Bertil Eliasson

Synthesis, Structure, Spectroscopic Studies, and Complexation of Novel Crown Ether Butadienyl Dyes

Butadienyl dyes of the benzothiazole series with various fragments of benzocrown ethers 1a-c were synthesized for the first time. The structures and spectral properties of crown-containing butadien ...

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.

Comparison of monolayer films of stearic acid and methyl stearate on an Al2O3 surface

Both stearic acid and methyl stearate chemisorbs onto an oxide surface of aluminum with an asymmetric coordination of the carboxylate group as concluded from infrared (IR) spectroscopy data. Similarities in the IR spectra of the films from the two compounds suggest that the ester is bonded in the same way as the acid, and that the ester therefore undergoes hydrolysis during the surface reaction. X-Ray photoelectron spectroscopy (XPS) and IR data are interpreted in terms of self-assembled monolayer formation and a more dense film from the carboxylic acid in comparison with that from the ester.

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.

Triplet excited states of some thiophene and triazole substituted platinum(II) acetylide chromophores

The photophysical properties of a series of platinum(II) acetylide compounds (trans-Pt(PBu(3))(2)(C[triple bond]C-R)(2)) with the R group consisting of two or three aryl rings (phenyl, phenyl/thiophenyl, phenyl/triazolyl) linked together with ethynyl groups were systematically investigated. Four new structurally similar compounds are reported with: (i) a bithiophene unit in the ligands, (ii) methyl or (iii) methoxy substituents on the aryl ring ligands that promote a more twisted conformation along the long axis of the molecule, and (iv) with two different alkynylaryl ligands giving rise to an asymmetric substitution with respect to the photoactive metal ion center. The spectroscopic studies include optical absorption, spectrally and time-resolved luminescence, as well as transient absorption spectra. The ground-state UV absorption between 300 and 420 nm gave rise to fluorescence with quantum efficiencies in the range of 0.1-1% and efficient intersystem crossing to triplet states. Phosphorescence decay times were in the order of 10-500 micros in oxygen-evacuated samples. The triplet states also lead to strong broadband triplet-triplet absorption between 400 and 800 nm. The complex with asymmetric substitution was found to populate two triplet states of different structure and energy.

Unusually low 13C chemical shift sensitivity to charge in cyclic 4nπ anions. Potential relation to anisotropic ring current effects

For various pairs of neutral π-systems and their corresponding di- or tetra-anions, a relationship between the 13C n.m.r. chemical shift/charge ratio (KC) and the altered 1H ring current anisotropy is observed. Thus for a 4nπ anion system, the 13C shift sensitivity to charge is significantly lower than the KC value obtained for a diatropic anion. This is explained in terms of the average electronic excitation energy, which influences both the 13C chemical shifts and the ring current intensities. An empirical model which describes the 13C shifts on the basis of a charge term and an anisotropy term is postulated. The anisotropy term is shown to be linearly related to the 1H ring current anisotropy.

N.M.R. studies of phenyl-substituted group 4 anions. Ion-pairing and charge delocalization vs. π-polarization effects

The n.m.r. chemical shifts of phenyl-substituted silyl, germyl, stannyl, and plumbyl anions show that the remote phenyl carbon positions are mainly affected by π-polarizing effects and that conjugative effects are unimportant in these anionic systems.

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.

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.

Crown-containing styryl dyes: cation-induced self-assembly of multiphotochromic 15-crown-5 ethers into photoswitchable molecular devices

The s-conformations of trans-1b–e were studied by 1H NMR spectroscopy in CD3CN solution. It was shown that in trans-1b–e intramolecular ion pairs between the SO3– group and the positively charged nitrogen atom of the benzothiazolium residue are formed. In the case of trans-1a no ionic association was observed. The complex formation of the trans- and cis-isomers of crown-containing styryl dyes with Mg2+ in CH3CN was studied spectrophotometrically. The anion-“capped” complexes formed by the cis-isomers were found to be more stable than the complexes formed by the corresponding trans-isomers. The stability constants of the complexes formed by the cis-isomers depend markedly on length and type of the N-substituent. Data from PM3 quantum-chemical calculations were used for the interpretation of some experimental data.