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

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.