Intrinsic dielectric properties of phthalocyanine crystals: An ab initio investigation

Cu phthalocyanine (CuPc) based composites are expected to display high dielectric constants, of the order of several hundreds, based on recent experimental work. In an attempt to determine whether CuPc has a high dielectric constant intrinsically, and if so, in order to identify the circumstances under which such high dielectric constants could result, a systematic ab initio study is undertaken. This study extends prior work on the intrinsic dielectric properties of isolated CuPc and the closely related ${\mathrm{H}}_{2}$ phthalocyanine $({\mathrm{H}}_{2}\mathrm{Pc})$ monomers. The tendency of CuPc and ${\mathrm{H}}_{2}\mathrm{Pc}$ monomers and polymeric sheets to stack is critically assessed, and the concomitant changes in the electronic and optical properties as a function of the stacking distance are determined. Our results indicate that both CuPc and ${\mathrm{H}}_{2}\mathrm{Pc}$ systems exhibit an insulator to metal transition as the stacking distance approaches $3\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$ (the equilibrium spacing). Consistent with this behavior, the dielectric constant reaches large values as the stacking distance approaches $3\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$, while it is small for larger stacking distances, in accord with our prior estimates.