The presence of an electron-withdrawing P=O markdly impacts the redox properties. Compared to the purely hydrocarbon analogs, the cyclic voltammetry measurements revealed that 6-8 display monoelectronic quasi-reversible reduction waves at moderated potential (Ered-2.2V vs Fc, see Table and Fig. ). This redox behaviour arises from the presence of the electron-deficient phosphine oxide moiety directly attached to the PAH backbone. The optical properties (absorption/emission) of 5-8 have been investigated in diluted DCM solutions (c = 5.10 -6 mol.L - 1 , Fig. and Table ). The UV-vis absorption spectra of 5-8 are in marked contrast with those of their precursors 1-4. Indeed, they all display finely structured absorption bands in 300-440 nm range, characteristic for PAHs derivatives (Fig. ). Actually, the effect of the P-ring on the absorption is limited compared to the purely hydrocarbon analogues. As expected, the extension of the -backbone in the series leads to bathochromic shifts. TD-DFT calculations for 5 show satisfactory agreement with the experimental data (Table , Fig. ): the excitations have strong multi reference characters, e.g. the first excitation belong to a mixed HOMO-1 to LUMO and HOMO to LUMO+1 transitions. However, for compounds 6-8 various TD-DFT methods fail in describing the spectra, meaning that even the patterns cannot be properly simulated. Thus, ACD(2) calculations were applied, which not only predict a correct pattern, but also offer acceptable quantitative agreement (Table , Fig. ). Based on these data, the sets of low energy peaks with low intensities in the spectra of 5-8 belong to the vibrational fine structures of the lowest energy excitations. Again, the P-atom is practically not involved in any of these transitions. Importantly, however, the orbitals are not symmetric when compared to the C2v symmetric parent compounds without flanking phosphetene rings. As Fig. shows, the orbital contributions not only indicate asymmetric pattern along the linear chain, but also on the two sides of the quasi plane of the molecules. As it will be shown below, this will affect the chiroptical properties, because the asymmetries in the lobes differ among the different orbitals, offering a slight charge transfer character. The emission spectra also strongly differ from the precursors as finely structured emission bands with very low Stokes shifts are observed (Fig. and Table ). The lifetime is one order of magnitude higher compared to their precursors (10 ns, Table ), but remain in the range of purely fluorescent compounds. The luminescence is again highly similar to that of the purely hydrocarbonated analogs. The trend in emission wavelengths in the series agrees with that observed in absorption. These compounds all display high quantum yields (35-62%), in agreement with their rigid polyaromatic structures.