Electron-accepting π-conjugated species with 1,8-naphthalic anhydride or diketophosphanyl units

Abstract

The synthesis and characterization of a series of 3- or 4-substituted 1,8-naphthalic anhydride compounds, and their organophosphorus analogues, bearing a cyclic diketophosphanyl moiety, are reported. The new anhydrides have been synthesized by Stille coupling with a variety of aryl groups with different donor strengths from the corresponding 3- and 4-bromo substituted anhydrides, respectively. The thienyl- and (dimethylamino)phenyl-substituted anhydrides have moreover been used as precursors for the synthesis of the corresponding diketophosphanyl derivatives by reaction with MesP(SiMe₃)₂. The photophysical and electrochemical properties of the new compounds have been studied. Density functional theory (DFT) and time-dependent DFT calculations have been carried out in order to rationalize their electronic structures and electronic absorption properties. The low-energy absorption bands exhibit mainly (π → π*) charge-transfer character from the aryl moieties to the anhydride or diketophosphanyl core, respectively. In the thiophene-containing diketophosphanyl compounds the low-energy absorption also shows some electron-transfer features from the phosphorus moiety (MesP) to the core. The charge-transfer nature of the transition has been confirmed by solvatochromic absorption and emission studies.