Ethynyl-tetracene dimers, where linkage is made via a phenyl bridge, have been synthesized with the chromophore units at ortho-, meta- and para- configurations as well as a similarly bridged ethynyl-linked tetramer. Ultrafast electronic spectroscopy of such multimers in solution allow the investigation of the contributions of through-space and through-bond coupling to the rate of singlet fission as well as the role of entropy. Transient absorption spectroscopy has been used to observe the singlet state, the correlated triplet state and the separated triplet states in these multimers. The spectral deconvolution of the transient absorption data shows that the only the para-dimer forms separated triplets while the ortho-dimer only forms the correlated triplet pair while the meta-dimer does not undergo singlet fission at all. Rate enhancement in a tetramer is understood through consideration of the increased entropic driving force. The role of the charge transfer state in symmetric dimers will also be considered via comparisons to systems that achieve rapid and log-lived charge separation to a radical pair, which then proceeds via slow conversion to a single overall triplet.

Fission and charge transfer with minimal energy loss

ACS Spring Meeting 2021

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