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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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Bibliographic Details
Published in:Chemical science (Cambridge) 2020-09, Vol.11 (35), p.9532-9541
Main Authors: Schlesinger, Itai, Powers-Riggs, Natalia E, Logsdon, Jenna L, Qi, Yue, Miller, Stephen A, Tempelaar, Roel, Young, Ryan M, Wasielewski, Michael R
Format: Article
Language:English
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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.
ISSN:2041-6520
2041-6539
DOI:10.1039/d0sc03301d