Impact of inhomogeneities on optical and transport properties of molecular aggregates

The goal of my Ph.D. research is to investigate how structural features of objects which are composed of few thousand molecules, called molecular aggregates, affect their properties. This research has both fundamental relevance and technological applications. Fundamentally, the molecular aggregates are of just the right size to observe both quantum mechanical effects (because they are small enough) and collective effects (because they are large enough). This combination leads to their novel exotic properties which can be employed for various applications. One of their most interesting applications is as light-harvesting complexes in natural photosynthetic systems. For instance, green sulfur photosynthetic bacteria which are found at depths of 100 m in the Black Sea survive the scarce light condition by employing tubular molecular aggregates. These tubular molecular aggregates can absorb sunlight and transfer the absorbed energy with extremely high efficiency, such that almost all absorbed energy is delivered to the part where it is converted to chemical energy. This has inspired the synthesis of artificial mimics for application in artificial photosynthesis and photovoltaic applications. To accomplish such applications, we must understand how disorder or inhomogeneity in the structure, which is inevitable during their synthesis, impacts their properties and resulting functions. From our research, we learned how inhomogeneity in the orientation of the molecules and size of the molecular aggregates influence optical properties, as well as, how disorder in the energy of individual molecules impact the transfer of excitation energy. These insights contribute to realizing the light-harvesting applications of these molecular aggregates.