Different routes towards triplet states in organic semiconductors: direct S₀→T excitation probed by time-resolved EPR spectroscopy

ABSTRACT

Understanding the electronic structure of semiconducting polymers and their respective building blocks is an essential prerequisite to develop efficient materials for organic electronics. Due to its molecular resolution and capability to directly probe and assign triplet states, (time-resolved) electron paramagnetic resonance spectroscopy is particularly suited. We present here evidence for a direct ${\mathrm{S}}_0\to \mathrm{T}$ optical excitation of distinct triplet states in the small molecule TBT, often used as building block for semiconducting polymers. These states are subtly different in their electronic structure from those populated via intersystem crossing from excited singlet states. With these results, we extend our previous investigations of CbzTBT, the repeat unit of the polymer PCDTBT comprising the TBT and an additional carbazole moiety. Hence, the strong acceptor unit TBT seems responsible for this additional triplet route. Due to the widespread use of TBT as an acceptor unit in many different co-polymers, this has potentially high impact on the efficiency of organic electronic devices.

GRAPHICAL ABSTRACT

KEYWORDS:

• Organic semiconductors
• electronic structure
• triplet pathways
• TBT

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Michael Sommer  http://orcid.org/0000-0002-2377-5998

Till Biskup  http://orcid.org/0000-0003-2913-0004

Additional information

Funding

The authors thank the German Research Foundation (Deutsche Forschungsgemeinschaft, Grant BI-1249/3-1 to T.B., SPP1355 to M.S., IRTG Soft Matter Science 1645, Project SO-1213/8-1 to M.S.) and Albert-Ludwigs-Universität Freiburg (Innovationsfonds Forschung, to T.B., and M.S.) for financial support.