Ahmet M. Önal

A blue to highly transmissive soluble electrochromic polymer based on poly(3,4-propylenedioxyselenophene) with a high stability and coloration efficiency

The optical and electrochemical properties of a regioregular and soluble alkylenedioxyselenophene-based electrochromic polymer, namely poly(3,3-didecyl-3,4-dihydro-2H-selenopheno[3,4-b][1,4]dioxepine (PProDOS-C10), which is synthesized by electrochemical polymerization, are highlighted. It is noted that this unique polymer has a low band gap (1.58 eV) and is exceptionally stable under ambient atmospheric conditions. Polymer films retain 97% of their electroactivity after 40 000 cycles. The percentage transmittance of a PProDOS-C10 film was found to be 56.4% at 638 nm and 55.8% at 700 nm. Furthermore, this novel soluble PProDOS-C10polymer shows an electrochromic behavior: a color change from pure blue to a highly transparent state in a low switching time (1.0 s) during oxidation, with high coloration efficiencies (328 cm2C−1 at 638 nm and 319 cm2C−1 at 700 nm) when compared to its thiophene analogue.

Electrochemical polymerization of furan and 2-methylfuran

Abstract Conductive polyfuran and poly(2-methyl)furan are prepared by controlled potential electrolysis in acetonitrile at room temperature. It is found that conductivity of polyfuran decreased by factor of 4 when methyl group is present in the α position. Temperature effect on the rate of polymerization of furan is studied by cyclic voltammetry technique and an increase in the initial rate of polymerization was observed with increasing temperature. Apparent activation energy of electrochemical polymerization of furan was found to be 7.5 kJ/mole. The mechanism of electrochemical polymerization was investigated by in situ ESR.

Free radical mediated interaction of ascorbic acid and ascorbate/Cu(II) with viral and plasmid DNAs

Previous studies indicate that ascorbic acid, when combined with copper or iron cleaves several viral DNA. ln this study, we generated the ascorbate radical anion electrochemically in a simple chemical environment without the participation of a metal ion. This solution possesses viral DNA scission activity. Ohe absence of catalytic metal ions [Fe (III) and Cu(II)] in the incubation medium was evidenced by metal chelating agents such as desferrioxamine and EDTA. Ohe radical quenching at high EDTA concentration was attributed to ionic strength of EDTA rather than metal chelation. Ohe effects of antioxidants, radical scavangers, catalase, superoxide dismutase and some proteins on DNA cleavage have been tested. Cleavage may not arise directly from ascorbate free radical but the reaction of the radical form of ascorbate with oxygen may produce the actual reactive species. Aerobic oxidation of ascorbate itself strictly requires transition metal catalysts, however electrochemically produced ascorbyl radical avoided the kinetic barrier that prevented direct oxidation of ascorbic acid with oxygen and eliminated the need for the transition metal ion catalysts.

Pyrolysis mass spectrometry analysis of BF4- doped polythiophene

Abstract Pyrolysis of electrochemically prepared BF4 − doped polythiophene (PTh) by direct insertion probe and Currie point pyrolysis gas chromatography mass spectrometry techniques indicated that thermal decomposition of PTh occurs in two steps. In accordance with literature results, the first step is assigned to the loss of the dopant, and the second step to the degradation of the polymer backbone producing segments of various conjugation lengths. At elevated temperatures, detection of products such as H2S and C2H2 indicating cleavage of the thiophene (Th) ring was associated with a network structure. For the dedoped samples, a significant increase in the relative intensities of the peaks characteristic to the counter ion of the dopant, N(C4H9)4 + pointed out the inward diffusion of (C4H9)4N+ during the dedoping process.

Characterization of BF4- doped polythiophene via pyrolysis mass spectrometry

In this work, electrochemically polymerizated polythiophene have been characterized by direct pyrolysis MS and Curie point pyrolysis GCMS techniques. The effect of doping level, and type of the dopant on thermal characteristics and decomposition products of polythiophene have been investigated. It has been determined that the thermal degradation of polythiophene occurs in two steps, the first being the loss of the dopant, and the second being the degradation of the polymer main chain. The temperature range at which the loss of dopant observed depends on the type of the dopant. However, thermal degradation of the polythiophene chains does not depend on the type of the dopant used.

