The structures of derivatives 2-6[OTf]2 were all confirmed by single-crystal X-ray diffraction (Fig. ). In all compounds, the  4 , 4 -P atom shows a tetrahedral shape with usual valence angles and C-P bond lengths. In 2-5[OTf]2, the polyaromatic scaffold featuring the P-heterocycles is mainly planar (maximum deviation from the mean C-sp 2 plane, 0.32 Å), and the lateral phenyl rings lie perpendicularly to the main plane. The case of bisphosphaperylenium 6[OTf]2 is more peculiar as a significant -curvature is observed (maximum deviation from the mean C-sp 2 plane, 0.78 Å, Fig. ) due to steric hindrance between H and Ph at the bay position. This structural feature of the solid state pertains in solution according to DFT calculations (Fig. ). Finally, no intermolecular contact could be observed in the packing, which most likely results from the presence of bulky tetrahedral P-atoms, lateral exocyclic phenyl rings, and counterions. The spectroscopic properties of 2-6[OTf]2 are investigated in diluted CH2Cl2 solutions (c = 5.10 -6 mol.L -1 , Fig. and Table ). ). Interestingly, the P centers play a significant role in the transition in 2-5[OTf]2, whereas they do not seem to be involved in 6[OTf]2 (Fig. ). This is most likely related to the non-planar character of the -core of 6[OTf]2 , 15 and is in line with the specific NICS(0) value noted for the anti-aromatic P-rings (Fig. ). More generally, the NICS(0) calculation in this series nicely follow the Clar's sextet rule for polyaromatic compounds (Fig. ). All derivatives display fluorescence in solution. In this case, the emission wavelengths seem more affected by the molecular structure, as a 41 nm shift is observed between ). The PLQY in solid state are higher than in solution (11 %< < 39 %) with higher values for 2[OTf]2 (39%) and 3[OTf]2 (37%). This overall increase in PLQY is attributed to the restriction of rotations of the 8 lateral phenyl rotors that are present in each molecule, and to the presence of tetrahedral P-atom which prevent detrimental stacking, as confirmed by the crystallographic study. 16 ), suggesting the successive formation of a radical cation and a neutral specie. No oxidation waves are observed in these conditions. Interestingly, 2[OTf]2 displays a first reduction potential similar to MV[OTf]2 recorded in the same conditions (Fig. ). This clearly validates our design strategy to prepare multi-stage redox systems. The effect of the -core in the 2-6[OTf]2 series is rather strong with 6[OTf]2 having the less cathodic potential (Ered1(6[OTf]2) = -0.64 V vs Fc+/Fc) and 5[OTf]2 the more cathodic (Ered1(5[OTf]2) = -1.10 V vs Fc + /Fc) (Fig. ). This trend was already observed by Würthner et al. with comparable boron-doped PAHs. However, the presence of the charged P atoms To gain more insights into the reduced forms of these derivatives, spectroelectrochemical and EPR measurements were performed on 2[OTf]2, as representative compound. As illustrated Fig. , each redox state of 2[OTf]2 features characteristic UV-vis transitions.