Thermochromism In Poly Research Articles

Two-step thermochromism in poly(3-docosoxy-4-methylthiophene): Mechanistic similarity to poly(3-docosylthiophene)

Poly(3-docosoxy-4-methylthiophene) (PDMT) was synthesized and investigated. PDMT can form a mesophase by rapid quenching from the isotropic melt. Variable- temperature reflection and fluorescence spectroscopy of thin films and differential scanning calorimetry were used to study the thermal behavior of PDMT. PDMT shows a two- step thermochromic transition from the mesophase, and endotherms in the thermograms could be assigned to melting of each phase. A comparison to with related poly(3-alkylthiophene)s suggests that the mechanism of the thermochromic transition is very similar.

Transport Phenomena of Poly(3-octadecylthiophene) at the Solid-Liquid Phase Transition

We have tried to confirm the sign inversion of electronic photocarrier in a fusible conducting polymer, regiorandom poly(3-octadecylthiophene), PAT18 associated with the solid-liquid phase transition by means of the time-of-flight (TOF) method. It was found that the hole mobility decreases with increasing temperature. At the temperature near the solid-liquid phase transition, the hole mobility decreases drastically, and eventually the melting temperature, it was impossible to evaluate the hole mobility from noisy transient photocurrent. On the other hand, transient photocurrent based on electron transport are observed above the melting point. The negative carrier mobility was evaluated in the range from 10 −6 to 10 −5 cm 2/Vs, which is comparably the hole mobility at solid state. This fact suggests that the same mechanism, for example interchain hopping limits carrier transport, and the negative carrier is electron. This unique phenomenon is interpreted as modulation of electronic energy state caused by conformational change of the main chain. That is, the drastic conformational change of polymer backbone induced by the thermal activation of side chain vibration, which is responsible for the thermochromism in poly(3-alkylthiophene)s, may play a key role for this unique phenomenon.

Observation of Two-Step Thermochromism in Poly(3-docosylthiophene): DSC and Reflection Spectroscopy

Poly(3-docosylthiophene) was found to have a two-step thermochromic process for samples that are rapidly cooled from the melt. The melt-quenched samples are a red-orange color that changes first to purple and then to yellow upon heating. In contrast, slowly cooled materials are purple and have a single thermochromic transition to yellow, typical of most poly(3-alkylthiophene)s. This phase behavior is found in both regioregular and regioirregular samples. The thermal behavior of the polymers was studied using differential scanning calorimetry and visible reflection spectroscopy. The DSC thermograms of slowly cooled samples show two endotherms upon heating and three exotherms upon cooling. In contrast, rapidly cooled samples exhibit three endotherms upon heating and three exotherms upon cooling. Reflection spectra show color changes that correlate with the DSC features. A model is proposed to explain the data that involves trapping of a high-temperature mesophase under the rapid cooling conditions.

The thermochromism of poly(3-alkylthiophene)s: the role of the side chains

A combined atomistic simulation involving static lattice and molecular dynamics simulation methods investigates the structure of poly(3-alkylthiophene)s in order to study their thermochromism. Taking the shortest alkyl chain (butyl) that makes the polymer thermochromic, conformational changes are monitored at different temperatures. The simulations demonstrate that there is a tendency for the side chain to twist between 40 and 70° about the C–C bond linking it to the thiophene ring, although the carbon atoms in the side chain largely retain a trans conformation to above room temperature. These results, and the prediction of a non-zero setting angle, are qualitatively in accord with lattice powder diffraction structures. There is a step-like increase in the mean angle between the thiophene rings as a function of temperature at T=340 K, suggesting the occurence of an abrupt reduction in the planarity of the conjugated chain at this temperature that should lead to an increased band width and thermochromism. This is shown to be concerted with similar changes in side chain torsions at the same temperature, on the basis of which a tentative mechanism for the thermochromism is proposed.

Lattice simulations of thermochromic distortions in poly(alkylthiophene)s

Abstract The thermochromism of poly(3-alkylthiophene)s is explained as a buckling of the main chain by torsions around the inter-ring bonds resulting in a dilation of the π band energy gap. Atomistic simulation calculations show that the necessity to preserve translational periodicity imposes restrictions on the permitted torsions. In our model the effect of heating causes a relative shift of adjacent polymer chains, changing the ring stacking from ‘staggered’ to ‘eclipsed’, in which the chains undergo a spontaneous torsion of 20 °.

