Sequential Proton-Coupled Electron Transfer Mediates Excited-State Deactivation of a Eumelanin Building Block

Benzimidazole phenol-porphyrin dyads have been synthesized to study proton-coupled electron transfer (PCET) reactions induced by photoexcitation. High-potential porphyrins have been chosen to model P680, the photoactive chlorophyll cluster of photosynthetic photosystem II (PSII). They have either two or three pentafluorophenyl groups at the meso positions to impart the high redox potential. The benzimidazole phenol (BIP) moiety models the Tyr[Formula: see text]-His190 pair of PSII, which is a redox mediator that shuttles electrons from the water oxidation catalyst to P680[Formula: see text]. The dyads consisting of a porphyrin and an unsubstituted BIP are designed to study one-electron one-proton transfer (E1PT) processes upon excitation of the porphyrin. When the BIP moiety is substituted with proton-accepting groups such as imines, one-electron two-proton transfer (E2PT) processes are expected to take place upon oxidation of the phenol by the excited state of the porphyrin. The bis-pentafluorophenyl porphyrins linked to BIPs provide platforms for introducing a variety of electron-accepting moieties and/or anchoring groups to attach semiconductor nanoparticles to the macrocycle. The triads thus formed will serve to study the PCET process involving the BIPs when the oxidation of the phenol is achieved by the photochemically produced radical cation of the porphyrin.

Download Full-text

Excited-State Quenching of Porphyrins by Hydrogen-Bonded Phenol-Pyridine Pair: Evidence of Proton-Coupled Electron Transfer

The Journal of Physical Chemistry C ◽

10.1021/acs.jpcc.9b05273 ◽

2019 ◽

Vol 123 (38) ◽

pp. 23342-23351

Author(s):

Munisamy Venkatesan ◽

Haraprasad Mandal ◽

Madhu Chakali ◽

Prakriti Ranjan Bangal

Keyword(s):

Electron Transfer ◽

Excited State ◽

Proton Coupled Electron Transfer ◽

Excited State Quenching ◽

Hydrogen Bonded

Download Full-text

Excited-state proton-coupled electron transfer within ion pairs

Chemical Science ◽

10.1039/c9sc04941j ◽

2020 ◽

Vol 11 (13) ◽

pp. 3460-3473 ◽

Cited By ~ 1

Author(s):

Wesley B. Swords ◽

Gerald J. Meyer ◽

Leif Hammarström

Keyword(s):

Electron Transfer ◽

Excited State ◽

Ion Pairs ◽

Proton Coupled Electron Transfer ◽

General Method ◽

Salicylate Ion

Electrostatic ion pairs provide a general method to study excited-state proton-coupled electron transfer. A PTaETb mechanism is identified for the ES-PCET oxidation of salicylate within photoexcited cationic ruthenium–salicylate ion pairs.

Download Full-text

Excited state structural dynamics of 4-cyano-4′-hydroxystilbene: deciphering the signatures of proton-coupled electron transfer using ultrafast Raman loss spectroscopy

Physical Chemistry Chemical Physics ◽

10.1039/c9cp02923k ◽

2019 ◽

Vol 21 (40) ◽

pp. 22409-22419 ◽

Cited By ~ 2

Author(s):

Reshma Mathew ◽

Surajit Kayal ◽

Adithya Lakshmanna Yapamanu

Keyword(s):

Electron Transfer ◽

Excited State ◽

Structural Dynamics ◽

Transfer Process ◽

Electron Transfer Process ◽

Proton Coupled Electron Transfer

The photo-initiated proton-coupled electron transfer process in the 4-cyano-4′-hydroxystilbene–tert-butylamine adduct strongly affects the excited-state structural dynamics of CHSB.

Download Full-text