Cesar Lopes

Click Chemistry for Photonic Applications : Triazole-Functionalized Platinum(II) Acetylides for Optical Power Limiting

Three different triazole-containing platinum(II) acetylide compounds were synthesized by click chemistry and evaluated for their use in optical power limiting (OPL) applications. The triazole unit was incorporated at three different positions within, or at the end of, the conjugation path of the chromophore. The aim is to explore the possibilities of using click chemistry to prepare dendronized chromophores, and to evaluate how the triazole structure affects the photophysical properties and the optical power limiting abilities of these acetylide compounds. It is shown that the concept of click chemistry can be used to attach branched monomer units to ethynyl-phenyl arms by Huisgen 1,3-dipolar cycloaddition, forming triazole units within the chromophore. Photophysical characterization of these triazole-containing materials shows an absorption maximum within the UV-A region and emission through both fluorescence and phosphorescence. Bright phosphorescence was emitted from argon purged samples, and decay measurements thereof showed triplet lifetimes of up to 100 µs. The results from the photophysical characterization suggest that the triazole does break the conjugation path, and in order to gain maximum optical limiting the triazole needs to be placed at the end of the conjugation. All three investigated triazole-containing platinum(II) acetylides show good optical power limiting at 532 nm (10 ns pulse, f/5 set-up, 2 mm cells). The most efficient compound, with the triazole positioned at the end of the conjugation, reaches a defined clamping level of 2.5 µJ for a sample with a concentration of 50 mM in THF and a linear transmission above 80% at 532 nm. These data can be compared to the OPL properties of Zn-based porphyrins or derivatized thiophenes, reaching clamping levels of 6–15 µJ.

Luminescence, Singlet Oxygen Production, and Optical Power Limiting of Some Diacetylide Platinum(II) Diphosphine Complexes

A series of four new trans-diphosphine Pt(II) diacetylide complexes, with a thiophene and two benzenoid rings in each acetylide ligand, have been synthesized and characterized with respect to optical absorption, spectrally and time-resolved luminescence, and optically nonlinear properties such as two-photon absorption cross section and optical power limiting. Density functional theory (DFT) calculations of a few ground state conformations of three Pt(II) diacetylide structures showed similar total energy for each geometry-optimized rotamer but some differences in the vertical excitation energies and in the ligand-to-metal charge-transfer character. The wavelengths of the calculated excitations were found to be red-shifted compared with peaks in the optical absorption spectra, but the general trends and shifts of wavelengths between the different structures are well reproduced. Static emission spectra for degassed samples in THF solution of the larger compounds showed small Stokes shifts and low fluorescence quantum yields, indicating fast intersystem crossing to the triplet manifold. More pronounced differences between the compounds were displayed in the phosphorescence data, in terms of spectral emission wavelengths and decay times. For instance, the phosphorescence decay of the compound with the thiophene ring close to the Pt center was found to be significantly faster than for the other compounds. A possible relationship between triplet lifetime and conformation of the compounds is discussed. It was also demonstrated that the quenching of the excited triplet states in air-saturated samples involves energy transfer to the oxygen triplet state, and subsequent generation of singlet oxygen showing the typical emission at approximately 1275 nm. The amount of produced singlet oxygen followed the phosphorescence yields of the solute molecules. Two-photon absorption cross sections (sigma(2)) were measured and showed values on the order of 10 GM at 780 nm for all compounds. Optical power limiting measurements of the new complexes in THF using 5 ns pulses, showed only slightly better performance at the wavelength of 532 nm compared to that of similar platinum compounds with only two aryl rings in each ligand. At 600 nm the complexes with three aryl rings were significantly better optical limiters than the smaller compounds with two aryl rings in the ligands.

Design and synthesis of multifunctional thiacalixarenes and related metal derivatives for the preparation of sol–gel hybrid materials with non-linear optical properties

Thiacalixarenes bearing phenylazo or ethynylic groups on the lower rims were prepared and fully characterized. The functional groups were chosen for their ability to increase the electron delocalisation over the molecule and to form metal complexes. The formation of complexes between phenylazothiacalixarenes and metal salts (Zn2+, Ag+…), and the synthesis of platinum acetylides from ethynylthiacalixarenes were investigated. Preliminary studies on optical limiting properties for both ligands and complexes is reported. Clamping levels of ∼4 µJ at 532 nm, were observed for both tetra(pentylphenylethynyl)tetrapropoxythiacalix[4]arene (150 mM in THF, 99% transmission) and the platinum complex (30 mM in THF, 83% transmission). A second functionalisation (upper rims) with metal alkoxide groups has also been investigated in order to prepare hybrid materials incorporating the optically active molecule. The same macrocycle core was thus bifunctionalised, and used for its optical properties on one side and as a precursor of an inorganic network for hybrid materials on the other.

