2 research outputs found
Temporal fluctuations in excimer-like interactions between pi-conjugated chromophores
Inter- or intramolecular coupling processes between chromophores such as
excimer formation or H- and J-aggregation are crucial to describing the
photophysics of closely packed films of conjugated polymers. Such coupling is
highly distance dependent, and should be sensitive to both fluctuations in the
spacing between chromophores as well as the actual position on the chromophore
where the exciton localizes. Single-molecule spectroscopy reveals these
intrinsic fluctuations in well-defined bi-chromophoric model systems of
cofacial oligomers. Signatures of interchromophoric interactions in the excited
state - spectral red-shifting and broadening, and a slowing of
photoluminescence decay - correlate with each other but scatter strongly
between single molecules, implying an extraordinary distribution in coupling
strengths. Furthermore, these excimer-like spectral fingerprints vary with
time, revealing intrinsic dynamics in the coupling strength within one single
dimer molecule, which constitutes the starting point for describing a molecular
solid. Such spectral sensitivity to sub-Angstrom molecular dynamics could prove
complementary to conventional FRET-based molecular rulers
Temporal Switching of Homo-FRET Pathways in Single-Chromophore Dimer Models of π‑Conjugated Polymers
A set of π-conjugated oligomer dimers templated
in molecular
scaffolds is presented as a model system for studying the interactions
between chromophores in conjugated polymers (CPs). Single-molecule
spectroscopy was used to reveal energy transfer dynamics between two
oligomers in either a parallel or oblique-angle geometry. In particular,
the conformation of single molecules embedded in a host matrix was
investigated via polarized excitation and emission fluorescence microscopy
in combination with fluorescence correlation spectroscopy. While the
intramolecular interchromophore conformation was found to have no
impact on the fluorescence quantum yield, lifetime, or photon statistics
(antibunching), the long-term nonequilibrium dynamics of energy transfer
within these bichromophoric systems was accessible by studying the
linear dichroism in emission at the single-molecule level, which revealed
reversible switching of the emission between the two oligomers. In
bulk polymer films, interchromophore coupling promotes the migration
of excitation energy to quenching sites. Realizing the presence and
dynamics of such interactions is crucial for understanding limitations
on the quantum efficiency of larger CP materials