Symmetric dimers have the potential to optimize charge separation and energy transfer in optoelectronic devices. Here, terthiophene chromophores are symmetrically bridged about a sulfur atom and their photophysics are characterized with steady-state and time-resolved spectroscopy. A remarkable enhancement of the photoluminescence quantum yield is observed as the sulfur bridge is oxidized from sulfide (S) to sulfoxide (SO) to sulfone (SO<sub>2</sub>). Transient absorption spectroscopy reveals that, upon photoexcitation, a delocalized charge resonance state forms. Rapid geometrical relaxation within 10 ps breaks the symmetry and leads to a charge transfer state. While high polarity solvents can enhance the charge transfer character of covalent dimers, the oxidation state of the bridging sulfur group provides an additional way to tune the electronic coupling between each chromophore within the dimer. Computational results indicate that the lone pairs on the bridging sulfur group screen the electronic interactions between chromophores. Increasing the oxidation state of the bridge removes the electron density from the bridging sulfur resulting in enhanced interchromophore interactions and enhanced charge transfer character in the intermediate state. The increased photoluminescence of the sulfur-bridged terthiophene dimers is the result of a decreased intersystem crossing rate from the intermediate charge transfer state. Modifying the bridging atom oxidation state provides a unique intramolecular “handle” to tune the electronic interactions between chromophores without altering solvent polarity or dimer geometry. Work is now underway on a class of sulfur-bridged Ru complexes where we plan to explore the effect of the bridge oxidation state on chromophores which do not contain sulfur.

Controlling interchromophore coupling in symmetric dimers: The role of bridge's electronic structure

251st National Meeting (2016)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.