The conversion of CO2 to synthetic fuels via photocatalysis represents a unique opportunity for sustainable energy production, addressing two of the most pressing problems of our time, namely climate change and the global energy crisis. In order to overcome the current constraints regarding performance for industrial applications, more efficient photocatalysts must be developed. In this thesis, I investigate the potential of emerging porous organic-based photocatalysts for CO2 photoreduction in the gas phase. The first part of my thesis focuses on better understanding the factors which govern charge transfer across semiconductor/metal-organic framework (MOF) heterojunction interfaces. By measuring the electronic structure of the individual heterojunction components and taking into account band bending, I built a band model of the heterojunction interface, which helped rationalize the photocatalytic enhancements and losses observed in MOF-based heterojunctions. This model highlights the importance of considering band bending when constructing MOF-based heterojunctions, an aspect that is not commonly investigated. The second part of my thesis focuses on investigating for the first time the ability of hypercrosslinked polymers (HCPs) to photoreduce CO2. I show that HCPs are promising visible-light active photocatalysts for the conversion of CO2 to CO. The leading HCP of this study outperforms TiO2 P25 by a factor of 7.5 when using only visible light and sacrificial H2O, without using additional sacrificial agents or co-catalysts. Lastly, the final part of my thesis focused on investigating the CO2 photoreduction mechanism, as well as the CO2 and H2O adsorption process on a triazine-biphenyl HCP. This was achieved by coupling in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), modulation excitation experiments, density functional theory (DFT) calculations, and advanced processing techniques. I found that CO2 and H2O adsorb on the same HCP sites albeit with different adsorption strengths. The primary amines of the triazines were identified as favouring strong CO2 binding interactions. No intermediate species were found under transient light irradiation. However, I observed partial CO2 and H2O desorption and a redistribution of interactions between the CO2/H2O molecules that remain adsorbed at the HCP adsorption sites. Overall, this thesis presents new opportunities for the use and rational design of emerging porous organic-based photocatalysts for CO2 reduction.