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Excitation Energy Transfer within Covalent Tetrahedral Perylenediimide Tetramers and Their Intermolecular Aggregates

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Citation

Ramanan, C., Kim, C. H., Marks, T. J., & Wasielewski, M. R. (2014). Excitation Energy Transfer within Covalent Tetrahedral Perylenediimide Tetramers and Their Intermolecular Aggregates. The Journal of Physical Chemistry C, 118(30), 16941-16950. doi:10.1021/jp500475c.


Cite as: http://hdl.handle.net/21.11116/0000-0005-4A43-D
Abstract
Perylenediimides (PDIs) offer a number of attractive characteristics as alternatives to fullerenes in organic photovoltaics (OPVs), including favorable orbital energetics, high extinction coefficients in the visible spectral region, photostability, and the capacity to self-assemble into ordered nanostructures. However, energy transfer followed by charge separation in PDI assemblies must kinetically out-compete excimer formation that limits OPV performance. We report on the excitation energy transfer (EET) rate in a covalently linked PDI tetramer in which the PDI chromophores are arranged in a tetrahedral geometry about a tetraphenyladamantane core. Transient absorption spectroscopy of the tetramer in CH2Cl2 reveals a laser intensity-dependent fast absorption decay component indicative of singlet?singlet annihilation resulting from intramolecular EET. Femtosecond fluorescence anisotropy measurements show that the EET time constant τ = 6 ps, which is similar to that predicted for a through-space F\"{o}}rster EET mechanism. Concentration-dependent steady-state spectroscopic studies reveal the formation of intermolecular aggregates of the tetramers in toluene. The aggregates are formed by cofacial π-stacking interactions between PDIs of neighboring tetramers. Transient absorption spectra of the aggregated tetramers in toluene solution demonstrate long-lived excited-state decay dynamics (τ ? 30 ns) in agreement with previous observations of PDI excimers. Perylenediimides (PDIs) offer a number of attractive characteristics as alternatives to fullerenes in organic photovoltaics (OPVs), including favorable orbital energetics, high extinction coefficients in the visible spectral region, photostability, and the capacity to self-assemble into ordered nanostructures. However, energy transfer followed by charge separation in PDI assemblies must kinetically out-compete excimer formation that limits OPV performance. We report on the excitation energy transfer (EET) rate in a covalently linked PDI tetramer in which the PDI chromophores are arranged in a tetrahedral geometry about a tetraphenyladamantane core. Transient absorption spectroscopy of the tetramer in CH2Cl2 reveals a laser intensity-dependent fast absorption decay component indicative of singlet?singlet annihilation resulting from intramolecular EET. Femtosecond fluorescence anisotropy measurements show that the EET time constant τ = 6 ps, which is similar to that predicted for a through-space F{\"{o}rster EET mechanism. Concentration-dependent steady-state spectroscopic studies reveal the formation of intermolecular aggregates of the tetramers in toluene. The aggregates are formed by cofacial π-stacking interactions between PDIs of neighboring tetramers. Transient absorption spectra of the aggregated tetramers in toluene solution demonstrate long-lived excited-state decay dynamics (τ ? 30 ns) in agreement with previous observations of PDI excimers.