A 1, 3-dipolar cycloaddition protocol to porphyrin-functionalized reduced graphene oxide with a push-pull motif

Reduced graphene oxide (RGO) has been covalently functionalized with porphyrin moieties by two methods: A straightforward Prato reaction (i.e. a 1, 3-dipolar cycloaddition) with sarcosine and a formyl-containing porphyrin, and a stepwise method that involves a 1, 3-dipolar cycloaddition to the RGO surface using 4-hydroxybenzaldehyde, followed by nucleophilic substitution with an appropriate porphyrin. The chemical bonding of porphyrins to the RGO surface has been confirmed by ultraviolet/visible absorption, fluorescence, Fourier-transform infrared, and Raman spectroscopies, X-ray powder diffraction and X-ray photoelectron spectroscopy, transmission electron and atomic force microscopy, and thermogravimetric analysis; this chemical attachment assures efficient electron/energy transfer between RGO and the porphyrin, and affords improved optical nonlinearities compared to those of the RGO precursor and the pristine porphyrin.