At the molecular level, the cation always displays the cis geometry of the C1-C2 and C4-C5 (see and Fig. ). This result in a BLA in the crystalline state close to 0 (BLA < 0.019 Å, see Table ). Importantly, this absence of BLA is independent of the structure of the cation or of the counterion. DFT calculations performed in DCM provide bond distances that are close to the experimental values, the difference between measured and computed bond lengths being of the order of the impact of the counterion on the experimental data. Similarly, the P-C bond lengths are almost identical (1.733 Å <dP-C< 1.753 Å) and characteristic of a one and a half R3P-C bond, with again similar DFT values. The lack of BLA change when modifying the counterion is in marked contrast to the observations made on the polymethine cyanines. This can be attributed to the bulkiness of tetravalent P atoms which prevents significant interactions between the ions. Given the impact of the anion on heptamethine dyes optical properties, the fact that phospha-cyanine conserves its IPS irrespective of the counterion is of prime importance for further applications.