Covalently Functionalized Graphene Composites: Mechanistic Study of Interfacial Fluorescence Quenching and Recovery Processes

Abstract

Functionalized graphene oxide nanosheets (GONs) have received much attention in a broad range of applications from light harvesting devices to biological sensors. Owing to their implications in devices and sensors, the interactions between graphene and organic molecules, especially pi-pi interactions, have also been extensively investigated. Herein we present a mechanistic study of the interfacial fluorescence quenching and its recovery processes between a pyrene derivative, 1-(aminohexyl)-1-pyrenebutyricamide (4) as a fluorophore and nanometer-sized GO sheets. Owing to strong pi-pi interactions with 4, GON quenches the photoluminescence from pyrene in folded conformation of 4-GON. On the other hand, the treatment of 4-GON with sodium dodecyl sulfate (SDS) helps 4 overcome this strong pyrene/GON interactions and causes 4-GON to be in unfolded conformation where the fluorescence of pyrene is recovered. By time-resolved spectroscopy, the ultrafast energy and charge transfer behavior (<1 ps) is observed especially in folded conformation. In addition, photocurrent analysis under white light illumination leads us to distinguish electron transfer behavior in folded and unfolded conformation; effective charge separation occurs only in folded conformations, and photocurrents do as well. Overall, these findings provide fundamental understanding about the photophysics of pyrene functionalized GON nanostructures (4-GON) which could be utilized in nanosheet-electrode based sensors and light harvesting devices.