Silica Hybrid Sol−Gel Materials with Unusually High Concentration of Pt−Organic Molecular Guests: Studies of Luminescence and Nonlinear Absorption of Light

The development of new photonic materials is a key step toward improvement of existing optical devices and for the preparation of a new generation of systems. Therefore synthesis of photonic hybrid materials with a thorough understanding and control of the microstructure-to-properties relationships is crucial. In this perspective, a new preparation method based on fast gelation reactions using simple dispersion of dyes without strong covalent bonding between dye and matrix has been developed. This new sol-gel method is demonstrated through synthesis of monolithic siloxane-based hybrid materials highly doped by various platinum(II) acetylide derivatives. Concentrations of the chromophores as high as 400 mM were obtained and resulted in unprecedented optical power limiting (OPL) performance at 532 nm of the surface-polished solids. Static and time-resolved photoluminescence of the prepared hybrid materials were consistent with both OPL data and previous studies of similar Pt(II) compounds in solution. The impacts of the microstructure and the chemical composition of the matrix on the spectroscopic properties, are discussed.

Copper(I) alkoxides: preparation and structural characterisation of triphenylmethoxocopper(I) and of an octanuclear form of t-butoxocopper(I)

Two copper(I) alkoxides, the novel compound triphenylmethoxocopper(I) and an octanuclear form of t-butoxocopper(I), have been prepared from mesitylcopper(I) and the relevant alcohol. [Cu-4(OCPh3)(4)]. 2C(6)H(5)CH(3) (1) and [Cu-8((OBu)-Bu-t)(8)] (2) have been characterised by means of crystal structure determination. Compound 1 contains two crystallographically independent triphenylmethoxocopper(I) molecules, each with a planar Cu-4 core. The Cu4O4 unit is butterfly-shaped with the oxygen ligands situated alternately approximately 0.4 Angstrom above and below the plane through the copper atoms, and the triphenylmethyl groups spread out over both sides of the Cu4O4 core. The copper(I) centres are two-coordinated with distances of 1.83(1)-1.86(1) Angstrom and O-Cu-O angles of 169.4(5)degrees. [Cu-8((OBu)-Bu-t)(8)] (2) can be described as being composed of two approximately planar Cu4O4 cores, each with the t-butyl groups bent away in the same direction from the Cu4O4 plane. These units are related to one another by a centre of symmetry and with weak Cu-O interactions of 2.493(5) and 2.536(5) Angstrom, involving four of the eight coppers, thus yielding an octanuclear Cu8O8 core. These four copper(I) centres thus attain T-shaped three-coordination by oxygen, whereas the remaining four are approximately linearly coordinated. The short Cu-O bond lengths in 2 range from 1.844(5) to 1.888(5) Angstrom.

Analysis of the nonlinear transmission properties of some naphthalocyanines

In our search for the definition of new molecular compounds combining low linear absorption with high nonlinear optical absorption in the same wavelength range, we have prepared a series of vanadyl, chloroindium and lead naphthalocyaninato complexes with a relatively low linear optical absorption within the visible range when compared to phthalocyanines, but with similar chemical stability. The transmission properties of these complexes for nanosecond pulses at 532 nm have been evaluated and confronted in both linear and nonlinear regimes. Halogenated naphthalocyanines displayed the best optical-limiting performances. It was also found that an increase in concentration generally results in a reduction of the limiting efficiency of the systems, due to the phenomena of intermolecular aggregation and consequent excited-state quenching.

Countering laser pointer threats to road safety

The market demand for bright laser pointers has led to the development of readily available devices that can pose a threat to road safety. Laser pointers can be involved in accidents caused by laser users who do not realise the dangers involved, but laser pointers can also enable deliberate criminal activity. There are technologies available that can counter the threat in different ways. A number of protective principles are outlined below. Some technologies built upon Liquid Crystal Devices are described in greater detail. Without any knowledge of what laser pointers a potential aggressor has access to, a frequency agile filter seems to be the most promising way to avoid the most severe consequences of dazzle from laser pointers. Protective systems incorporating suitable glasses or visors holding frequency agile filters of this kind however, are not commercially available today.

