Ethyne-bridged porphyrin arrays remain promising as electron-accepting motifs which possess strong and broad spectral coverage, qualities which are crucial for the development of photovoltaic materials. By substituting the highly conjugated zinc porphyrin core with non-π conjugating, highly σ-withdrawing perfluoroalkyl groups, frontier molecular orbitals are dramatically stabilized while conserving band gap. Alternating electron-rich (donor) and electron-poor (acceptor) porphyrin arrays have been shown to possess high-oscillator strength lowest-energy transitions facilitated by strong excitonic coupling between monomeric porphyrin units. In order to characterize and harness the stabilizing electron-withdrawing nature of perfluoroalkyl substituents in these systems, a series of monomeric perfluoroalkyl porphyrins has been developed. Herein I discuss strategies for engineering strongly absorbing electron-deficient materials by investigating the photophysics of zinc porphyrins modified with perfluoroalkyl substituents using a combination of steady state, ultrafast, electrochemical and electron paramagnetic resonance spectroscopies. Specifically, we revealed that conjugation elaboration via acetylene substitution stabilizes ground state oxidation (E0/+) and drastically red-shifts fluorescence while substitution of perfluoroalkyl groups stabilizes ground state reduction (E-/0) potentials and frontier molecular orbitals. Corresponding butadiyne-bridged perfluoroalkyl dimer and trimer arrays reveal even more dramatic stabilization, establishing these arrays as a promising new scaffolding for n-type semiconducting materials. The ability to manipulate excited state processes in this series motivates incorporation of perfluoroalkyl-substituted zinc porphyrin arrays as conjugated electron acceptors in photovoltaic devices. Observed trends including narrowed lowest energy singlet (S1) and triplet (T1) excited state band gaps and monomeric-like excited state reduction potentials of perfluoroalkyl arrays indicate that these systems enable fine-tuning of associated photophysics. With the ability to probe and control these excited state processes, we can optimize components crucial for photovoltaics including excitonic delocalization, charge separation and subsequent polaron mobility.

Control of photophysics in conjugated perfluoroalkyl zinc porphyrin electron acceptors

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.