Journal
ACS NANO
Volume 6, Issue 6, Pages 5507-5513Publisher
AMER CHEMICAL SOC
DOI: 10.1021/nn301410j
Keywords
oligothiophene; morphology; aggregate; spectroscopy; Kelvin probe force microscopy
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Funding
- Understanding Charge Separation and Transfer at Interfaces in Energy Materials (EFRC:CST), an Energy Frontier Research Center
- U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-SC0001091]
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Solution processing of oligothiophene molecules is shown to produce a range of particles with distinct morphologies. Once isolated on a substrate, the optical and electronic properties of individual particles were studied. From polarized scanning confocal microscopy experiments, distinct particles that are identifiable by shape were shown to have similar emission spectra except in regard to the 0-0 vibronic band intensity. This suppression of the 0-0 vibronic band correlates to the amount of energetic disorder present in a weakly coupled H-aggregate. The studied particles ranged from moderate to almost complete suppression of the 0-0 vibronic band when compared to the emission spectrum of the isolated molecule in solution. All particles were found to have a high degree of geometric order (molecular alignment) as observed from the fluorescence dichroism (FD) values of around 0.7-0.8 for all the studied morphologies. The structural and electronic properties of the particles were investigated with Kelvin probe force microscopy (KPFM) to measure the local contact potential (LCP) difference, a quantity that is closely related to the differences in intermolecular charge distribution between the oligothiophene particles. The LCP was found to vary by as much as 70 mV between different oligothiophene particles and a trend was observed that correlated the LCP changes with the amount of energetic disorder present, as signified by the suppression of the 0-0 vibronic peak in the emission spectra. Combined polarized scanning confocal microscopy studies, along with KPFM measurements, help to provide fundamental insights into the role of morphology, molecular packing, and intermolecular charge distributions in oligiothiophene particles.
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