The exploration of two-dimensional (2D) sheets beyond graphene has been gaining increasing interest. In this work, using first-principles calculations combined with grand canonical Monte Carlo (GCMC) simulations we systematically study the stability, electronic structure, optical absorbance and hydrogen adsorption of porphyrin (Por)-based nanosheets. We find these sheets to be thermally and mechanically stable. In addition, their electronic structure can be tuned from semiconducting to metallic by doping different metal atoms, and the sheets can absorb near infrared (NIR) light. We also calculate the hydrogen storage capacities of the MPor (M = Mg, Ca, Sc) at 298 K and 100 bar pressure and find that the hydrogen gravimetric density of ScPor nanosheet can reach 6.71 wt% which represents an enhancement of 45% as compared to the Sc-phthalocyanine sheet. The present study provides new insight into 2D organic nanostructures with potential applications. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.