Cyanine Dye H- and J-Aggregates
Coherent coupling of molecular dipoles in dye molecules leads to a delocalized photo-excited state. Optoelectronic properties of these dye aggregates are a narrow excitonic absorption band, super radiant emission, efficient energy migration and super-quenching.
We investigate this molecular coupling and the resulting exciton and charge transport properties.
While the H-aggregate dimer is known to be non-luminescent, a long-lived, and quenchable fluorescence with high quantum yield can be attributed to dimers in a twisted configuration.
Figure: An anomalous photoluminescence with high quantum yield is assigned to “twisted” dimers in the solid state. Reprinted from J. Phys. Chem. C 2017, Copyright 2017 American Chemical Society. This is an open access published under an ACS AuthorChoice License.
S. B. Anantharaman et al., Strongly Red-Shifted Photoluminescence Band Induced by Molecular Twisting in Cyanine (Cy3) Dye Films, The Journal of Physical Chemistry C, 2017, DOI: 10.1021/acs.jpcc.7b01412 (open access). http://pubs.acs.org/doi/suppl/10.1021/acs.jpcc.7b01412
Besides in silver halide photography, industrial applications of dye aggregates are hampered due to difficulties in producing aggregates reproducibly, with controlled size and perfection and avoiding complex manufacturing processes such as Langmuir-Blodgett techniques.
While cyanine dye aggregates are best known for intense and narrow absorption bands, our films stick out for prominent scattering in the absorption band (resonance light scattering). Similar to localized surface plasmon resonances (LSPR), scattering can be explained with the coherently oscillating electron cloud of the aggregate in response to incident light. Because dye aggregate extinction has narrowest bandwidths, the wavelength selectivity exceeds the selectivity of localized surface plasmon resonances. Dye aggregation enhances scattering effects in structured dye film (see Optical Properties of Organic Thin Films).
J.-N. Tisserant et al. Resonance Light Scattering in Dye-Aggregates Forming in Dewetting Droplets,
ACS Nano, 2014 (8) 10057-10065
SNF: Fundamental studies of mesoscopic devices for solar energy conversion
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