This thesis addresses the fundamental aspects of controlling transport through organic molecules by presenting a series of studies in the electronic properties of molecular junctions. The exploration and understanding of the electronic characteristics of single molecules connected to electrodes is an essential part in the application of electronics. Here, I implemented transport calculations based on the Landauer formula combined with Kohn–Sham orbitals extracted from density functional theory (DFT). Chapter 4 elucidates the validity of a ‘curly arrow rule’, which has been used widely by chemists and physicists to predict the electronic properties of molecular junctions. Anthraquinone is found to break this rule in the case of meta connectivity to electrodes. This is significant, because changing the redox state of meta-connected dihydroxyanthracene to meta-connected anthraquinone, increases the conductance by a couple of orders of magnitude, due to the transition from constructive to destructive QI, which can help in the design of the QI based single-molecule switches such as data storage elements. Finally, chapter 5 presents a theoretical investigation of electron transport through dimethyldihydropyrene (DHP) and Cyclophanediene (CPD) systems focusses on changes in the conductance as a consequence of photochemical stimuli. These molecules could be exploited in the function of electronic devices, when responding to external stimuli