 CCSiMe 3 ( 13 ); X=CCPh, 4-CCC 6 H 4 CCH ( 14 )] and { trans -[Ru(CCPh)(dppe) 2 ]} 2 (μ-4,4′-CCC 6 H 4 CCCCC 6 H 4 CC) ( 15 ) have been prepared and their electrochemical (Ru complexes) and nonlinear optical properties assessed. Electronic communication between the metal centers in 10 , 11 and 15 diminishes as the π-delocalizable bridge is lengthened. Quadratic nonlinear optical (NLO) merit increases on replacing triarylphosphine by trialkylphosphine, the relative β values Au(4-CCC 6 H 4 NO 2 )(PPh 3 ) 1 3 being observed. Cubic NLO values are small for the gold complexes and much larger for the ruthenium examples. Complex 15 has the largest σ 2 /MWt (two-photon absorption cross-section/molecular weight) value observed thus far for an organometallic complex.

Bridged Triphenylamine-Based Dendrimers: Tuning Enhanced Two-Photon Absorption Performance with Locked Molecular Planarity

Triphenylamine derivatives bridged by methylene units afford a near planar molecular platform in a series of one dimer and two oligomers exhibiting increased structural rigidity compared to that of their parent triphenylamines. This series of dendrimers show significantly enhanced two-photon absorptions that are up to 3-fold that of triphenylamines with similar molecular size and structure.