meta-Terphenyl Phosphaalkenes Bearing Electron-Donating and -Accepting Groups

A set of para-substituted meta-terphenyl phosphaalkenes of the form 4-X-2,6-MeS(2)C(6)H(2)P=C(H)C(6)H(4)-4-X' (X = H, MeO or NMe(2); X' = H, CN, or NO(2)) have been synthesized to allow systematic studies of the impact of remote X and X' substituents on the phosphaalkene unit. The new compounds were characterized by (1)H and (31)P NMR spectroscopy, UV/Vis absorption spectroscopy, single X-ray crystal structures (for four compounds) and by electrochemical studies. The introduction of remote groups (X') on the less hindered phenyl ring generated more significant effects on the physical properties of the materials than did substituents (X) on the hindered meta-terphenyl rings. These effects were also explored by computational methods in order to assess the influence of substituents on structures and properties. The polarization of these molecules is less than that produced for analogous alkenes, as the phosphaalkenes bear sterically demanding groups that constrain the systems to adopt conformations that are less than ideal for maximum pi-conjugation of the central pi network