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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 39: Focus Session: Ultrafast Processes in Organic Semiconductors and Perovskites I (joint session O/CPP)
CPP 39.3: Talk
Thursday, March 21, 2024, 11:15–11:30, MA 004
Efficient Intramolecular Singlet Fission in Weakly-Interacting Heterodimers — •Oskar Kefer1, Lukas Ahrens2, Jie Han3, Jan Freudenberg2, Frank Rominger2, Andreas Dreuw3, Uwe H. F. Bunz2, and Tiago Buckup1 — 1PCI, Universität Heidelberg, Heidelberg — 2OCI, Universität Heidelberg, Heidelberg — 3IWR, Universität Heidelberg, Heidelberg
Intramolecular singlet fission (iSF) converts one excited singlet (S1S0) into two triplets when two chromophores are covalently bound by a bridge. The bridge also determines the strength of intramolecular interaction. Usually, strong interaction leads to fast formation of the intermediate correlated triplet-pair (1[T1T1]), but also hinders its dissociation. A Spiro-linker enforces a perpendicular π-system-arrangement around the central spiro-carbon, leading to long triplet-lifetimes that favor separation into T1+T1 without compromising 1[T1T1]-formation efficiency.
We expand on this approach and demonstrate a new class of heterodimers that exploit the favorable properties of spiro-conjugation with enhanced iSF dynamics. Quantum-chemical calculations (DFT) and transient absorption spectroscopy link accelerated iSF-kinetics to changes in the S1S0- and 1[T1T1]-energy landscape. The limited interaction during the lifetime of 1[T1T1] creates favorable conditions for triplet-separation, which are formed with a yield of up to 174%. This new approach furnishes efficient heterogeneous iSF materials with reduced intramolecular interaction due to spatial fixation between chromophores and large, tunable absorption bandwidths.
Keywords: singlet fission; ultrafast; triplet; spiro; pump probe