Atomistic Investigation of Thermochromism in a Poly(3-alkylthiophene)

In an attempt to explain the mechanism of thermochromism in poly(3-alkylthiophene)s we conducted lattice energy and Monte Carlo calculations to investigate the conformational structures and conformational energy profiles of the butyl side chains. The results reveal barriers of 0.3−0.6 eV (agreeing with the range found experimentally) and predict stable lattice structures in which the butyl side chains are in low-lying well-defined gauche and cis conformations as well as the lowest energy trans. If a thiophene ring is displaced from its regular position in which it is coplanar with its neighbors and the lattice is then allowed to relax to its minimum energy structure, the ring returns to coplanarity only if its alkyl side chain is in an all-trans conformation. If on the other hand the alkyl bears a gauche or a cis linkage, the ring takes up one of a number of out-of-plane distortions coupled with torsions of several degrees around the bonds linking it with its neighbors. A series of ab initio quantum chemi...

Thermochromism of poly (substituted thiophene) with urethane bond and its application to reversible thermal recording

We synthesized a novel poly (substituted thiophene) which has a long alkyl group with a urethane bond at the 3-position of the thiophene ring. The UV-visible absorption and X-ray diffraction methods reveal thermochromic properties of the polymers, which show the possibility of applying them to reversible thermal recording. The color change of the polymer from brownish-red to yellow was fixed by heating and quenching to room temperature (heat-quenching method). The fixed yellow color returned to the initial color of brownish-red after annealing at 100 °C (annealing method).

Order and thermochromism of poly(di-n-alkyl)silane copolymers

A series of poly(di-n-alkyl)silane copolymers derived from Poly(di-n-hexyl)silane, PDHS, was prepared. Mesomorphic phase transitions of these copolymers depend on fraction as well as on the size of the comonomers. DSC and temperature dependent UV-spectroscopy were employed to study the effect of constitutional disorder on the length of all-trans σ-conjugated Si-Si catenated chromophores.

Gas-phase x-ray photoelectron spectroscopy of model molecules relating to the thermochromism in poly(3-alkylthiophene)

Previously, a geometrical model of the thermochromism in poly(3-alkylthiophene) was proposed, based upon an analysis of optical absorption spectra as well as ultraviolet and x-ray photoelectron spectra (UPS and XPS). In the present contribution, the shake-up features in the XPS C(1s) spectra of thiophene, hexyl-substituted thiophene, and bithiophene molecules in the gas phase, are compared with the shake-up features in previously published XPS C1s spectra of poly(3-hexylthiophene) and poly(3-butylthiophene). An analysis of these gas phase molecular data confirms the geometric model of electronic localization in the polymer materials proposed previously.

Thermochromism in poly(3-alkylthiophenes) and their polymer blends

We review the present understanding of the thermochromism found in the conjugated polymer poly(3-alkylthiophene) (P3AT). This phenomenon, a reversible change of colour of the polymer in the solid state with temperature, is analogous to the solvatochromism found in solutions of the polymer when varying the solvent quality by chemical composition or temperature. Thermochromism in polymer blends of P3AT with matrix polymers is reported, as well as electron microscopy of such blends. The results are discussed in the framework of phase segregation between the matrix polymer and the conductive polymer. Thermal undoping processes in the P3ATs and their polymer blends are briefly reviewed.

Structural study of thermochromism in poly(di-n-alkylgermanes) by Raman spectroscopy in the visible and near infrared

Etude d'oligogermanes et du poly(dihexylgermane) et discussion du role des groupes alkyl dans la transition thermochromique observee. Proposition de mecanisme pour la transition

Solid-state structures and thermochromism of poly(di-n-butylsilylene) and poly(di-n-pentylsilylene)

Conformation helicoidale 713 du squelette du PDBS et du PDPS avec une transition de phase du 1er ordre respectivement a 85 et 70 o C, au-dessus de laquelle la conformation est desordonnee mais qui ne s'accompagne pas de variation importante des spectres UV a l'etat solide. Deplacement bathochrome des spectres UV du PDBS et du PDPS en solution par refroidisssement. Discussion des differences entre spectres UV en solution et a l'etat solide

Thermochromism in poly(3-hexylthiophene) in the solid state: A spectroscopic study of temperature-dependent conformational defects

Reversible thermochromism in thin solid films of poly(3-hexylthiophene), or P3HT, has been studied using ultraviolet and x-ray photoelectron spectroscopies (UPS and XPS, respectively). The UPS and XPS spectra, as well as previously published optical absorption spectra, are analyzed using the results of valence effective Hamiltonian (VEH) quantum chemical calculations of the electronic structure of isolated polymer chains. The analysis of the spectra indicates that at elevated temperatures thermally induced electronic localization occurs as a consequence of thermally induced conformational disorder.