Small Reorganization Energies of Photoinduced Electron Transfer between Spherical Fullerenes

Abstract

Rate constants of photoinduced electron transfer between spherical fullerenes were determined using triscandium nitride encapsulated C80 fullerene (Sc3N@C80) as an electron donor and the triplet excited state of lithium ion-encapsulated C60 fullerene (Li(+)@C60) as an electron acceptor in polar and less polar solvents by laser flash photolysis measurements. Upon nanosecond laser excitation at 355 nm of a benzonitrile (PhCN) solution of Li(+)@C60 and Sc3N@C80, electron transfer from Sc3N@C80 to the triplet excited state [(3)(Li(+)@C60)*] occurred to produce Sc3N@C80(•+) and Li(+)@C60(•-) (λ(max) = 1035 nm). The rates of the photoinduced electron transfer were monitored by the decay of absorption at λ(max) = 750 nm due to (3)(Li(+)@C60)*. The second-order rate constant of electron transfer from Sc3N@C80 to (3)(Li(+)@C60)* was determined to be k(et) = 1.5 × 10(9) M(-1) s(-1) from dependence of decay rate constant of (3)(Li(+)@C60)* on the Sc3N@C80 concentration. The rate constant of back electron transfer from Li(+)@C60(•-) to Sc3N@C80(•+) was also determined to be k(bet) = 1.9 × 10(9) M(-1) s(-1), which is close to be the diffusion limited value in PhCN. Similarly, the rate constants of photoinduced electron transfer from C60 to (3)(Li(+)@C60)* and from Sc3N@C80 to (3)C60* were determined together with the back electron-transfer reactions. The driving force dependence of log k(et) and log k(bet) was well fitted by using the Marcus theory of outer-sphere electron transfer, in which the internal (bond) reorganization energy (λi) was estimated by DFT calculations and the solvent reorganization energy (λs) was calculated by the Marcus equation. When PhCN was replaced by o-dichlorobenzene (o-DCB), the λ value was decreased because of the smaller solvation changes of highly spherical fullerenes upon electron transfer in a less polar solvent.

Hydratisierung von und auf Oberflächen

“…in which Δ e is the amount of transferred charge (Δ e = e ); ε 0 is the dielectric constant in a vacuum; r A and r D are the van der Waals radii of electron donor and acceptor, respectively; d is the contact distance between fullerenes; ε op is optical dielectric constant ( ε op = n 2 , in which n is refractive index; and ε s is the dielectric constant of the solvent 62. The predicted λ value is 0.67 eV in PhCN, which agrees with observed driving force dependence of k et 65. Fullerenes, which have a highly delocalized 3D π‐conjugated system, generally have small reorganization energies 65.…”

“…The predicted λ value is 0.67 eV in PhCN, which agrees with observed driving force dependence of k et 65. Fullerenes, which have a highly delocalized 3D π‐conjugated system, generally have small reorganization energies 65. The small reorganization energy and strong electron‐acceptor ability of Li + @C 60 are suitable for efficient electron transfer with electron donors.…”

Efficient Charge Separation in Li+@C60 Supramolecular Complexes with Electron Donors

“…[65] Fullerenes, which have a highly delocalized 3D p-conjugated system, generally have small reorganization energies. [65] The small reorganization energy and strong electron-acceptor ability of Li + @C 60 are suitable for efficient electron transfer with electron donors.…”

“…[65] Fullerenes, which have a highly delocalized 3D p-conjugated system, generally have small reorganization energies. [65] The small reorganization energy and strong electron-acceptor ability of Li + @C 60 are suitable for efficient electron transfer with electron donors. 1035 [52] one-electron reduction potential (vs. SCE) [V] À0.43 [53] + 0.14 [52] absorption of singlet excited state [nm] 920 [58] 960 [59] absorption of triplet excited state [nm] 740 [58] 750 [59] lifetime of singlet excited state [ns] 2.4 [58] 1.1 [59] lifetime of triplet excited state [ms] 48 [60] 49 [59] singlet excited energy [eV] 1.99 [58] 1.94 [59] triplet excited energy [eV] 1.57 [58] 1.53 [59] There have been many reports on using electron donor-acceptor linked molecules to achieve long-lived photoinduced charge-separated (CS) states.…”

Van der Waals effects on structure and optical properties in organic photovoltaics

“…Organic bulk heterojunction (BHJ) solar cells that consist of blends of an electron donor, usually a π ‐conjugate polymer like poly(3‐hexylthiophene) (P3HT), and an electron acceptor, usually a fullerene derivative like [6,6]‐phenyl‐C 61 ‐butyric acid methyl ester (PCBM), are among the most efficient OPV cells reported to date, reaching power conversion efficiencies (PCEs) of η > 10% . The fact that fullerene C 60 and derivatives are taken into consideration in the design of OPV cells is mainly due to their excellent electron acceptor capability, and also because of their small inner‐sphere reorganization energy …”