Balancing Panchromatic Absorption and Multistep Charge Separation in a Compact Molecular Architecture
- Washington Univ., St. Louis, MO (United States)
- North Carolina State Univ., Raleigh, NC (United States)
- Univ. of California, Riverside, CA (United States)
A panchromatic triad and a charge-separation triad are joined in a crossbar architecture to capture solar energy. The panchromatic triad (T) is comprised of a central free-base porphyrin that is strongly coupled via direct ethyne linkages to two perylene-monoimides. Here, the charge-separation unit incorporates a free-base or zinc chlorin (C or ZnC) as a hole acceptor (or electron donor) and a perylene-diimide (PDI) as an electron acceptor, both attached to the porphyrin via diphenylethyne linkers. The free-base porphyrin is common to both light-harvesting and charge-separation motifs. The chlorin and PDI also function as ancillary light absorbers, complementing direct excitation of the panchromatic triad to produce the discrete lowest excited state of the array (T*). Attainment of full charge separation across the pentad entails two steps: (1) an initial excited-state hole/electron transfer process to oxidize the chlorin (and reduce the triad) or reduce the PDI (and oxidize the triad); and (2) subsequent ground-state electron/hole migration to produce oxidized chlorin and reduced PDI. Full charge separation for pentad ZnC-T-PDI to generate ZnC+-T-PDI¯ occurs with a quantum yield of ~30% and mean lifetime ~1 μs in dimethyl sulfoxide. For C-T-PDI, initial charge separation is followed by rapid charge recombination. The molecular designs and studies reported here reveal the challenges of balancing the demands for charge separation (linker length and composition, excited-state energies, redox potentials, and medium polarity) with the constraints for panchromatic absorption (strong electronic coupling of the porphyrin and two perylene-monoimide units) for integrated function in solar-energy conversion.
- Research Organization:
- Washington Univ., St. Louis, MO (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences & Biosciences Division
- Grant/Contract Number:
- FG02-05ER15661
- OSTI ID:
- 1905441
- Journal Information:
- Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory, Vol. 126, Issue 50; ISSN 1089-5639
- Publisher:
- American Chemical SocietyCopyright Statement
- Country of Publication:
- United States
- Language:
- English
Similar Records
Investigation of a bacteriochlorin-containing pentad array for panchromatic light-harvesting and charge separation
Electronic Structure and Excited-State Dynamics of Rylene–Tetrapyrrole Panchromatic Absorbers