Pentacene-bridge interactions in singlet fission pentacene dimers
Associate Professor Girish Lakhwani
- University of Sydney
Wednesday 23 November, 10am
Abstract
Singlet fission (SF), the conversion of one singlet exciton into two triplets, offers a promising pathway to overcome thermalization losses and surpass the detailed balance limit in single junction solar cells. [1] Insights into the SF process developed in the last few years have been led by investigation into the excited state dynamics of designer molecular systems where SF-based chromophores are covalently linked by a bridging molecule. However, little is known about chromophore-bridge interactions that is crucial towards the rational design of efficient SF-based chromophores.
Here, I’ll discuss our recent work on a novel singlet fission pentacene dimer (BNBP) containing an axially chiral binaphthyl bridging unit. With the help of time-resolved TA and ESR, we unambiguously show that SF dynamics in BNBP involves the formation of a very long-lived intermediate triplet pair (TT) state. Interestingly, the triplet-triplet recombination in the TT state is significantly suppressed. Analysis of CD and excited state CD responses together with TD-DFT calculations reveal a significant contribution from the binaphthyl bridge to the high-energy singlet transitions in BNBP. We propose that the wavefunction overlap between the pentacene units and the binaphthyl bridge aids in the significant suppression of the triplet-triplet recombination in BNBP and emphasise the role of the frontier molecular orbitals of the bridge on the decay dynamics of the TT state. [2]
More generally, we analyse magnetic circular dichroism (MCD) spectra of various covalently bridged pentacene dimers to study the role of the molecular structure of the bridge on the extent of ‘through-space’ coulombic and ‘through-bond’ exchange interactions between pentacene chromophores. Our results show that ‘through-bond’ interactions are significant in dimers incorporating conjugated molecules as bridging units. [3]
Our work underlines the innovative use of chiroptical techniques to sensitively investigate pentacene-bridge interactions and their impact on multiexciton dynamics.
References
- W. Shockley and H.J. Queisser, “Detailed Balance Limit of Efficiency of pn Junction Solar Cells” J. Appl. Phys. 32, 510 (1961)
- A. Sharma et al, “Pentacene-bridge interactions in axially chiral binaphthyl pentacene dimer” J. Phys. Chem. A, 125, 7226, (2021).
- A. Sharma et al, “Probing Through-Bond and Through-Space Interactions in Singlet Fission-Based Pentacene Dimers” J. Phys. Chem. Lett., 13, 8978, (2022).
About the speaker
Girish Lakhwani's expertise covers chiroptical spectroscopy, single molecule spectroscopy, device physics and master equation based coarse-grained simulations.
He coordinates programs across the Centre's themes of materials, theory, instrumentation and devices.
