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The construction of a low-cost potentiostat and an electrochemical cell are described. Both have been used for the potentiostatic deposition of conducting polymers on FTO-coated glass. According to a reported procedure from literature an electrochromic window has been prepared and tested. Furthermore a novel window containing an additional electrodeposited polymer layer that shows a more pronounced electrochromism than the literature example is described for the first time. The required chemicals are inexpensive as well as the entire electrochemical equipment.
A series of novel arylene ladder polymers incorporating conjugated 1,5- and 2,6-naphthylene building blocks were synthesized. The polyketone ladder polymer precursors were prepared via a palladium-mediated Suzuki-type cross- coupling reaction using both conventional and microwave heating. While the 2,6-naphthylene polyketone precursor (2,6- NPK) was accessible from both heating protocols. the 1,5-naphthylene linked polyketones were only accessible via microwave-assisted (uW) procedures. and the polymer 1,5-NLP2 is the first example of a ladder polymer consisting exclusively of alternating six-membered rings prepared from this reaction sequence. The solution optical spectra of the final naphthylene ladder polymers exhibit the characteristic spectral shapes with a steep absorption edge and a vibronic fine structure common to fully rigidified ladder structures. The structural modification of the substitution pattern and the linkage positions at the naphthylene unit allows some tuning of the absorption and emission bands of the ladder polymers. The 2,6-naphthylene derivative exhibits an intense blue photoluminescence, while the two 1,5-naphthylene- linked ladder polymers exhibit a red shift of the 0-0 electronic transitions, leading to a blue-green photoluminescence
Persistent and transient hole-burning (HB) at 4.2 K have been applied to study the intrinsic properties of electronic excitations of a ladder type pi-conjugated poly(para-phenylene) in solutions. A narrow spectral hole less than I meV wide has been detected. The dependencies of the HB efficiency on the burn dose and wavelength, on doping the samples by electron scavenger are interpreted in terms of a photo reaction related to the two-level systems - specific low energy excitations in amorphous materials. In transient HB an additional hole broadening was observed which stems from the triplet energy transfer under conditions of lack of correlation of site energies of the singlet and triplet states of chromophores. (C) 2003 Elsevier B.V. All rights reserved
The effect of oxygen plasma treatment and/or silanization with hexamethyldisilazane (HMDS) on the surface chemistry and the morphology of the SiO2-gate insulator were studied with respect to the performance of organic field effect transistors. Using X-ray photoelectron spectroscopy (XPS), it is shown that silanization leads to the growth of a polysiloxane interfacial layer and that longer silanization times increase the thickness of this layer. Most important, silanization reduces the signal from surface contaminations such as oxidized hydrocarbon molecules. In fact, the lowest concentration of these contaminations was found after a combined oxygen plasma/silanization treatment. The results of these investigations were correlated with the characteristic device parameters of polymer field effect transistors with poly(3-hexylthiophene)s as the semiconducting layer. We found that the field effect mobility correlates with the concentration of contaminations as measured by XPS. We, finally, demonstrate that silanization significantly improves the operational stability of the device in air compared to the untreated devices
The electrical conductivity of organic semiconductors can be enhanced by orders of magnitude via doping with strong molecular electron acceptors or donors. Ground-state integer charge transfer and charge-transfer complex formation between organic semiconductors and molecular dopants have been suggested as the microscopic mechanisms causing these profound changes in electrical materials properties. Here, we study charge-transfer interactions between the common molecular p-dopant 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane and a systematic series of thiophene-based copolymers by a combination of spectroscopic techniques and electrical measurements. Subtle variations in chemical structure are seen to significantly impact the nature of the charge-transfer species and the efficiency of the doping process, underlining the need for a more detailed understanding of the microscopic doping mechanism in organic semiconductors to reliably guide targeted chemical design.
Energy transfer in a ladder-type methyl-poly(para-phenylene) doped by Pt(II)octaethylporphyrin
(2004)
The luminescence of a ladder-type methyl-poly(para-phenylene) (MeLPPP) doped by platinum-porphyrin dye PtOEP covering the concentration 10(-3) to 5% by weight has been measured employing cw and transient techniques. Upon excitating into the range of absorption of the host strong phosphorescence of the dopant is observed. Possible ways of populating of the dopant triplet state are considered. It is shown that the main channel is singlet-singlet energy transfer among chromophor groups of the polymer followed by Forster-type transfer to the guest and subsequent intersystem crossing. (C) 2003 Elsevier B.V. All rights reserved