Computational methods. All calculations were performed using the Gaussian 16 software package with resources of the Laboratory Computing Resource Center at Argonne National Laboratory. Geometry and frequency optimizations were performed at the B3LYP/6-31+g(d,p) level of theory and LANL2DZ ECP basis set for Ru center. with integral equation formalism variant of polarizable continuum model (iefpcm) for solvation effects. Frequency calculations confirmed the structures obtained were at the local minima of their potential energy surfaces by resulting in the absence of imaginary frequencies. TD-DFT was performed to predict the spectra of Ru-bpm, Ru-bpmH + , and Ru-bpmH2 . DFT-based difference density calculations were performed to visualize the movement of charge on the molecule during the lowest energy, allowed transition. Natural transition orbitals and charge transfer matrices 32 that were generated to better understand the nature of transitions in the UV-vis spectrum. To quantify charge transfer characters in a transition, we grouped the atoms in the molecule into four fragments: Ru, terpy, bpm and H2O. The charge transfer matrix elements are computed as a probability of each electronic state involved in the charge transfer event between fragments.