Comparative Charge Transfer Studies of Porphyrin-Fullerene Dyads: Substituents Effect.

Abstract

The present study deals with the study of charge transfer and photophysical properties of synthesized non-metallated fullerene-porphyrin dyad-III (H2P3-C60) via Prato reaction. The porphyrin has been substituted with electron donating groups (3,5-di-tert-butylbenzene) at meso positions facilitating the effective charge transfer for the formation of long lived charge-separated states in dyad molecule. The photophysical and thermal activated conducting properties of dyad was comprehensively studied to establish the effect of substituents and also by comparing with our reported dyad II having only meso-phenyl groups. The charge separation efficiency in dyad III has been calculated in solution as well as in films showing 62% and ˜99% quenching efficiency respectively suggesting faster photoinduced charge transfer from porphyrin to fullerene moiety. Transient absorption spectroscopy (TAS) showed formation of longer lived charge separated states in solution as well as in films compared to dyad-II. The thermal activated electrical conductivity measurement of dyad-III showed conductivity enhancement on increasing temperature. The activation energy for conduction was also found lower than dyad-II suggesting a substantial effect of electron-donating groups present on porphyrin ring in conducting behavior of dyad-III. Through this study with a very simple dyad structure we established that the presence of electron donating groups in dayds, highly influence photophysical and electronic properties. This special characteristic further makes them potential material to be used in various opto-electronic applications.