Cholesteric polysiloxanes containing an azo dye were irradiated with linearly or circularly polarized laser light or with the unpolarized light from a HgXe lamp. Photoinduced rotational diffusion was observed leading to new textures with a completely different orientational distribution of the chromophoric and the mesogenic side chains. A broad variety of new structures was detected depending on the polarization state of the light, the helical arrangement of the azo dye and the optional application of an electrical d.c. field. The new structures were characterized by spectroscopy with polarized light. Co-operative reorientation of chromophoric and mesogenic side chains was proven. The formation of a Bragg grating upon short term irradiation with linearly polarized light was observed. Continued irradiation leads in most cases to a strongly birefringent texture with a high dichroic ratio of the azo dye resembling a planar nematic texture. With circularly polarized light or with unpolarized light, a uniaxial homeotropic texture appeared predominantly. The formation of the new textures occurred in the glassy state of the samples leading to new structures with good optical quality and an exceptionally good long-term stability.

Materials with low surface energy are very important in applications that require reduced wetting or adhesion. Monolayers of -CF3 containing compounds possess the smallest surface energy known until now that has to promote surface investigations. Perfluoroalkyl compounds were shown to form a microphase-separated structure due to the immiscibility between the -(CF2)(m)- and the -(CH2)(n)- part. Basing on this concept polyesters with perfluoroalkyl side chains were synthesized. Combined investigations by means of X-ray scattering, molecular modeling, AFM and contact angle measurements were performed to characterize the influence of preparation as well as treatment of spin-coated films and to find a correlation between bulk and surface structure and surface free energy.

By means of PSU/LCP multiblock copolymers with different molecular weights of the blocks in binary solution cast blends it was shown that the interpenetration of the PSU phase of the block copolymer and the PSU matrix leads to a partial miscibility of the blend, if the molecular weight of the PSU segments of the block copolymer exceeds the entanglement molecular weight at least twice. From these results, a certain interdiffusion of the PSU segments of the MBCP's and the PSU homopolymer in their interface was concluded. XR as well as NR experiments were used to examine the behavior of layered systems as a function of the annealing temperature in order Co determine the interfacial thickness between the layers as a measure for the interaction.

This paper reports on frequency jumps of single molecule excitation lines: The first part deals with spontaneous spectral jumps (spectral diffusion) and gives examples of what can be learned from investigations of spectral diffusion about the low temperature physics of amorphous solids. The second part of this article discusses light-induced frequency jumps in the crystalline system terrylene in p-terphenyl where reversible single molecule hole-burning allows the optical manipulation of single absorbers in a remarkably controlled and reproducible fashion. Furthermore we demonstrate how this system permits investigations of one and the same chromophore over a period of a few weeks at least.

The controlled manipulation and switching of single atoms and molecules raise the prospect of ultra-high-density data storage. Switching by motion of a single atom has been reported1, and techniques of single-molecule optical detection and spectroscopy2 in the condensed phase have been refined to a degree that allows the modification of the absorption properties of a single chromophore3. Light-induced jumps in single-molecule excitation frequencies have been reported3,4,5, but in none of these cases could the process be controlled: the jumps varied from molecule to molecule, they were interrupted by spontaneous jumps, and the new excitation frequencies could not be identified unambiguously. Here we report light-induced reversible frequency jumps ofsingle molecules of the aromatic hydrocarbon terrylene embedded in a particular site of a p-terphenyl host crystal6 at temperatures of around 2 K. The changes in absorption frequency for different terrylene molecules were identical (within 0.5%) for all samples studied. Thus we were able to switch single-molecule absorption lines in a controlled way between well-defined frequency positions.

