catalysts Article Inversion of the Photogalvanic Effect of Conductive Polymers by Porphyrin Dopants Alexey A. Petrov, Daniil A. Lukyanov , Oleg A. Kopytko, Julia V. Novoselova, Elena V. Alekseeva and Oleg V. Levin *   Citation: Petrov, A.A.; Lukyanov, D.A.; Kopytko, O.A.; Novoselova, J.V.; Alekseeva, E.V.; Levin, O.V. Inversion of the Photogalvanic Effect of Conductive Polymers by Porphyrin Dopants. Catalysts 2021, 11, 729. https:// doi.org/10.3390/catal11060729 Academic Editor: Vincenzo Baglio Received: 15 May 2021 Accepted: 12 June 2021 Published: 12 June 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Institute of Chemistry, Saint Petersburg State University, University Embankment, 7/9, 199034 St. Petersburg, Russia; barmalei01@mail.ru (A.A.P.); lda93@yandex.ru (D.A.L.); kopytko2015@yandex.ru (O.A.K.); julivit.n@gmail.com (J.V.N.); alekseeva_ev@yahoo.com (E.V.A.) * Correspondence: o.levin@spbu.ru; Tel.: +7-812-4286900 Abstract: Conductive polymers are widely used as active and auxiliary materials for organic photo- voltaic cells due to their easily tunable properties, high electronic conductivity, and light absorption. Several conductive polymers show the cathodic photogalvanic effect in pristine state. Recently, photoelectrochemical oxygen reduction has been demonstrated for nickel complexes of Salen-type ligands. Herein, we report an unexpected inversion of the photogalvanic effect caused by doping of the NiSalen polymers with anionic porphyrins. The observed effect was studied by means of UV-Vis spectroscopy, cyclic voltammetry and chopped light chronoamperometry. While pristine NiSalens exhibit cathodic photopolarization, doping with porphyrins inverts the polarization. As a result, photoelectrochemical oxidation of the ascorbate proceeds smoothly on the NiSalen electrode doped with zinc porphyrins. The highest photocurrents were observed on NiSalen polymer with o-phenylene imine bridge, doped with anionic zinc porphyrin. Assuming this, porphyrin serves both as a catalytic center for the oxidation of ascorbate and an internal electron donor, facilitating the photoinduced charge transport and anodic depolarization. Keywords: photocurrent; NiSalen; porphyrin; electrodeposition; photovoltaics 1. Introduction Conductive polymers (CP) are a unique class of materials, which combine the benefits of organic materials and electronic conductors. Since their discovery, the CPs have been widely used not only as a replacement to inorganic conductors [1–3], but as advanced functional materials for electronics [4–6], electrochromic devices [6–9], sensing [10–12], and energy storage [13–18]. One of the main applications of the CPs is in photovoltaics, where they are used as donor phase [19–21] and hole transporting layer [22] materials in organic photovoltaic devices or counter electrode materials for dye-sensitized solar cells (DSSC) [23,24]. At the same time, an intrinsic photogalvanic effect is known for polythiophene CPs, which indicates the potential of these materials as active layers in DSSC-type architec- tures [25,26]. It was shown that the photocurrents of polythiophenes depended strongly on the nature of anionic dopant [27] and film morphology [28]. An increase of the photocur- rent was observed with increasing polymer orderliness and rigidity as well as decreasing dopant mobility [29]. Based on this knowledge, recently, the photogalvanic effect on highly rigid NiSalen-type conductive polymers has also been discovered [30] and implemented for the photoelectrochemical oxygen reaction reduction reaction (ORR) cell to produce hydrogen peroxide [31]. The electrochemical and optical properties of the CPs strongly depend on the nature of its anionic dopants, which may be illustrated by the comparison of commercial PE- DOT:PSS material and PEDOT doped with low molecular ions [32]. The effect of anion dopant is realized through the tuning of the polymer morphology [33] or ion diffusion Catalysts 2021, 11, 729. https://doi.org/10.3390/catal11060729 https://www.mdpi.com/journal/catalysts