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Photophysical and Electrochemical Characterization of BODIPY-Containing Dyads Comparing the Influence of an A–D–A versus D–A Motif on Excited-State Photophysics
journal contribution
posted on 2016-11-01, 19:04 authored by Samuel
J. Hendel, Ambata M. Poe, Piyachai Khomein, Youngju Bae, S. Thayumanavan, Elizabeth R. YoungA complete photophysical characterization
of organic molecules
designed for use as molecular materials is critical in the design
and construction of devices such as organic photovoltaics (OPV). The
nature of a molecule’s excited state will be altered in molecules
employing the same chromophoric units but possessing different molecular
architectures. For this reason, we examine the photophysical reactions
of two BODIPY-based D–A and A–D–A molecules,
where D is the donor and A is the acceptor. A BODIPY (4,4′-difluoro-4-bora-3a,4a-diaza-s-indacene) moiety serves as the A component and is connected
through the meso position using a 3-hexylthiophene
linker to a N-(2-ethylhexyl)dithieno[3,2-b:2′,3′-d]pyrrole (DTP),
which serves as the D component. An A–D–A motif is compared
to its corresponding D–A dyad counterpart. We show a potential
advantage to the A–D–A motif over the D–A motif
in creating longer-lived excited states. Transient absorption (TA)
spectroscopy is used to characterize the photophysical evolution of
each molecule’s excited state. Global analysis of TA data using
singular value decomposition and target analysis is performed to identify
decay-associated difference spectra (DADS). The DADS reveal the spectral
features associated with charge-transfer excited states that evolve
with different dynamics. A–D–A possess slightly longer
excited-state lifetimes, 42 ps nonradiative decay, and 4.64 ns radiative
decay compared to those of D–A, 24 ps nonradiative decay, and
3.95 ns radiative decay. A longer lived A–D–A component
is observed with microsecond lifetimes, representing a small fraction
of the total photophyscial product. Steady-state and time-resolved
photoluminescence augment the insights from TA, while electrochemistry
and spectroelectrochemistry are employed to identify the nature of
the excited state. Density functional theory supports the observed
electronic and electrochemical properties of the D–A and A–D–A
molecules. These results form a complete picture of the electronic
and photophysical properties of D–A and A–D–A
and provide contextualization for structure–function relationships
between molecules and OPV devices.
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Keywords
photophyscial productphotophysical reactionsdecay-associated difference spectraphotophysical evolutionElectrochemical Characterizationelectrochemical propertiesexcited-state lifetimesExcited-State Photophysicstime-resolved photoluminescenceresults formTA dataphotophysical characterizationmicrosecond lifetimestarget analysisphotophysical propertiesOPV devicesGlobal analysisBODIPY-Containing Dyadsmeso positionmotif3.95 ns radiative decayDTP4.64 ns radiative decayTransient absorptionmoleculechromophoric units3- hexylthiophene linkerD componentvalue decomposition42 ps nonradiative decayDADS
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