106 research outputs found
Investigation of the long effective conjugation length in defect-free insulated molecular wires
Due to the âinsulationâ of the Ï-conjugated backbones, insulated molecular wires (IMWs) are expected to be applied to various optoelectronic applications and nanotechnology.[1] Recently, Kazunori et al have succeeded in the synthesis of a self-threading polythiophene with a polyrotaxane-like 3D architecture (PSTB, see Figure 1), for which an intrawire hole mobility of 0.9 cm2 Vâ1 sâ1 has been measured.[2] Here, we aim to evaluate the extent of Ï-conjugation along polythiophene backbones sheathed within defect-free âinsulatingâ layers. A comparison between the experimental Raman spectra of the self-threading oligomers (i.e. 2STB-5STB) and the corresponding PSTB polymer indicates that: (i) the ratio of relative intensities of the two most intense Raman bands (I1375/1445) increases with the elongation of the size chain but does not saturate up to the pentamer, and (ii) Ï-conjugation spreads over 17â18 thiophene units in the polymer. Whether the effective conjugation length of the polymer is better described by using the long oligomer extrapolation approach[3] or periodic DFT calculations of the polymer is discussed in detailed by exploiting the very recent potentialities of state-of-the-art quantum chemical simulations of vibrational properties for crystalline solids.[Universidad de MĂĄlaga. Campus de Excelencia Internacional AndalucĂa Tech
Long-term monitoring of the short period SU UMa-type dwarf nova, V844 Herculis
We report on time-resolved CCD photometry of four outbursts of a short-period
SU UMa-type dwarf nova, V844 Herculis. We successfully determined the mean
superhump periods to be 0.05584(64) days, and 0.055883(3) for the 2002 May
superoutburst, and the 2006 April-May superoutburst, respectively. During the
2002 October observations, we confirmed that the outburst is a normal outburst,
which is the first recorded normal outburst in V844 Her. We also examined
superhump period changes during 2002 May and 2006 April-May superoutbursts,
both of which showed increasing superhump period over the course of the plateau
stage. In order to examine the long-term behavior of V844 Her, we analyzed
archival data over the past ten years since the discovery of this binary.
Although photometry is not satisfactory in some superoutbursts, we found that
V844 Her showed no precursors and rebrightenings. Based on the long-term light
curve, we further confirmed V844 Her has shown almost no normal outbursts
despite the fact that the supercycle of the system is estimated to be about 300
days. In order to explain the long-term light curves of V844 Her, evaporation
in the accretion disk may play a role in the avoidance of several normal
outbursts, which does not contradict with the relatively large X-ray luminosity
of V844 Her.Comment: 10 pages, 11 figures, accepted for PAS
The 2006 November outburst of EG Aquarii: the SU UMa nature revealed
We report time-resolved CCD photometry of the cataclysmic variable EG Aquarii
during the 2006 November outburst During the outburst, superhumps were
unambiguously detected with a mean period of 0.078828(6) days, firstly
classifying the object as an SU UMa-type dwarf nova. It also turned out that
the outburst contained a precursor. At the end of the precursor, immature
profiles of humps were observed. By a phase analysis of these humps, we
interpreted the features as superhumps. This is the second example that the
superhumps were shown during a precursor. Near the maximum stage of the
outburst, we discovered an abrupt shift of the superhump period by
0.002 days. After the supermaximum, the superhump period decreased at the rate
of =, which is typical for SU UMa-type dwarf
novae. Although the outburst light curve was characteristic of SU UMa-type
dwarf novae, long-term monitoring of the variable shows no outbursts over the
past decade. We note on the basic properties of long period and inactive SU
UMa-type dwarf novae.Comment: 9 pages, 7 figures, accepted for PAS
Survey of Period Variations of Superhumps in SU UMa-Type Dwarf Novae
We systematically surveyed period variations of superhumps in SU UMa-type
dwarf novae based on newly obtained data and past publications. In many
systems, the evolution of superhump period are found to be composed of three
distinct stages: early evolutionary stage with a longer superhump period,
middle stage with systematically varying periods, final stage with a shorter,
