Dynamic Structure of Regioregulated Poly(alkylthiophene)s

Stochastic Resonance in Organic Electronic Devices

Stochastic Resonance (SR) is a phenomenon in which noise improves the performance of a system. With the addition of noise, a weak input signal to a nonlinear system, which may exceed its threshold, is transformed into an output signal. In the other words, noise-driven signal transfer is achieved. SR has been observed in nonlinear response systems, such as biological and artificial systems, and this review will focus mainly on examples of previous studies of mathematical models and experimental realization of SR using poly(hexylthiophene)-based organic field-effect transistors (OFETs). This phenomenon may contribute to signal processing with low energy consumption. However, the generation of SR requires a noise source. Therefore, the focus is on OFETs using materials such as organic materials with unstable electrical properties and critical elements due to unidirectional signal transmission, such as neural synapses. It has been reported that SR can be observed in OFETs by application of external noise. However, SR does not occur under conditions where the input signal exceeds the OFET threshold without external noise. Here, we present an example of a study that analyzes the behavior of SR in OFET systems and explain how SR can be made observable. At the same time, the role of internal noise in OFETs will be explained.

Accurate Molecular Orientation Analysis Using Infrared p-Polarized Multiple-Angle Incidence Resolution Spectrometry (pMAIRS) Considering the Refractive Index of the Thin Film Sample

Infrared (IR) p-polarized multiple-angle incidence resolution spectrometry (pMAIRS) is a powerful tool for analyzing the molecular orientation in an organic thin film. In particular, pMAIRS works powerfully for a thin film with a highly rough surface irrespective of degree of the crystallinity. Recently, the optimal experimental condition has comprehensively been revealed, with which the accuracy of the analytical results has largely been improved. Regardless, some unresolved matters still remain. A structurally isotropic sample, for example, yields different peak intensities in the in-plane and out-of-plane spectra. In the present study, this effect is shown to be due to the refractive index of the sample film and a correction factor has been developed using rigorous theoretical methods. As a result, with the use of the correction factor, organic materials having atypical refractive indices such as perfluoroalkyl compounds ( n = 1.35) and fullerene ( n = 1.83) can be analyzed with high accuracy comparable to a compound having a normal refractive index of approximately 1.55. With this improved technique, we are also ready for discriminating an isotropic structure from an oriented sample having the magic angle of 54.7°.

Fringe and Noise Reductions of pMAIRS Spectra Using Principal Component Analysis

Infrared p-polarized multiple-angle incidence resolution spectrometry (pMAIRS) is a promising analytical tool for revealing the molecular orientation quantitatively of each chemical group in a thin film even with surface roughness. The spectra are often disturbed by noise and fringe, however, due to the multiple reflections in the substrate and the film, which makes the quantitative analysis very difficult. Therefore, improvement of the signal to noise (SN) ratio of the spectra is expected. Principal component analysis (PCA), in the present study, is first applied to the noise reduction for pMAIRS spectra of a poly(3-hexylthiophene) spin-coated thin film by employing the spin-speed as the experimental parameter. As a result, high quality pMAIRS spectra are readily obtained, with which highly reliable quantitative discussion is made.

The Impact of Polymer Dynamics on Photoinduced Carrier Formation in Films of Semiconducting Polymers

A better understanding of the carrier formation process in photosemiconducting polymers is crucial to design and construct highly functionalized thin film organic photodevices. Almost all studies published focus on the effect of structure on the photoinduced carrier formation process. Here, we study the dynamics of polymer chain impacts on the carrier formation process for a series of poly(3-alkylthiophene)s (P3ATs) with different alkyl side-chain lengths. The formation of polarons (P) from polaron pairs (PP) was accelerated at a temperature at which the twisting motion of thiophene rings occurs. Among all P3ATs employed, in P3AT with hexyl groups, or poly(3-hexylthiophene) (P3HT), it was easiest to twist the thiophene rings and generate P from PP. The activation energy for P formation was proportional to that of thiophene ring motion. This makes it clear that chain dynamics, in addition to the crystalline structure, is a controlling factor for the carrier formation process in photosemiconducting polymers.

Interactions of hydrogen molecules with complexes of lithium cation and aromatic nitrogen-containing heterocyclic anions

Highly stable salt functional groups consisting of lithium cation and aromatic anions (C n H n N5-n -Li) are studied for hydrogen storage using ab initio calculations, force field development, and grand canonical Monte Carlo simulations. Second-order Møller-Plesset perturbation theory with the resolution of identity approximation calculations are calibrated at the CCSD(T)/complete basis set (CBS) level of theory. The calibrations on different types of binding sites are different, but can be used to correct the van der Waals interactions systematically. The anion and salt functional groups provide multiple binding sites. With increased number of nitrogen atoms in the aromatic anion, the number of binding sites increases but the average binding energy decreases. Among the functional groups considered, CHN4-Li exhibits the largest number of binding sites (14) and a weak average binding energy of 5.7 kJ mol(-1) with CCSD(T)/CBS correction. The calculated adsorption isotherms demonstrate that the introduction of the functional group significantly enhances hydrogen uptake despite relatively weak average binding energy. Therefore, it is concluded that searching for functional groups with the larger number of binding sites is another key factor for enhancing the hydrogen storage capacity, given that other conditions such as free volume and surface area are fixed.