Objectives
1. Synthesis and characterization of novel porphyrins and porphyrinoids; development of synthetic
tools for their efficient functionalization; exploration of their potential as
a) components for solar energy conversion devices,
b) model systems for heme enzymes to gain insight into mechanisms of dioxygen activation and other
small molecules,
c) photosensitizers in elaborate modular carrier systems for photodynamic therapy of tumors and
photodynamic inactivation of bacteria, fungi, molds, etc.
d) central parts of porphyrin-containing carbon-rich molecules and superstructures.
2. Synthesis and characterization of novel hexaphenylbenzene, hexabenzocoronenes and related
nanographenes;
development of synthetic tools for their efficient functionalization; exploration of their potential as
a) model systems for graphene to gain insight into charge and energy transport properties,
b) novel chiral carbon-based materials;
c) model systems for the controlled N-doping of graphene.
Scientific background
Porphyrins are ubiquitous dyes in nature which govern the most important transformations in living organism – making them aptly named “pigments of life”.
Their inherent photophysical, photochemical, and redox properties are likely responsible for their extensive appearance in Nature. In photosynthesis, porphyrins act as light harvesters in stunningly complex arrays, as electron donors in the reaction center and as electron transporting cofactors. In the respiratory chain, these cofactors play indispensable roles as dioxygen carriers, repositories and activators, the latter essentially delivering the “energy of life” in cytochrome c oxidase. It is not surprising that huge efforts are made to better understand these vital processes, because this may lead to improved artificial solar energy conversion in terms of light – energy – gathering and water splitting. As heme enzymes catalyze very important oxidations in nature, they are also in the focus of intense pharmaceutical research. Even without looking at Nature, porphyrins are fascinating molecules by themselves. They are able to form complexes with all metal ions, some half and even non-metals, often with several oxidation states available and strongly varying coordination geometries. Porphyrins act as sensitizer for singlet oxygen, thus are able to generate highly reactive species from dioxygen in the presence of light. This process, although detrimental in Nature, is used in the photodynamic therapy of tumors (PDT) as well as the photodynamic inactivation of germs. The highly polarizable π-electron system of porphyrins, their ability to either take-up or give-up two electrons in often reversible manner offers a high potential in molecular electronics. In contrast, nanographenes such as hexabenzocoronenes are more or less fully synthetic molecules. Given the fascinating properties of graphene, scientists around the world started to explore its potential in materials applications. A deeper understanding of carbon-rich materials can be obtained by looking at smaller parts or cut-outs of graphene, carbon nanotubes or fullerenes. Thus, hexabenzocoronenes have emerged as very useful model systems which are investigated by many groups worldwide.
