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In molecular rotors, a type of molecular machine, spontaneous rotors without the need for an external stimulus are promising because conventional molecular rotors require a continuous energy supply. In this study, we demonstrate spontaneous transformation from kinetically favored metastable right-handed helical aggregates to thermodynamically stable left-handed helical aggregates after an evaporation procedure. In addition, we propose the conditions for preparation of metastable right-handed helical aggregates, whose chirality can be spontaneously inverted, based on kinetic analysis. This molecular power spring will be useful for designing new types of molecular machines.

We demonstrate the evaporation rate-based selection of supramolecular chirality for the first time. P-type aggregates prepared by fast evaporation, and M-type aggregates prepared by slow evaporation are kinetic and thermodynamic products under dynamic reaction conditions, respectively. These findings provide a novel solution reaction chemistry under the dynamic reaction conditions.

Rare earth atoms exhibit several interesting properties, for example, large magnetic moments and luminescence. Introducing these atoms into a different matrix can lead to a material that shows multiple interesting effects. Holmium atoms were incorporated into an iron oxide nanoparticle and the concentration of the dopant atom was changed in order to determine its influence on the host crystal. Its magnetic and magneto-optical properties were investigated by vibrating sample magnetometry and Faraday rotation measurements. The luminescent characteristics of the material, in solution and incorporated in a polymer thin film, were probed by fluorescence experiments. ispartof: Materials vol:7 issue:2 pages:1155-1164 ispartof: location:Switzerland status: published

We studied the adsorption kinetics of supported ultrathin films of dye-labeled polystyrene (l-PS) by combining dielectric spectroscopy (DS) and the interface-specific nonlinear optical second harmonic generation (SHG) technique. While DS is sensitive to the fraction of mobile dye moieties (chromophores), the SHG signal probes their anisotropic orientation. Time-resolved measurements were performed above the glass transition temperature on two different sample geometries. In one configuration, the l-PS layer is placed in contact with the aluminum surface, while in the other one, the deposition is done on a strongly adsorbed layer of neat PS. From the time dependence of the dielectric strength and SHG signal of the l-PS layer in contact with the metal, we detected two different kinetics regimes. We interpret these regimes in terms of the interplay between adsorption and orientation of the adsorbing labeling moieties. At early times, dye moieties get adsorbed adopting an orientation parallel to the surface. When adsorption proceeds to completeness, the kinetics slows down and the dye moieties progressively orient normal to the surface. Conversely, when the layer of l-PS layer is deposited on the strongly adsorbed layer of neat PS, both the dielectric strength and the SHG signal do not show any variation with time. This means that no adsorption takes place.

Recently, much research has been performed on developing low-bandgap polymers for e.g. harvesting solar energy. In the quest to improve these properties, little attention has been paid to their nonlinear optical properties, despite their interesting linear optical spectra and structural similarities to certain nonlinear optically active compounds. We characterized the optical second harmonic generation of corona poled films of poly(cyclopenta[2,1-b;3,4-b′] dithiophen-4-ylidenedioctylmalonate). The unexpectedly large nonlinear optical susceptibilities and the thermal and temporal stability of the material compare favorably to other novel nonlinear optical materials despite the lack of a donor-acceptor dye. Additionally, the polymer displays a very low absorption in the relevant wavelength region. These results demonstrate the promise of these materials for nonlinear optical devices. publisher: Elsevier articletitle: Optical second harmonic generation in a low-bandgap polymer journaltitle: Materials Chemistry and Physics articlelink: http://dx.doi.org/10.1016/j.matchemphys.2014.06.003 content_type: article copyright: Copyright © 2014 Elsevier B.V. All rights reserved. ispartof: Materials Chemistry and Physics vol:147 issue:3 pages:356-359 status: published

Recent research has focused on developing low-bandgap polymers for harvesting solar energy, fine-tuning desirable properties including power conversion efficiency, carrier mobilities and broad light absorption. However, little attention has been paid to their nonlinear optical properties. We characterized the optical second harmonic generation of corona poled films of poly(cyclopenta[2,1-b;3,4-b']dithiophen-4-ylidenedioctylmalonate). Despite being amorphous and lacking a typical donor-acceptor dye, these films display large nonlinear optical susceptibilities. Coupled with their stability and low absorption in the relevant wavelength region, these polymer films compare favorably to other materials. Our results show the promise of low-bandgap polymers for nonlinear optical applications.

A Certified Reference Material (CRM) for determination of aromatic hydrocarbons in air was developed. The CRM 562 consists of aromatic hydrocarbons sorbed on charcoal in glass tubes. Initial feasibility studies established that a homogeneous and stable batch could be prepared. Three intercomparisons prior to the certification allowed the identification of various sources of error. Then, a batch of about 3000 tubes was charged and certified on the basis of analyses carried out in 15 European laboratories. The preparation of the reference material and the results of the certification exercise is described. An overview on the analytical techniques used and the quality control guidelines are also presented. The certified values are 15.0 ± 0.4 μg benzene, 147.3 ± 3.8 μg toluene, 96.4 ± 2.5 μg m-xylene and 93.0 ± 2.9 μg o-xylene per tube. This reference material is recommended for quality control of measurements in the field of occupational hygiene.

