Web Release Date: February 20,
Strongly Coupled Excitonic States in H-Aggregated Single Crystalline Nanoparticles of 2,5-Bis(4-methoxybenzylidene) Cyclopentanone
and
Key Laboratory of Biomimetic Sensing and Advanced Robot Technology, Institute of Intelligent Machines, Chinese Academy of Sciences, Hefei, Anhui 230031, China, and Department of Chemistry, University of Science and Technology of China, Hefei, Anhui 230026, China
Received: October 24, 2007
In Final Form: December 21, 2007
Abstract:
This paper reports that extremely strongly coupled excitonic states were formed in H-aggregated monocrystalline nanosheets and semicrystalline nanowires of coplanar organic molecules of 2,5-bis(4-methoxybenzylidene) cyclopentanone, due to the highly regular face-to-face stacking of molecular excitons. It was demonstrated that the spectral absorption and fluorescence emission behaviors are dependent on the routes of molecular aggregation and the ordered degree of molecular arrangement in aggregated nanoparticles. In particular, the H-type aggregation of molecules through a highly ordered molecular arrangement in the monocrystalline nanosheets led to the formation of a new exciton coupling state with an energy band higher than that in normal semi-/noncrystalline H-aggregation. A strong symmetric absorption at higher energy bands was thus observed in the solution of nanosheets. Furthermore, the strongly coupled excitonic state may hold all the oscillator strength, leading to the extinction of the original intramolecular electronic transitions of individual molecules and the appearance of new strong absorption and fluorescence emissions at high-energy bands. These results show a perspective that the ability to control the molecular structure and its arrangement in aggregates holds promise for creating novel optical properties in molecular materials.
Download the full text: PDF | HTML
