Acridinium derivatives are an important class of photocatalysts, where the interaction between the catalyst and the environment is under-reported. Here we show that the Lewis acidic acridinium salt exhibits various degrees of interactions with different Lewis bases, including water (HOH), methanol (CH3OH), tetrahydrofuran (THF, ROR), amines (R3N), and tert-butoxide (RO-) due to distinct physical properties stemming from different resonance forms. Interactions with water and methanol produce almost identical 1H NMR spectra but lead to drastically different UV absorption and luminescence emission, particularly phosphorescence; interactions with CH3OH/methanol and THF, which are differentiated by heat calorimetry titration, share the same luminescence spectra but show two different sets of 1H NMR peaks. These distinct physical properties could only be revealed by a combination of NMR and molecular fluorescence/phosphorescence spectroscopic methods. The current report serves as an example of using phosphorescence spectroscopy as a complementary tool for identifying interactions between organic molecules.