Regioregular poly(3-hexylthiophene)s with chain lengths varying from 5 to 100 monomers are synthesized. Poly(3-hexylthiophene)s show in solution an unexpectedly significant second-order nonlinear optical response. The increase in transition dipole moment upon oligomerisation causes the significant second-order nonlinear optical response. crosscheck: This document is CrossCheck deposited related_data: Supplementary Information copyright_licence: The Royal Society of Chemistry has an exclusive publication licence for this journal copyright_licence: The accepted version of this article will be made freely available after a 12 month embargo period history: Received 22 October 2013; Accepted 16 January 2014; Accepted Manuscript published 16 January 2014; Advance Article published 30 January 2014; Version of Record published 13 February 2014 ispartof: Chemical Communications vol:50 issue:21 pages:2741-2743 ispartof: location:England status: published

We describe a technique to optically characterize superparamagnetism. Faraday rotation measurements are performed on a superparamagnetic nanocomposite using small alternating current magnetic fields. The superparamagnetism of the iron oxide nanoparticles causes signals at the uneven harmonics of the magnetic field frequency. These signals provide information on the magnetic moment of the superparamagnetic nanoparticles. Dia- and paramagnetism do not cause signals at higher harmonics, resulting in a high sensitivity to superparamagnetism, even in samples with large dia- or paramagnetic contributions. This technique provides a rapid, economical method to characterize superparamagnetism in composite samples not easily accessible by other techniques. ispartof: Applied Physics Letters vol:102 issue:16 pages:161903-161903 status: published

Faraday rotation, the rotation of the polarization of light due to a magnetic field in the direction of propagation of the light, is used in applications ranging from quantum memory to the detection of biomagnetic fields. For these applications large Faraday rotation is necessary, but absorption of light is detrimental. In search of these properties, we have characterized the Verdet constant of a so far unexplored class of mesogenic organic molecules. We report their spectra and provide an interpretation. A Verdet constant of almost 2.5 × 105 deg T–1 m–1 is found around 520 nm. This Verdet constant is 3 orders of magnitude larger than the largest known for organic molecules in a region without spectral features. We attribute this enormous Faraday rotation to resonant enhancement by a triplet excitation that does not appear in the linear absorption spectrum and to near-resonant enhancement by low-energy singlet excitations. Furthermore we are able to switch the Faraday rotation by changing the liquid crystal phase of the compound. These results demonstrate a new class of Faraday rotating materials with great potential to replace current materials and improve existing applications. The inherent flexibility in the synthesis of this class of molecules opens a new field of research in Faraday rotation. ispartof: Chemistry of Materials vol:25 issue:7 pages:1139-1143 status: published

Clusters of iron oxide and gold nanoparticles dispersed in a polymer show Langevin behavior in magnetization-induced second harmonic generation measurements. Contrary to Faraday rotation, the Faraday ellipticity spectrum shows a feature near the plasmon wavelength.

Magneto-optically active organic compounds are of great technological interest. In contrast to inorganic materials, used in most current applications, organic materials have the advantages of fast response times, easy processing, low cost and abundant resources of starting materials available. Conjugated organic molecules or polymers have been reported to be eligible candidates for exhibiting magneto-optical responses. As part of an ongoing search in our group for efficient magneto-optical materials, eight organic conjugated dyes were screened for their Faraday rotation responses. Based on the obtained preliminary results, it is expected that planar, efficiently pi-conjugated molecules have a higher chance for exhibiting significant magneto-optical responses. Further research will be undertaken to confirm this hypothesis. ispartof: pages:1- ispartof: Nonlinear optics and applications vi vol:8434 pages:1- ispartof: Conference on Nonlinear Optics and Applications VI Brussels, BELGIUM, APR 16-18, 2012 location:Brussels date:16 Apr - 18 Apr 2012 status: published

We have measured the magnetization-induced second harmonic generation (MSHG) of a nanocomposite consisting of iron oxide nanoparticles in a polymer film. The existing theoretical framework is extended to include DC magnetic fields in order to characterize the MSHG signal and analyze the measurements. Additionally, magnetic hysteresis loops are measured for four principal polarizer-analyzer configurations, revealing the P-IN-P-OUT and S-IN-P-OUT polarizer-analyzer configurations to be sensitive to the transverse magnetic field. These results demonstrate the use of MSHG and the applied formalism as a tool to study magnetic nanoparticles and their magnetic properties. (C) 2012 Optical Society of America ispartof: Applied optics vol:51 issue:2 pages:209-213 ispartof: location:United States status: published

A homogeneous and stable reference material consisting of aromatic hydrocarbons sorbed on Tenax in stainless-steel sample tubes has been prepared and certified. An initial feasibility trial established that a homogeneous and stable batch could be prepared. Part of this batch was used in an intercomparison, which allowed the identification of various sources of error. A second test batch was used in a second intercomparison in an attempt to improve the analytical performance of the participating laboratories. A third batch (of 1000 tubes) was then prepared and certified on the basis of analyses carried out in ten laboratories. The certified values for benzene, toluene and m-xylene are, respectively, 1.053 ± 0.014, 1.125 ± 0.015 and 1.043 ± 0.015 µg per tube. This Community Bureau of Reference (BCR) Certified Reference Material 112 is recommended for quality control and for calibration purposes.