To access information about the prevalent bond types and therefore the degree of condensation as well as possible defects, we conducted FT-IR spectroscopy on the products (Figure ). FT-IR spectra of the high-temperature products at 600 °C show a broad peak around 3300 cm -1 in addition to two discernible NH signals (at 3328 and 3217 cm -1 ). The latter are argued to originate from splitting of the imide N-H bond by partial conversion into N-Li. The broad feature is absent in the product obtained at 550 °C. The sharp band around 810 cm -1 is attributed to the out of plane bending mode of the six-membered triazine (C3N3) ring and is present in all samples. Likewise, the material obtained at low temperature has a clearer separation of bands in the CN stretching region 990-1600 cm -1 . There are two valid explanations for these observations: (i) the broad feature around 3300 cm -1 can be attributed to OH groups attached to the carbonaceous contaminants that are produced at elevated temperatures, and (ii) decreased band separation is indicative of structural disorder in the material obtained at high temperature as a consequence of thermal decomposition. The spectra of samples condensed at 600 °C for 72 h resemble those of amorphous CNH-compounds with the dominant infra-red absorption between 1600 and 1300 cm -1 from C-N modes and ring species. PXRD patterns confirm the transition of crystalline PTI-LiBr into a disordered material at long reaction times and 600 °C (Figure ). Condensation at 550 °C results in a slight shift in the diffraction pattern towards lower angles corresponding to an increase in plane distances. A conceivable reason is an increased ion loading in the structure obtained at reduced temperature. The same trend of higher product quality at the lower reaction temperature was also found by ssNMR. The C 13 spectrum shows the three carbon signals also observed in PTI-LiCl at =167.0 ppm 162.0 ppm and 158.0 ppm (Figure ). The bands show increased sharpness in the product condensed at 550 °C. We examined the sample morphologies by SEM (Figure ).The morphology of PTI-MX is described as hexagonal platelets and prisms with a basal cross-section of 100-500 nm in literature. Further decrease of the reaction temperature to 525 °C resulted in a product with additional PXRD peaks that could not be attributed to a PTI-type material and, hence, the material was not investigated further (Figure ). We selected the PTI-LiBr sample obtained at 550 °C (48 h) for further optoelectronic experiments based on its structure and composition. The decreased carbon contamination allows us to measure UV-Vis of PTI-LiBr dispersions (Figure , blue plot). We find two broad features around 370 and 290 nm. The state at 370 nm can be excited yielding the photoluminescence spectrum shown in Figure (blue plot). The photoluminescence excitation spectrum shows a single maximum at 486 nm (Figure , blue line). This emissive state is a result of the replacement of hydrogen with lithium at triazine bridging N-H units. This defect reduces the conduction band minimum energy accounting for the contraction of the optical gap of this structure. Exciting PTI-LiBr at around 290 nm does not yield a new emission band and decreases the emission at 486 nm drastically (c.f. Figure ). Hence, the state that belongs to the absorption at 290 nm in PTI-LiBr is quenched. To gain a better understanding of these two states, we prepared an intercalation free PTI (PTI-IF) comprised only of the CNbackbone (SI Experimental). PXRD, FT-IR and UV-Raman of PTI-IF are depicted in Figure . Removal of the coordinating lithium and bromine ions leads to disorder as can be found comparing the PXRD spectra of PTI-IF to PTI-LiBr. The width of the reflexes is broadened and some peaks are deleted entirely. Comparing FT-IR spectra of PTI-LiBr and PTI-IF we find better band separation in the ion free PTI-IF as was observed by Suter et al. UV-Raman spectra with a 266 nm excitation source reveal the and 685 cm -1 (weak) in PTI-IF. Broad contributions in both samples at 1300 cm -1 (broad, weak) and 1630 cm -1 (strong) can be assigned to the so called D and G bands due to breathing modes in sp 2 bonded rings and CN sp 2 bond stretching in rings and chains respectively. The presence of a sharp, strong Raman band at 1088 cm -1 in PTI-LiBr samples indicates a carbonate species. The lithium defect can undergo hydrolysis to form LiOH in presence of water. This is the known reason for the basic character of PTI-MX in water as reported in literature. LiOH is a known CO2 absorber. We propose that under environmental conditions (in presence of water and CO2) LiOH can form at the surface of the crystallites which in turn can absorb CO2 leading to the presence of lithium carbonate species. Hence, in PTI-IF this Raman band is absent. Optical characterization by UV-Vis spectroscopy reveals that by removing most of the ions in the structure, we lose the absorption band at 370 nm, as expected, since this state is the result of Lidefects. Absorption at 290 nm is still prevalent and, hence, it is assigned to the PTI-conjugated backbone. This observation matches well with the theoretical predictions for an intercalation free PTI (see Figure ). The result of this calculation shows that PTI-IF layers have a single bright absorption band at around 320 nm, in good agreement with the experimental results, considering the necessary simplifications applied to the model structure adopted in the simulation (see Figure ,S8) The absence of emission from the 290 nm state in PTI-LiBr could be due to the presence of the Li defects acting as a deep trap. Excitons formed in the organic backbone will recombine primarily at these energetically favorable defect sites. A similar effect can be observed for keto-defects in polyfluorene backbones. It is not possible to determine the quantum yield of PTI samples obtained at 600 °C because of strong absorption from the accompanying carbon-rich phase. The quantum yield of films cast from the 550 °C product equals 0.4%. Optical images comparing products obtained at 550 °C and 600 °C illuminated with a 375 nm LED can be accessed in the SI (Figure ).