Investigation of Perylene Photonic Wires by Combined Single-Molecule Fluorescence and Atomic Force Microscopy

Multichromophoric systems can exhibit interesting optical and electronic properties due to excitonic interactions between dye units that are near to each other. An exquisite example found in nature is the light-harvesting antenna system in photosynthetic bacteria, which allow for efficient light absorption and unidirectional transfer of energy to the reaction center during photosynthesis.The design of artificial multichromophoric arrays that mimic these properties is a great challenge, the ultimate goal being the construction of molecular photonic and electronic devices. A unique insight into the physical behavior of multichromophoric systems is obtained with the help of single-molecule-detection techniques. Single-molecule force microscopy not only provides information on the dimensions of the aggregates but also on the internal organization of the chromophores, a crucial issue that governs their excitonic behavior. Single-molecule optical spectroscopy reveals characteristic features arising from exciton coupling, such as single-emitter behavior and collective fluorescent/ nonfluorescent states, properties that otherwise remain hidden when probing the average behavior of ensembles of molecules. In this work we have combined force and optical microscopy to investigate at the single-molecule level the properties of a new class of rigid multichromophoric polymers intended to act as synthetic antennas.