Synthesis and spectral properties of novel iminophosphoranes

Three new iminophosphoranes coded as FPZ1 (Ph–C≡C–C₆H₄–N = PPh₃), FPZ2 (Ph–N = P(C₆H₄–C≡C–Ph)₃) and FPZ3 (Ph–C≡C–C₆H₄–N = P(C₆H₄–C≡C–Ph)₃) were designed and synthesized by introducing different numbers of phenylene acetylene units to FPZ0 (Ph–N = PPh₃). The effect of structural modification was studied in detail analyzing the absorption spectra, the emission spectra, and the distributions of the electron density. The absorption spectra of the new iminophosphoranes are shown to be a linear combination of the spectra of each part by the artificial combinatorial absorption spectrum, which coincides with the real one. Most probably the individual parts can’t conjugate due to the tetrahedral structure. The probably formed excimer of FPZ0 and FPZ1 causes in their solid emission spectra an obvious bathochromic shift as compared to that of FPZ2 and FPZ3. The melting point data also showed that long branches of FPZ2 and FPZ3 will attenuate the interactions between the molecules. The results of quantum chemical calculations show that the electronic density in the HOMO of FPZ1, FPZ2, and FPZ3 is delocalized over the iminoaryl moieties. The electron density in the LUMO is delocalized over the triaryl phosphine moieties, but only concentrated on two branches, which directly determines the main direction of intramolecular charge transfer.