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Charge-transfer biexciton annihilation in a donor-acceptor co-crystal yields high-energy long-lived charge carriers
Organic donor-acceptor (D-A) co-crystals have attracted much interest due to their important optical and electronic properties. Co-crystals having DADA π-stacked morphologies are especially interesting because photoexcitation produces a charge-transfer (CT) exciton, D&z.rad; + -A&z.rad; − ,...
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Published in: | Chemical science (Cambridge) 2020-09, Vol.11 (35), p.9532-9541 |
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Main Authors: | , , , , , , , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | Organic donor-acceptor (D-A) co-crystals have attracted much interest due to their important optical and electronic properties. Co-crystals having DADA π-stacked morphologies are especially interesting because photoexcitation produces a charge-transfer (CT) exciton, D&z.rad;
+
-A&z.rad;
−
, between adjacent D-A molecules. Although several studies have reported on the steady-state optical properties of this type of CT exciton, very few have measured the dynamics of its formation and decay in a single D-A co-crystal. We have co-crystallized a
peri
-xanthenoxanthene (
PXX
) donor with a
N
,
N
-bis(3-pentyl)-2,5,8,11-tetraphenylperylene-3,4:9,10-bis(dicarboximide) (
Ph
4
PDI
) acceptor to give an orthorhombic
PXX
-
Ph
4
PDI
DADA π-stacked co-crystal with a CT transition dipole moment that is perpendicular to the transition moments for S
n
← S
0
excitation of
PXX
and
Ph
4
PDI
. Using polarized, broadband, femtosecond pump-probe microscopy, we have determined that selective photoexcitation of
Ph
4
PDI
in the single co-crystal results in CT exciton formation within the 300 fs instrument response time. At early times (0.3 ≤
t
≤ 500 ps), the CT excitons decay with a
t
−1/2
dependence, which is attributed to CT biexciton annihilation within the one-dimensional DADA π-stacks producing high-energy, long-lived (>8 ns) electron-hole pairs in the crystal. These energetic charge carriers may prove useful in applications ranging from photovoltaics and opto-electronics to photocatalysis.
Femtosecond transient absorption microscopy of donor-acceptor single co-crystals shows that photogenerated charge transfer excitons in one-dimensional donor-acceptor π stacks annihilate to produce high-energy, long-lived electrons and holes. |
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ISSN: | 2041-6520 2041-6539 |
DOI: | 10.1039/d0sc03301d |