was used due to a limited solubility of AD in THF-d8 alone) are almost identical except for minor shifts from proton peaks on the AD ring. Specifically, when the solvent becomes more Lewis basic (more electron-donating from -CD3 or -CD2), the proton signals from the AD ring moves downfield while those from the benzyl ring remain unchanged. It is noted that the peak of the hydrogen atom on the acridinium ring para to the N atom appears unusually sensitive to the solvent change (from 9.96 ppm in D2O to 10.94 THF-d8). The more dramatic de-shielding is very likely a consequence of stronger hydrogen bonding between the THF-d8 oxygen lone pair and the aromatic proton para to the nitrogen, i.e., C-H…O, which decreases the H…O distance and depletes the electron density around the hydrogen atom, which stems the Pauli exclusion principle. Despite the minor differences observed for the 1 H-NMR spectra, the corresponding UV-Vis spectra in the three nondeuterated solvents (Figure ), particularly between H2O and THF, exhibit drastically differing patterns: in water, the lowest energy absorption extends to the visible region with well-defined vibronic structures (rendering the solution yellow to the naked eyes), attributed to the localized -* state of the acridinium ring. When the more electrondonating MeOH is used, the peak around ~415 nm is slightly weakened with a smeared vibronic feature, while a new shoulder band at ~285 nm emerges. For THF, however, the Up to this point, the hypothesis of nucleophilicity-induced de-aromatization still appears speculative based on a combination of NMR, UV-Vis and fluorescence spectra, given the possibility of reverse solvotochromic effect for charged organic molecules. The final piece of evidence arises from phosphorescence spectra, which were collected at a delay time of 1 ms (Figure ). The deep-red emission peaked at 645 nm with a shoulder around 700 nm is attributed to the triplet excited-state decay of the AD ring (with a calculated singlet-triplet energy gap, EST = 0.42 eV), which is consistent with previously published data and indicates unperturbed aromaticity in H2O. For ADBr in MeOH, while NMR, UV-Vis and steady-state fluorescence spectra also suggest very little structural or electronic state change compared to ADBr in water, the main phosphorescence emission with an emission maximum around 475 nm reveals that a significant portion of ADBr molecules are in a different electronic state, which also dominates the ADBr phosphorescence emission in THF (P = 481 nm, Figure ) at 77 K. Since both the emitting energy and vibronic spacing (1277 cm -1 ) in the fluorescence and phosphorescence spectra of ADBr in THF at 77 K bear good resemblance of DPA. If increased solvent nucleophilicity did induce DPA-like electronic structure for ADBr, one important question to ask is, whether THF forms a Lewis acid-base adduct (AD + …OR2) or covalent bond (AD-OR with ADBr?