Optical and Electrochemical Properties of Anthraquinone Imine Based Dyes for Dye-Sensitized Solar Cells

A number of anthraquinone imines (1-3, 5-8) and an anthrone diamine (4) have been synthesized by the condensation of 9,9-dimethoxy-10-anthrone derivatives (13, 18, and 23) with different primary aromatic amines and, in the case of benzoacridinone 7, by a subsequent photoinduced 6 pi electrocyclization. All the compounds were fully characterized by UV/Vis spectroscopy, cyclic voltammetry, and X-ray diffraction. The XRD analyses proved that the preferred tautomers of 1, 3, and 5 have the 9-amino-1,10-anthraquinone or 1-hydroxy-9,10-anthraquinone imine core. Furthermore, aminoanthraquinone 9 and phenoxazine 10 were synthesized by the reaction of 1-amino-9,10-anthraquinone with 3,5-di-tert-butylphenyl-o-benzoquinone, which led to dyes with high molar extinction coefficients of up to 101600 L mol(-1) cm(-1). In addition, the absorption maxima of the 1-hydroxy-9,10-anthraquinone imines appear in the range of 246 and 591 nm, at variance with the absorption maxima of the parent 1-hydroxy-9,10-anthraquinone. The cyclic voltammograms of all the compounds show multiple redox processes. In addition, the optical absorption and photoluminescence spectra of 3 show suppressed segregation on mesoporous TiO2 and an almost pure molecule photoluminescence spectrum containing two main transitions. A new excitonic transition was found in the crystal form.