Biphasic Self-Assembly Pathways and Size-Dependent Photophysical Properties of Perylene Bisimide Dye Aggregates

• Published in: Journal of the American Chemical Society Vol. 135; no. 50; pp. 18722 - 18725
• Main Authors: Fennel, Franziska, Wolter, Steffen, Xie, Zengqi, Plötz, Per-Arno, Kühn, Oliver, Würthner, Frank, Lochbrunner, Stefan
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 18-12-2013
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja409597x

The concentration-dependent absorption and temperature-dependent fluorescence of the perylene bisimide dye PBI 1 in methyl­cyclohexane point to a biphasic aggregation behavior. At intermediate concentrations and temperatures, respectively, a dimer with low fluorescence yield dominates, which cannot be extended to longer aggregates. Those are formed at high concentrations and low temperatures, respectively, via a second, energetically unfavorable dimer species that acts as a nucleus. A corresponding aggregation model reproduces accurately the concentration dependence and allows extracting the equilibrium constants and spectra of the distinct species. The differences in the photo­physical properties indicate H-type excitonic coupling for the favored dimer and J-type characteristics for the extended aggregates which could be related to structural models based on DFT calculations. The energetics can be understood by considering hydrogen-bonding and π–π-stacking interactions.