Charge Carrier Dynamics and pH Effect on Optical Properties of Anionic and Cationic Porphyrin–Graphene Oxide Composites O. BAJJOU, 1,2,3 A. BAKOUR , 1,6,7 M. KHENFOUCH, 2,3 M. BAITOUL, 1 B. MOTHUDI, 2 M. MAAZA, 4,5 and E. FAULQUES 6 1.—University Sidi Mohamed Ben Abdellah, Faculty of Sciences, Dhar El Mahraz, Laboratory of Solid State Physics, Group of Polymers and Nanomaterials, PO Box 1796, Atlas, 30000 Fez, Morocco. 2.—Physics Department, College of Science, Engineering and Technology Science Campus, Corner of Christiaan de Wet Road and Pioneer Avenue, Florida, Johannesburg 1709, South Africa. 3.—Physics Department, CSET, Africa Graphene Center, University of South Africa, Florida Campus, Johannesburg 1710, South Africa. 4.—iThemba LABS-National Research Foundation of South Africa, Old Faure Road, PO Box 722, Somerset West, Western Cape Province 7129, South Africa. 5.—UNISA Africa Chair in Nanosciences-Nanotechnology, College of Graduate Studies, University of South Africa, Muckleneuk Ridge, PO Box 392, Pretoria, South Africa. 6.—Institut des Mate ´ riaux Jean Rouxel, Universite ´ de Nantes, CNRS, UMR 6502, 2 rue de la Houssinie `re, PO Box 3229, 44322 Nantes Cedex, France. 7.—e-mail: bakour.anass@gmail.com Composites of graphene oxide (GO) functionalized with Sn(V) tetrakis (4-pyridyl)porphyrin (SnTPyP 2+ ) and meso-tetrakis(4-phenylsulfonic acid)- porphyrin (H 4 TPPS 4 2À ) were prepared at different pH values.Successful syn- thesis of water-soluble stable suspension of GO–SnTPyP 2+ and GO–H 4 TPPS 4 2À was confirmed using various spectroscopic techniques, including scanning electronic microscopy (SEM), Raman spectroscopy, and ultraviolet–visible (UV–Vis) absorption. Variation of the pH was found to strongly influence the optical properties of the GO–SnTPyP 2+ and GO–H 4 TPPS 4 2À composites, as demonstrated by the UV–Vis absorption results. Steady-state photolumines- cence (PL) and time-resolved PL (TRPL) results for both composites showed PL quenching and decrease in the exciton mean lifetime, suggesting strong excited-state interactions between the different components. Moreover, charge carrier dynamics study revealed that insertion of GO into both porphyrin derivatives led to faster mean lifetime for excitons with a slight advantage in the case of the cationic porphyrin–GO composite, making it a better choice for charge separation applications thanks to the higher efficiency of charge/en- ergy transfer interactions. Key words: Graphene oxide, porphyrin precursors, Raman, UV–Vis absorption, time-resolved photoluminescence INTRODUCTION Graphene, a single plane of graphitic carbon, 1 has attracted an unprecedented wave of interest in the materials community thanks to its exceptional physical properties, 2 enabling its potential applica- tion in next-generation electronics, such as nanocomposites, 3–5 solar cells, transparent elec- trodes, and supercapacitors. 6 To date, graphene materials have generally been synthesized using various main methods such as mechanical exfoliation, epitaxial growth by chem- ical vapor deposition (CVD, representing one of the most promising approaches to obtain high- quality graphene), 7,8 chemical oxidation–reduc- tion, 9,10 arc discharge of graphite, epitaxial growth on SiC, and thermal fusion. However, perfect synthesis of GO in an ecoefficient method remains a challenge. 11 (Received June 25, 2017; accepted February 9, 2018) Journal of ELECTRONIC MATERIALS https://doi.org/10.1007/s11664-018-6139-3 Ó 2018 The Minerals, Metals & Materials Society