A new polymorph of zinc-phthalocyanine and its optical properties

Zinc-phthalocyanine has great potential for the applications in band-structure engineering, organic solar cells and photodynamic therapy. The optical and structural properties of zinc-phthalocyanine have been studied extensively previously. Here we report we have fabricated the nanowires of zinc-phthalocyanines (the eta-phase) and investigated their crystal structures and optical properties. The in-situ x-ray-diffraction experiments show that zinc-phthalocyanine nanowires grown at the low-temperature region have a distinct crystal structure as compared with the zinc-phthalocyanine polymorphs reported previously. We have also fitted the x-ray diffraction data and obtained the crystal-structure parameters, which further suggests that the nanowire phase has a new crystal structure. The UV-Vis experiments suggest similar qualitative feature in both the Q-band and the B-band, but slightly different quantitative perspectives. As explained by using the first-principles calculations, a mixture of intra-molecular and charge-transfer excitations can account for the splitting of the Q-band. Our work can provide a solid foundation for the further applications of zinc-phthalocyanines in organic optoelectronics.