 [cm 7 The optical properties of 7-12[X] were investigated in diluted CH2Cl2 solutions (c = 5.10 -6 mol.L - 1 , Fig. , Fig. -16 and Table ). All derivatives display similar absorption spectra with a sharp absorption band between 419 nm and 468 nm with high extinction coefficients (70-135 000 L.mol - 1 .cm -1 ) and a clear shoulder. Such band topology is typical of cyanines in their IPS, in agreement with the structural observations (see above). As evidenced in Fig. , no aggregation occurred in diluted DCM, as expected due to the presence of the bulky P-atom. In addition, the absorption spectra are independent of the solvent (Fig. ). The absorption maxima are in the typical range of dimethylamino-substituted pentamethine (Cyanine A (Fig. , n =2): labs = 416 nm), showing that the presence of P does not affect the conjugation along the polymethine bridge. Surprisingly, the effect of substituents (either electron-donating -OMe or electron-withdrawing -F) on the phenyl