Exciton Transport in Molecular Aggregates – From Natural Antennas to Synthetic Chromophore Systems

Abstract

The transport of excitation energy in molecular aggregates is of crucial importance for the function of organic optoelectronic devices and next‐generation solar cells. First, this review summarizes the theoretical background of the nature of the electronically excited states of molecular aggregates. For these systems, the electronic interaction between the monomers leads to the formation of exciton states. This goes along with a shift of the excitation energies and a redistribution of the oscillator strength with respect to the monomers. Next, a brief overview is provided over experimental techniques that allow to study the properties of excitons in molecular aggregates. This includes single‐molecule spectroscopy, coherent two‐dimensional (2D) spectroscopy, and single‐molecule coherent spectroscopy. Finally, examples of molecular aggregates spanning the range from natural systems that act in photosynthesis as light‐harvesting antennas to artificial aggregates built from synthetic chromophores are illustrated.

Fluorescent J-aggregates of cyanine dyes: basic research and applications review

“…In photosynthetic organisms the solar light is absorbed by the aggregate of antenna pigments and then funnelled to the reaction center for employing in a chemical reaction. The search for artificial antenna systems where the capture of the energy of light could optimally take place is of great interest [23], and the J-aggregates are expected to be highly efficient as such optical antennas [30]. Being able for energy collection and delivery they can be useful for modeling the processes occurring in natural photosynthesis [215].…”

Self‐Assembly of Bowl‐Shaped Naphthalimide‐Annulated Corannulene

“…Similar as for PBI 4 , the longer lifetime is characteristic for a partially forbidden radiative process, presumably from an excimer‐like excited state. This view is also corroborated by the absorption spectra of dimer 3 a which show a decrease of the intensity of the 0,0 transition and a hypsochromic shift of the absorption maximum compared to the monomer which are indicative for a H‐type exciton coupling …”

Enhanced Energy Transfer in Doped Bifluorene Single Crystals: Prospects for Organic Lasers

“…It is important to point out, that an apparent exciton hopping time of 6 × 10 −14 s estimated from quenching experiments is faster than 10 −13 –10 −12 s predicted for other doped organic crystals . Within such ultrafast timescales the incoherent exciton hopping model becomes inaccurate to describe energy transport, hence partly coherent exciton motion must be considered . Evolution of initially delocalized excitons into hopping motion is governed by scattering due to static and dynamic (thermal) disorder, which limit coherence size .…”