Ultrafast Two-Electron Transfer in a CdS Quantum Dot–Extended-Viologen Cyclophane Complex

Abstract

Time-resolved optical spectroscopies reveal multielectron transfer from the biexcitonic state of a CdS quantum dot to an adsorbed tetracationic compound cyclobis(4,4'-(1,4-phenylene) bipyridin-1-ium-1,4-phenylene-bis(methylene)) (ExBox(4+)) to form both the ExBox(3+•) and the doubly reduced ExBox(2(+•)) states from a single laser pulse. Electron transfer in the single-exciton regime occurs in 1 ps. At higher excitation powers the second electron transfer takes ∼5 ps, which leads to a mixture of redox states of the acceptor ligand. The doubly reduced ExBox(2(+•)) state has a lifetime of ∼10 ns, while CdS(+•):ExBox(3+•) recombines with multiple time constants, the longest of which is ∼300 μs. The long-lived charge separation and ability to accumulate multiple charges on ExBox(4+) demonstrate the potential of the CdS:ExBox(4+) complex to serve as a platform for two-electron photocatalysis.

An artificial photosynthetic system for photoaccumulation of two electrons on a fused dipyridophenazine (dppz)–pyridoquinolinone ligand

“…Since the initial report by Wasielewski and co-workers in 1992, 14 a few molecular systems have been reported that photoaccumulate reducing equivalents. 15 – 17 The electron storage sites range from organic structures such as naphthalene or perylene bisimides, 14 , 18 anthraquinone, 19 and viologen derivatives, 20 , 21 to iridium( iii ) 22 or rhodium( iii ) 23 complexes and polyoxometalates. 24 , 25 Ruthenium complexes containing NAD(P) + /NAD(P)H mimics were also elegantly developed by the group of Tanaka.…”

Hot electron transfer in Zn–Ag–In–Te nanocrystal–methyl viologen complexes enhanced with higher-energy photon excitation

“…Charge separation dynamics with the use of various electron acceptors has been reported in many papers. [5][6][7][8][9][10][11][12][13][14][15][16][17] For example Banin et al reported that hybrid nanostructures of Au-tipped CdS nanorods with a larger Au size exhibited a higher probability for charge separation of multiple excitons formed in the CdS nanocrystals, improving the photocatalytic activity for H 2 generation. 15 The rate of photoinduced electron transfer from CdSe NCs to methyl viologen (MV 2+ ) was shown to be dependent on the particle morphology: plate-like CdSe NCs exhibited a slower rate than that of spherical or rod-shaped CdSe NCs due to the weak electronic coupling along the short and long axes in the lateral dimension.…”

Competition between Singlet Fission and Spin‐Orbit‐Induced Intersystem Crossing in Anthanthrene and Anthanthrone Derivatives

“…Solution samples were prepared in 2 mm path length glass cuvettes and degassed with three freeze‐pump‐thaw cycles. The TA data were subjected to global kinetic analysis to obtain the evolution‐ and decay‐associated spectra and kinetic parameters as described in detail previously …”

“…The TA data were subjected to global kinetic analysis to obtain the evolution-and decayassociated spectra and kinetic parameters as described in detail previously. [20]…”