In a first set of experiments, we collected UV-Vis spectra of PTI-LiBr suspended in water at different concentrations of HCl (Figure ). Without HCl we observe the absorption of the lithium defect states at around 370 nm and the broad absorption of the conjugated PTI-backbone at around 290 nm. By increasing the H3O + concentration, two effects can be identified. Our first principles calculations predict that the triazine protonated structure is more stable than the imide bridge protonated structure. Based on this finding, we assume that the triazine protonation is prevalent. The calculated optical absorption spectra of the protonated materials (Figure ) indicate an overall red-shift of the absorption peaks in comparison with PTI-IF. This result is qualitatively in agreement with earlier predictions on analogous model systems. Specifically the red shift of the main peak in combination with the emergence of a second absorption band in the absorption spectrum of triazine protonated PTI (Figure , ii) is considered an effect of the symmetry breaking of the backbone structure upon protonation. The presence of two absorption bands in the system is in good agreement with two corresponding PLE maxima at 260 nm and 297 nm of the emission at 330 nm (Figure and 3e) present in dispersions with HCl concentrations larger than 10 -5 M at 260 nm and 300 nm (Figure and). It is noteworthy, that for excitation at 300 nm in dispersions at 10 - 2 M HCl the quantum yield obtained was 10% and for excitation at 370 nm 9%. The emission of the neutral dispersion at 486 nm is comparatively low with a quantum yield of 1% and no emission for excitation at 300 nm. The increased quantum yield is accompanied by an increase in lifetime (neutral 1 = 0.5 ns ±0.03 ns, 2 = 3.6 ns ±0.13 ns, pH1 1 = 1 ns ±0.05 ns, 2 = 4 ns ±0.10 ns). As typical for CN materials a two exponential fit was applied. The increase in quantum yield and lifetime is attributed to partial exfoliation of the layered PTI structure and, hence, reduced π-π stacking. Charging of PTI layers by reduction with sodium naphthalide and stabilization by derivatisation with an C12 alkane was described in literature. A route via protonation could be a viable alternative.