A theoretical and experimental study of non-linear absorption properties of substituted 2,5-di-(phenylethynyl)thiophenes and structurally related compounds.

Photo-physical properties relevant for optical power limiting in the near-visible and visible regions of the spectrum are reported for a series of substituted diarylalkynyl chalcogenophenes (furans, thiophenes, selenophenes, and tellurophenes). The linear ground and excited state absorption as well as the nonlinear (two-photon) absorption were determined at the time-dependent density functional theory level with use of the hybrid exchange-correlation functionals B3LYP and CAM-B3LYP. A selected number of the theoretically studied molecules were synthesized and characterized experimentally with the use of absorption and luminescence spectroscopy. The photo-physical data are compared to the results from optical power limiting measurements performed in THF solution at a wavelength of 532 nm, with a laser pulse length of 5 ns and pulse energies up to 150 µJ. The best compounds in the present investigation display an energy damping by approximately a factor of 10 at a concentration of 0.010 M.

Products of the reaction between copper(I) phenoxide and triphenylphosphine

Abstract Two phenolatocopper(I) derivatives, viz.[Cu 4 (PPh 3 ) 4 (OPh) 4 ( 1 ) and [Cu 2 (PPh 3 ) 3 (OPh) 2 ] ( 2 ), where Ph = C 6 H 5 , have been prepared by the addition of triphenylphosphine to copper(I) phenoxide, obtained from mesitylcopper(I) and phenol. Characterisation by means of crystal structure determination showed 1 to be a tetramer with a cubane-type Cu 4 O 4 core in which CuO distances range from 2.05(2)–2.26(2) A. Complexes 2 is a μ 2 -phenoxide dimer in which one copper(I) centre is four-coordinated by two phenoxide and two triphenylphosphine ligands, while the other is coordinated by a single triphenylphosphine ligand and thus three-coordinated. Complex 1 crystallises as the solvate [Cu 4 (PPh 3 ) 4 (OPh) 4 ]·(C 6 H 5 CH 3 ) 2 in the monoclinic space group P 2 1 / c with a = 14.822(7), b = 23.160(4), c = 28.193(6) A , β = 98.64(2)°, V = 9569(5) A 3 at −90° C and Z = 4 ; full-matrix least-squares refinement yielded R = 0.082 for 529 parameters and 3931 observed reflections. [Cu 2 (PPh 3 ) 3 (OPh) 2 ] ( 2 ) crystallises in the triclinic space group P 1 with a = 13.948(4), b = 16.846(2), c = 12.480(3) A , α = 94.92(2), β = 110.45(2), γ = 95.96(2)°, V = 2709(2) A at −120° C and Z = 2 ; full-matrix least-squares refinement yielded R = 0.063 for 328 parameters and 2507 observed reflections. The effect of increasing the PPh 3 :CuOPh ratio on the stability of the phenoxide is discussed in terms of the coordination geometry and consequent accessibility of the metal to small molecules.

Photophysical and DFT Characterization of Novel Pt(II)-Coupled 2,5-Diaryloxazoles for Nonlinear Optical Absorption

Several new bis-phosphine platinum(II) complexes with 2,5-diaryl-substituted oxazole-containing alkyne ligands have been synthesized and optically characterized in solution. Measurements of nonlinear absorption showed strong attenuation of laser light at 532 and 600 nm. The light absorption of the Pt complexes was shifted from the near-UV region for the ground state to the red region for the excited triplet state, and was associated with large extinction coefficients. The optical limiting effect can be explained by triplet-triplet excited state absorption in conjunction with fast excited singlet-to-triplet intersystem crossing and slow triplet-to-ground-state decay, in comparison with the pulse length of the laser. DFT calculations show good predictability of the S(0)-S(1) and S(0)-T(1) energy gaps and offer insight into the interaction strength between Pt and the alkyne ligands. The use of this type of ligand, with weak absorption for the Pt(II) complexes in the visual wavelength range as a key feature, enables the possibility to further improve these molecular systems for nonlinear absorption applications.