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Synthesis and Exciton Dynamics of Donor-Orthogonal Acceptor Conjugated Polymers: Reducing the Singlet-Triplet Energy Gap.

David M E FreemanAndrew J MusserJarvist M FrostHannah L SternAlexander K ForsterKealan J FallonAlexandros G RapidisFranco CacialliIain McCullochTracey M ClarkeRichard H FriendHugo Bronstein
Published in: Journal of the American Chemical Society (2017)
The presence of energetically low-lying triplet states is a hallmark of organic semiconductors. Even though they present a wealth of interesting photophysical properties, these optically dark states significantly limit optoelectronic device performance. Recent advances in emissive charge-transfer molecules have pioneered routes to reduce the energy gap between triplets and "bright" singlets, allowing thermal population exchange between them and eliminating a significant loss channel in devices. In conjugated polymers, this gap has proved resistant to modification. Here, we introduce a general approach to reduce the singlet-triplet energy gap in fully conjugated polymers, using a donor-orthogonal acceptor motif to spatially separate electron and hole wave functions. This new generation of conjugated polymers allows for a greatly reduced exchange energy, enhancing triplet formation and enabling thermally activated delayed fluorescence. We find that the mechanisms of both processes are driven by excited-state mixing between π-π*and charge-transfer states, affording new insight into reverse intersystem crossing.
Keyphrases
  • energy transfer
  • photodynamic therapy
  • quantum dots
  • solar cells