This paper reports spectroscopic investigations of the chromophore terrylene embedded in a matrix of crystalline p-terphenyl. While this system is particularly well suited for single molecule spectroscopy, little is known about the guest site configuration of terrylene. To shed some light on this issue, we employed absorption and fluorescence spectroscopy and compared the experimental data to the results of theoretical calculations. Based on this comparison we suggest a substitution scheme which is in agreement with all the spectroscopic evidence. The dispersed fluorescence spectra of single molecules in the wings of the inhomogeneous distribution deviate significantly from the bulk spectra. This observation is discussed in terms of a host-induced change of the structure and a possible C13 isotopic substitution of the chromophores. Finally we investigated the dynamic host–guest interactions via the temperature-dependent shift and broadening of single molecule excitation lines and found these processes dominated by coupling to characteristic pseudolocal phonon modes of the host, although chromophores in the wings of the inhomogeneous distribution exhibit additional contributions which we attribute to thermal matrix expansion.

Quantum jumps between the excited singlet and tripler states of single terrylene molecules in p-terphenyl are directly observable as interruptions of the fluorescence signal. By analyzing the distributions of interval lengths of bright and dark periods, the absolute values of intersystem crossing parameters for population and depopulation of the triplet state can be determined. It is concluded that quantum optical experiments as described here are a valuable tool to study the photophysical dynamics of single absorbers in solid matrices.

Dilute mixed molecular crystals of pentacene in naphthalene were prepared by cosublimation of the two compounds. Single pentacene molecules could be detected in the thin platelets by fluorescence excitation spectroscopy. By analyzing the exponential decay of the fluorescence intensity autocorrelation function for a single molecule in the microsecond time regime we could determine the population (k(23)) and depopulation (k(31)) rate of the metastable triplet state. The increase of the population rate k(23) by a factor of similar to 4 when compared to pentacene in p-terphenyl is responsible for the weaker fluorescence signals of single pentacene molecules in naphthalene crystals.

BOHR'S notion of quantum jumps between electronic states of an excited atom has now been demonstrated experimentally for single ions confined in radio-frequency traps and interacting with a driving laser field(1-3). In these experiments the fluorescence of a strongly allowed transition was shown to cease abruptly when the ion jumped into a metastable state which was coupled to the common electronic ground state by a weak radiative transition. But attempts to monitor quantum jumps of single molecules have been hampered by the fact that the lifetime of the metastable triplet state was too short in relation to the photon detection rate. By using a system with favourable photophysical parameters-terrylene doped into p-terphenyl crystals(4)-we have now been able to observe directly quantum jumps between electronic states of single terrylene molecules. In contrast to single atoms, here the quantum jumps occur as non-radiative transitions between states of different multiplicity, and are manifested as interruptions of the fluorescence signal. These results demonstrate how single-molecule spectroscopy can reveal truly quantum-mechanical effects in large polyatomic molecules.

We report on the investigation of temperature dependent optical dephasing of single terrylene molecules in a p-terphenyl host crystal using two different techniques. The temperature dependence of the optical linewidth between 2 and 7.2 K can be described by an exponentially activated process with an activation energy Delta E = 18 +/- 2 cm(-1), which is attributed to optical dephasing of the electronic transition by scattering of a pseudolocal mode. By measuring the fluorescence intensity autocorrelation function we demonstrate that the dephasing time of a single terrylene molecule can also be extracted from coherent transients (Rabi oscillations) appearing in the correlation function in the nanosecond time regime. These oscillations experience an increased damping at temperatures above 2 K due to pseudolocal mode-induced pure dephasing.

Terrylene in p-terphenyl represents a promising novel single crystalline system for optical spectroscopy of single impurity molecules at low temperatures. The optical spectra of terrylene in p-terphenyl show four origins in absorption and emission, indicating four crystalline sites. In one of the sites saturated fluorescence count rates of up to 600000 s−1 were measured for single terrylene molecules. From a measurement of the fluorescence autocorrelation function for single terrylene molecules we could determine the populating and depopulating rates of the triplet state. Using the very small populating rate the triplet quantum yield was calculated to be only ~ 10−5.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMeasurement of Optical Dephasing of a Single Terrylene Molecule with Nanosecond Time ResolutionS. Kummer and Th. BascheCite this: J. Phys. Chem. 1995, 99, 47, 17078–17081Publication Date (Print):November 1, 1995Publication History Published online1 May 2002Published inissue 1 November 1995https://doi.org/10.1021/j100047a005RIGHTS & PERMISSIONSArticle Views357Altmetric-Citations43LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (426 KB) Get e-Alerts

