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

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 π–π 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 π–π 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.