Charge transfer in organic fluorophores is a fundamental photophysical process that can be either beneficial, e.g., facilitating thermally activated delayed fluorescence, or detrimental, e.g., mediating emission quenching. It has been previously shown that both protonation and N-alkylation of quinoline containing compounds allows straightforward synthetic control of the charge transfer, emission energy and photoluminescence quantum yield (PLQY) (Scheme 1a), with the effect of alkylation mirroring those of protonation while being necessarily more permanent. Control of photoluminescence and photophysical properties in organic molecules has significant appeal for a range of applications from organic light-emitting diodes (OLEDs) to biological imaging and sensing. Given the importance of the charge transfer (CT) process in influencing key photophysical parameters developing structure-activity relationships (SARs) to describe CT formation will be of interest to a wide range of stakeholders. In medicinal chemistry the development of SARs is standard practice, but a similarly detailed understanding of the structural properties controlling charge transfer has yet to be fully developed. Since protonation and N-alkylation have a significant and predictable effect on CT states in quinoline-containing compounds these provide a good starting point for exploring these vital fundamental processes and developing effective SARs.