We investigated pentacene-doped p-terphenyl crystals with different degrees of disorder as evidenced by the inhomogeneous broadening of the O1-site distribution. Single pentacene molecules were detected in the wings of O1 by fluorescence excitation spectroscopy. The ISC rates for a number of single molecules were determined by measuring the intensity correlation function of the fluorescence photons. We found a dramatic dependence of the distribution of ISC rates on the crystal disorder. The fully saturated fluorescence emission rates as calculated using the SC rates were found to be consistent with the experimentally measured photocount rates.

Single molecule spectroscopy in solids at low temperature is a very rapidly growing field which due to the sensitivity of a single molecule to its truly local environment yields new insights in the structure and dynamics of crystalline and amorphous solids [1,2]. In the first years of SMS a lot of different experimental techniques have been applied to only a few well selected systems. These were the mixed crystalline system pentacene in p-terphenyl, and perylene and terrylene in poly(ethylene). Very recently, it was recognized by several groups that it is important to find new systems to demonstrate the more general applicability of this new and exciting spectroscopy. While there are several - well known - stringent requirements for any specific system to observe single molecule spectra with the fluorescence excitation technique, recent successful experiments proved that there is still a wide variety of systems where SMS can be pursued. Two new systems introduced lately were terrylene in the Shpol’skii matrix hexadecane [3] and Rhodamine 640 in (poly)ethylene [4]. In our group we investigated new crystalline as well as new polymeric systems.

Six compounds have been prepared and their single crystals studied: Ba2RbFe2F9, Ba2CsCo2F9, Ba2ANi2F9 (A = K, Rb, Cs) and Ba2CsZn2F9. They are isostructural with Ba3Re2O9, space group R3mBAR, Z = 3, with cell dimensions of about a = 590, c = 2100 pm. Full X-ray structure refinements (wR < 0.04) yielded the average distances Fe-F = 206.4, Co-F = 205.1, Ni-F = 201.6 and Zn-F = 204.3 pm. However, pronounced splitting (5...9%) is observed into 3 long bridging and 3 short terminal bonds. The resulting honeycomb layer structure [MF3F3/2]2.5- of fac-corner-sharing octahedra is discussed along with relations to hexagonal perovskites 9L-CsCoF3, 2L-CsNiF3 and dinuclear Cs3Fe2F9.

Abstractare obtained as outlined in the scheme.

Three new hydrated fluorides of Mn3+ have been obtained from Ni2+ (or Cu2+) and Mn3+ solutions in 40% hydrofluoric acid: NiMnF5 · 7H2O, CuMnF5 · 7H2O, and Cu3Mn2F12 · 12H2O. The monoclinic symmetries and the lattice constants of the two heptahydrates have been established. The crystal structure of Cu3Mn2F12 · 12H2O has been refined using single-crystal X-ray diffraction data: it is triclinic with space group P1 and parameters a = 7.568(1)Å, b = 7.558(1)Å, c = 8.168(1)Å, α = 91.32°, β = 89.72°, γ = 92.61°, Z = 1; R = 0.046 for 4040 independent reflections. It is isostructural with the homologous V, Cr, and Fe compounds. It can be considered as an inverse perovskite with formulation [MnF6][MnF62][Cu(H2O)4F22]3. Whereas the two heptahydrates are paramagnetic down to 2 K, a spontaneous magnetization occurs below Tc = 3.8 ± 0.2 K for Cu3Mn2F12 · 12H2O. Hypotheses have been proposed to account for the field dependence of the magnetization by taking into account the superexchange mechanisms between two Jahn-Teller ions.

AbstractThe title compounds are prepared by solid state reaction of NaF, CuF2, and CrF3 and FeF3, resp. (closed Au‐crucible, 750‐800 °C, 12 h).

AbstractThe isostructural title compounds, obtained from the binary fluorides by hydrothermal synthesis, crystallize in the triclinic system, space group P1, Z=1.