Damrauer, Niels H. Hodgkiss, Justin M. Rosenthal, Joel Nocera, Daniel G. Observation of Proton-Coupled Electron Transfer by Transient Absorption Spectroscopy in a Hydrogen-Bonded, Porphyrin Donor−Acceptor Assembly Proton-coupled electron transfer (PCET) kinetics of a Zn(II) porphyrin donor noncovalently bound to a naphthalene-diimide acceptor through an amidinium-carboxylate interface have been investigated by time-resolved spectroscopy. The S<sub>1</sub> singlet excited-state of a Zn(II) 2-amidinium-5,10,15,20-tetramesitylporphyrin chloride (ZnP-β-AmH<sup>+</sup>) donor is sufficiently energetic (2.04 eV) to reduce a carboxylate-diimide acceptor (Δ<i>G</i>° = −460 mV, THF). Static quenching of the porphyrin fluorescence is observed and time-resolved measurements reveal more than a 3-fold reduction in the S<sub>1</sub> lifetime of the porphyrin upon amidinium-carboxylate formation (THF, 298 K). Picosecond transient absorption spectra of the free ZnP-β-AmH<sup>+</sup> in THF reveal the existence of an excited-state isosbestic point between the S<sub>1</sub> and T<sub>1</sub> states at λ<sub>probe</sub> = 650 nm, providing an effective ‘zero-kinetics' background on which to observe the formation of PCET photoproducts. Distinct rise and decay kinetics are attributed to the build-up and subsequent loss of intermediates resulting from a forward and reverse PCET reaction, respectively (<i>k</i><sub>PCET</sub>(fwd) = 9 × 10<sup>8</sup> s<sup>-1</sup> and <i>k</i><sub>PCET</sub>(rev) = 14 × 10<sup>8</sup> s<sup>-1</sup>). The forward rate constant is nearly 2 orders of magnitude slower than that measured for covalently linked Zn(II) porphyrin−acceptor dyads of comparable driving force and D−A distance, establishing the importance of a proximal proton network in controlling charge transport. T 1 states;kinetic;Transient Absorption Spectroscopy;THF;formation;acceptor;Zn;ZnP;porphyrin;S 1 lifetime;k PCET;donor 2004-05-20
    https://acs.figshare.com/articles/journal_contribution/Observation_of_Proton_Coupled_Electron_Transfer_by_Transient_Absorption_Spectroscopy_in_a_Hydrogen_Bonded_Porphyrin_Donor_Acceptor_Assembly/3338737
10.1021/jp049296b.s001