Hole Mobility in Porphyrin- and Porphyrin-Fullerene Electropolymers

Abstract

Charge transport within films of several new types of electropolymerized porphyrin and porphyrin-fullerene dyad polymers was studied in order to obtain information on the suitability of these organic semiconductors for applications in solar energy conversion, sensor devices, etc. The films, prepared by electropolymerization on a conductive substrate, were immersed in acetonitrile and studied using chronocoulometric and cyclic voltammetric electrochemical methods. The charge diffusion coefficients were found to be dependent upon the electrolytic medium. Electrolyte anion size plays a significant role in determining the rate of migration of charge through the polymers, demonstrating that migration of positive charge is accompanied by migration of negative counterions. Bulkier anions markedly decrease the charge diffusion coefficient. This strong dependence suggests that anion mobility is the rate-limiting process for diffusional charge transport within the porphyrin polymer films and that the largest rates obtained are lower limits to the intrinsic cation mobility. With electrolytes containing the relatively small perchlorate anion, charge diffusion coefficients of the porphyrin polymers were similar to those reported for polyaniline under acidic conditions. The charge diffusion coefficient for a zinc porphyrin polymer was found to decrease 2 orders of magnitude in the presence of pyridine, suggesting that metal-containing porphyrins polymer films may have sensor applications. Cation (hole) mobilities previously reported in the literature for porphyrin-containing polymers with chemical structures quite different from those investigated here were much smaller than those found for the polymers in this study, but further investigation suggests that the differences are due to choice of electrode size and material.

Ethynylphenyl-Derivatized Free Base Porphyrins: Anodic Oxidation Processes and Covalent Grafting onto Glassy Carbon Electrodes

“…The nickel(II) porphyrin 8 was successfully attached as a monolayer to a platinum electrode by reduction of its meso-diazonium ion 16 . In contrast, direct anodic oxidation of the 3,5-dimethoxyphenyl group in H29 26 and the aniline group in H210 74 gave oligomers, apparently owing to coupling reactions at the mesocarbon (H) positions of the porphyrins. Although ethynyl/meso-carbon (H) coupling reactions are certainly possible in our monoethynyl systems, the observation that H22 shows facile multi-layering, whereas H23 does not, suggests that ethynyl/phenyl coupling is more facile in these systems.…”

“…It was generally observed that the square wave current for the second porphyrin oxidation was smaller than the first (Figure 10), a phenomenon reported previously for the two oxidations of surface-bound ethynylbis(fulvalene)diiron in [B(C6F5)4] --based electrolyte, and ascribed to mixed diffusivity of the large counter-anion at the solution/surface interface 73 . Brennan et al have also reported examples of overall decreased currents for porphyrin electropolymers in solutions containing large anions74 . In the present case, comparison with the behavior in smaller-anion electrolytes was not carried out owing to the complication of faster follow-up reactions of [H21] 2+ in smallanion media.…”

Porphyrin polymers and organic frameworks

“…Additionally, the rate of hole mobility diffusion was found to be strongly dependent on the electrolyte anion used in the analysis of the conductive polymer film. 103 An electropolymerized Zn or Pd tetra(p-hydroxyphenyl) porphyrin polymer was applied in a bulk heterojunction solar cell configuration and was composed of both donor and acceptor porphyrin layers ( Fig. 39(a)).…”

“…Conduction through the porphyrin film was proposed to be similar to that of the oxidative/reductive forms of polyaniline. Additionally, the rate of hole mobility diffusion was found to be strongly dependent on the electrolyte anion used in the analysis of the conductive polymer film …”

Synthesis and spectroscopic properties of a soluble semiconducting porphyrin polymer

“…Much of the research on conducting porphyrin polymers has been carried out by electropolymerization of porphyrin monomers to give semiconducting films on electrodes, [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] although some examples of solution chemical methods for formation of long porphyrin oligomers or polymers have been reported. [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] We have reported the electrochemical preparation and properties of polyporphyrins 32,33 and polyporphyrin-fullerene dyads 34 based on monomers featuring both a free meso-position and a meso-aminophenyl group. Electropolymerization generates semiconducting polymers in which porphyrin macrocycles are joined by aminophenyl linkers reminiscent of polyaniline.…”