SYNTHESIS, SPECTROSCOPY, ELECTROCHEMISTRY, SPECTROELECTROCHEMISTRY, LANGMUIR-BLODGETT-FILM FORMATION, AND MOLECULAR-ORBITAL CALCULATIONS OFPLANAR BINUCLEAR PHTHALOCYANINES

A planar binuclear phthalocyanine and its dizinc and dicobalt derivati ves, in which two phthalocyanine units share a common benzene ring, ha ve been studied by spectroscopy, electrochemistry, and spectroelectroc hemistry. Their Langmuir-Blodgett film-farming properties have been ex amined, and the results of molecular orbital calculations on these and related systems are also presented. The properties are compared with those of the corresponding mononuclear control molecules. UV-visible-n ear IR absorption and magnetic circular dichroism spectroscopies and c yclic and differential pulse voltammetry indicate that, in these compo unds, two relatively independent chromophore units interact and theref ore that the two phthalocyanine planes are not completely planar in so lution. The electrochemical and spectroelectrochemical measurements sh ow the formations of various mixed-valence oxidation and reduction spe cies in the binuclear compounds. The nonmetalated and dizinc complexes exhibit both S-1 and S-2 emission. The radiative lifetimes (tau) of t he dizinc complex are smaller than those of the metal-free binuclear d erivative for both S-1 and S-2 emission, while the quantum yields (phi (F)) are larger. Furthermore, for S-2 emission, the phi(F) and tau val ues of the binuclear compounds are larger than those of the correspond ing mononuclear control molecules. Molecular orbital calculations with in the framework of the Pariser-Parr-Pople approximation reproduce the splitting of the Q absorption band and further show that the splittin g becomes larger the smaller the size of the shared common aromatic un it. In monolayers spread on water, the metal-free binuclear complex ap pears to have a slipped-stack conformation, tilted from the air-water interface normal plane. In Langmuir-Blodgett films, it may form a slip ped-stack molecular arrangement with the stacking axis parallel to the substrate and/or a flat-lying conformation on the substrate surface.