stable superhump period. During the middle stage, many systems with superhump
periods less than 0.08 d show positive period derivatives. Contrary to the
earlier claim, we found no clear evidence for variation of period derivatives
between superoutburst of the same object. We present an interpretation that the
lengthening of the superhump period is a result of outward propagation of the
eccentricity wave and is limited by the radius near the tidal truncation. We
interpret that late stage superhumps are rejuvenized excitation of 3:1
resonance when the superhumps in the outer disk is effectively quenched. Many
of WZ Sge-type dwarf novae showed long-enduring superhumps during the
post-superoutburst stage having periods longer than those during the main
superoutburst. The period derivatives in WZ Sge-type dwarf novae are found to
be strongly correlated with the fractional superhump excess, or consequently,
mass ratio. WZ Sge-type dwarf novae with a long-lasting rebrightening or with
multiple rebrightenings tend to have smaller period derivatives and are
excellent candidate for the systems around or after the period minimum of
evolution of cataclysmic variables (abridged).Comment: 239 pages, 225 figures, PASJ accepte
Thiophene-Fused Tropones as Chemical Warfare Agent-Responsive Building Blocks
We report the synthesis of dithienobenzotropone-based conjugated alternating copolymers by direct arylation polycondensation. Postpolymerization modification by hydride reduction yields cross-conjugated, reactive hydroxyl-containing copolymers that undergo phosphorylation and ionization upon exposure to the chemical warfare agent mimic diethylchlorophosphate (DCP). The resulting conjugated, cationic copolymer is highly colored and facilitates the spectroscopic and colorimetric detection of DCP in both solution and thin-film measurements.United States. Defense Threat Reduction Agency. Chemical and Biological Technologies Department (Grant BA12PHM123
Amplified Spontaneous Emission Properties of Semiconducting Organic Materials
This paper aims to review the recent advances achieved in the field of organic solid-state lasers with respect to the usage of semiconducting organic molecules and oligomers in the form of thin films as active laser media. We mainly focus on the work performed in the last few years by our research group. The amplified spontaneous emission (ASE) properties, by optical pump, of various types of molecules doped into polystyrene films in waveguide configuration, are described. The various systems investigated include N,NâČ-bis(3-methylphenyl)-N,NâČ-diphenylbenzidine (TPD), several perilenediimide derivatives (PDIs), as well as two oligo-phenylenevinylene derivatives. The ASE characteristics, i.e., threshold, emission wavelength, linewidth, and photostability are compared with that of other molecular materials investigated in the literature
Size control and compartmentalization in self-assembled nano-structures of a multisegment amphiphile
Enantioselective component selection in multicomponent supramolecular gels
We investigate a two-component acid-amine gelation system in which chirality plays a vital role. A carboxylic acid based on a second generation l-lysine dendron interacts with chiral amines and subsequently assembles into supramolecular gel fibers. The chirality of the amine controls the assembly of the resulting diastereomeric complexes, even if this chirality is relatively "poor quality". Importantly, the selective incorporation of one enantiomer of an amine over the other into the gel network has been demonstrated, with the R amine that forms complexes which assemble into the most stable gel being primarily selected for incorporation. Thermodynamic control has been proven by forming a gel exclusively with an S amine, allowing the R enantiomer to diffuse through the gel network, and displacing it from the "solidlike" fibers, demonstrating that these gels adapt and evolve in response to chemical stimuli to which they are exposed. Excess amine, which remains unincorporated within the solidlike gel fiber network, can diffuse out and be reacted with an isocyanate, allowing us to quantify the enantioselectivity of component selection but also demonstrating how gels can act as selective reservoirs of potential reagents, releasing them on demand to undergo further reactions; hence, component-selective gel assembly can be coupled with controlled reactivity
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