Luminescent Mannich bases: Synthesis, crystal structures, and photophysical properties

•Three Mannich bases have been obtained from 5‑bromo-salicylaldehyde.•The crystal structures of one out of the three Mannich bases have been solved.•The UV–Vis absorption and emission spectra were investigated in different solvents.•Various species have been identified in solution: neutral, zwitterionic, anionic, and cationic.•The experimental results were rationalized by DFT and TD-DFT calculations. Three Mannich bases have been obtained starting from 5‑bromo-salicylaldehyde: 5‑bromo-3-(((2-(dimethylamino)ethyl)(methyl)amino)methyl)-2-hydroxybenzaldehyde (TMEN), 5‑bromo-3-((benzyl(methyl)amino)methyl)-2-hydroxybenzaldehyde (MBA), 5‑bromo-3-(ethyl(methyl)amino)methyl)-2-hydroxybenzaldehyde (EMA). The crystal structure of MBA has been solved. The UV–Vis absorption and emission spectra were investigated in different solvents, revealing the presence of several species, the neutral forms, the zwitterionic, the anionic and the cationic (the protonated nitrogen) ones. In order to characterize the last two species, further experiments were performed in the presence of hydrogen extracting and hydrogen donating compounds, sodium fluoride (NaF) and tetrabutylammonium hydroxide (TBOH) to evidence the anion, and trichloroacetic acid (TCA) for the protonated cation. The experimental results were rationalized by DFT calculations of the potential energy surfaces (PES) of the S0 and S1 states and of the absorption and emission maxima. The luminescence properties of three Mannich bases have been investigated and rationalized by DFT and TD-DFT calculations. [Display omitted]