Electrochemical and quantum chemical studies on mitomycin and adriamycin

In-situ spectroelectrochemical redox behaviour of two prominent chemotherapeutic agents, mitomycin and adriamycin were studied at constant potential. AM1 (UHF) type quantum chemical calculations on the neutral as well as radical anion and cation forms of mitomycin and adriamycin were performed.

ESR and conductivity investigations on electrochemically synthesized polyfuran and polythiophene

Abstract ESR studies have been carried out on ClO 4 − -doped polyfuran (PF) and BF 4 − -doped polythiophene (PT) films synthesized by constant potential electrolysis. Variation of spin concentration and linewidth of ESR signal with temperature were investigated. The temperature dependence of conductivity supported the Motts variable range hopping mechanism for PT and PF freestanding films. Temperature dependence of activation energy indicated that hopping is the dominating mechanism of charge transport.

Synthesis and electrochemical polymerization of diketopyrrolopyrrole based donor–acceptor–donor monomers containing 3,6- and 2,7-linked carbazoles

Three new donor–acceptor–donor (D–A–D) type monomers bearing 2,7- or 3,6-linked carbazoles as the donor unit and 2,5-dihydro-3,6-di-2-thienyl-pyrrolo[3,4-c]pyrrole-1,4-dione (DPP) as the electron poor acceptor unit were synthesized via a Suzuki cross coupling reaction. The monomers were electrochemically polymerized both by repetitive cycling and by constant potential electrolysis in acetonitrile–tetrabutylammonium hexafluorophosphate electrolytic medium containing boron trifluoride diethyl etherate (BFEE). Optical and electrochemical properties of the monomers and their corresponding polymers were investigated and it was found that optical properties show slight variations depending on both the substituent on the nitrogen atom and the linkage site. Monomers, besides reversible oxidations and reversible reduction peaks similar to those present in the differential pulse voltammogram of the acceptor unit, exhibit one irreversible oxidation peak responsible for initiating the electrochemical polymerization of the monomers. Both electrochemical and optical data were used to elucidate the band gap (Eg) values of the polymers and it was found that polymer films obtained from 3,6-linked carbazole derivatives have slightly lower Eg values compared to 2,7-linked derivatives. Furthermore, based on the observed electrochemical behavior of the monomers, a possible mechanism for the electrochemical oxidation was proposed.

Radiation-induced and electroinitiated polymerization of allylbenzene

Abstract Radiation-induced and electroinitiated polymerization of allylbenzene has been investigated. Radiation-induced polymerization at room temperature was found to give mainly dimers and trimers with a maximum yield of 5%. Electroinitiated polymerization of the monomer yielded insoluble polymer films on the surface of the anode together with low molecular weight polymers in the bulk solution. The effects of temperature and monomer concentration on the rate of electroinitiated polymerization were also studied. The decrease in monomer concentration during electroinitiated polymerization was studied by taking cyclic voltammograms of the electrolysis solution. An apparent activation energy of 5.5 kJ mol −1 was found for the electroinitiated polymerization. The polymers were characterized by taking infra-red and nuclear magnetic resonance spectra. The polymerization proceeds via double bond addition of monomer together with isomerization of allylbenzene into β-methylstyrene.

Investigation of the effect of dopant on characteristics of poly(3-methyl thiophene) via pyrolysis mass spectrometry

In this work, a direct insertion probe pyrolysis mass spectrometry technique was applied to investigate the thermal and the structural characteristics of electrochemically prepared PF6 − and BF4 − doped poly(3‐methylthiophene) (PMTh) to explore the effect of dopant on thermal and structural characteristics. It has been determined that the thermal degradation of PMTh occurs in two steps as in the case of polythiophene, (PTh). The first step was assigned to the loss of the dopant, and the second step to the degradation of the polymer backbone producing segments of various conjugation lengths. Generation of some oligomers occurred at lower temperatures for PF6 − doped films compared to BF4‐PMTh. On the other hand for both PMTh samples products due to the degradation of thiophene ring were detected in the same temperature range. Evolution of dopant based products occurred in a broad temperature range for both PF6 − and BF4 − doped poly(3‐methylthiophene). Reactions of dopants with H2O and polymer were very effective, especially for PF6 − and substitution of thiophene ring was noted for both samples. Decomposition of the polymer and inward diffusion of counter ion during dedoping processes of both polymers pointed out that electrochemical reversibility of the transition between the doped and undoped states is limited for PMTh.