Ultrafast Optical Dynamics of Metal-Free and Cobalt Phthalocyanine Thin Films

We discuss the structural properties and the ultrafast dynamics of absorption changes of cobalt phthalocyanine (Pc) thin films (CoPc), and we compare them to metal-free H2Pc. We find that both types of films are polycrystalline and have orthorhombic alpha-polymorph structure. The absorption relaxation dynamics of H2Pc reveals a slow process on the tenths of picoseconds (ps) time scale and a very slow process with recovery time of hundreds of ps. We show that the increasing relaxation rate is not due to exciton-exciton scattering; it is the presence of Co atoms that leads to the Much faster dynamics.