Limits of Exciton Delocalization in Molecular Aggregates
Exciton states of molecular aggregates, with a particular focus on delocalization length, are discussed. Despite the huge number of studies of molecular excitons, it is argued that there remain interesting open questions. It is hypothesized that limits for delocalization length are generally in range of tens to a hundred molecules, even at very low temperature. Effects that limit delocalization include: phase disorder from wave-zone electronic coupling, polarization fluctuations, and the extreme sensitivity of perfect delocalization to disorder as the size of the molecular aggregate increases. To gain physical insight, the inverse participation ratio is compared to the order parameter for a classical system of coupled, and hence entrained, oscillators—the Kuramoto model. Conclusions touch on limits of delocalization, quantum macroscopicity, and whether a quantum to classical transition can be identified.
- This article is part of the themed collection: Quantum effects in complex systems