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