Photocurrent enhancements in a porphyrin-viologen linked compound under plasmonic and magnetic fields

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Zinc-porphyrin( ZnP )–viologen(V2+) linked compound containing six methylene group ( ZnP (6) V )–silver nanoparticle ( AgNP ) composite films was fabricated by combining electrostatic layer-by-layer adsorption and the Langmuir–Blodgett method. The incident photo to photocurrent efficiency (IPCE) values of the ZnP (6) V – AgNP composite films are higher than those of the ZnP (6) V films and much higher than those of ZnP derivative films without V2+moiety as a reference. The large increase in the IPCE values of the ZnP (6) V – AgNP composite films likely comes from a combination of localized surface plasmon resonance (LSPR) from AgNPs and photoinduced intramolecular electron-transfer upon linking to a V2+moiety. The photocurrents of the ZnP (6) V – AgNP composite films and the ZnP (6) V films increase upon application of a magnetic field. Magnetic field effects (MFEs) were clearly observed for both ZnP (6) V – AgNP composite films and the ZnP (6) V films. Photocurrents increase with magnetic field under low magnetic fields (B ≤ 150–300 mT) and are constant under high magnetic fields (B > 150–300 mT). MFEs can be explained by a radical pair mechanism. The magnitude of the MFEs in the ZnP (6) V – AgNP composite films is higher than that in the ZnP (6) V films. A remarkable increase in photocurrent for the ZnP (6) V – AgNP composite films was observed because of LSPR from the AgNPs in the presence of a magnetic field when compared with the ZnP (6) V films in the absence of a magnetic field.