Self-assembly and Nanostructures  
Liquid-Liquid Dewetting
Cyanine dye H- and J-aggregates
Thin Film Single Crystals

Cyanine Dye H and J-Aggregates

 

Specific to dye aggregates is a large scale coherent coupling of molecular dipoles, leading to a delocalized photo-excited state. Optoelectronic properties are a narrow excitonic absorption band, super radiant emission, efficient energy migration and super-quenching.
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.
We pioneer a new method to manufacture dye aggregates by spontaneous assembly of dye molecules into H-aggregates during film formation.

 

Figure: H-aggregates form spontaneously in nano-porous PCBM domains that form during liquid-liquid dewetting (a). The nanostructure becomes visible when selectively dissolving the caps of the PCBM domains (b). In the as-cast films H-aggregates form (c). Reprinted with permission from Lang-muir 2010, 26, 3955. Copyright 2014 American Chemical Society.

 

References: J. Heier et al., Template Synthesis of Cyanine Dye H-aggregates on Nano-structured [6,6]- Phenyl C61-Butyric Acid Methyl Ester Substrates, Phys. Chem. Chem. Phys., 2011, 13, 15714 – 15722; J. Heier et al., Fast assembly of cyanine dyes onto [6,6]-phenyl C61-butyric acid methyl ester surfaces from organic solvents, Langmuir 2010, 26, 3955.

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. We here investigate Resonance Light Scattering (RLS) of dye aggregates in thin films.

 

Figure: From the large attenuance peak of the H-aggregate, only a small fraction can be assigned to absorption (a). A larger fraction of light is resonantly scattered into a ring representing the Fourier Transformation of the film topography (b). Reprinted with permission from ACS Nano doi: 10.1021/nn5040839. Copyright 2014 American Chemical Society.

Reference: J.-N. Tisserant et al. Resonance Light Scattering in Dye-Aggregates Forming in

Dewetting Droplets, ACS Nano, 2014, doi: 10.1021/nn5040839.

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