Photoinduced Electron Transfer in a Charge-Transfer Complex Formed between Corannulene and Li⁺@C₆₀ by Concave–Convex π–π Interactions

Abstract

A charge-transfer (CT) complex was formed between corannulene (C20H10) and lithium ion-encapsulated [60]fullerene (Li(+)@C60) with the binding constant KG = 1.9 × 10 M(-1) by concave-convex π-π CT interactions in benzonitrile at 298 K, exhibiting a broad CT absorption extended to the NIR region. Femotosecond laser excitation of the C20H10/Li(+)@C60 CT complex resulted in the singlet charge-separated (CS) state, (1)(C20H10(•+)/Li(+)@C60(•-)), which decayed with the lifetime of 1.4 ns. Nanosecond laser excitation of Li(+)@C60 resulted in intermolecular electron transfer (ET) from C20H10 to the triplet excited state of Li(+)@C60 [(3)(Li(+)@C60)*] to produce the triplet CS state (3)(C20H10(•+)/Li(+)@C60(•-)). The distance between two electron spins in the triplet CS state was estimated to be 10 Å from the zero-field splitting pattern observed by EPR measurements at 4 K. The triplet CS state decayed to the ground state via intramolecular back electron transfer (BET). The CS lifetime was determined to be 240 μs in benzonitrile at 298 K. The temperature dependence of the rate constant of BET afforded the reorganization energy (λ = 1.04 eV) and the electronic coupling term (V = 0.0080 cm(-1)). The long lifetime of triplet CS state results from the spin-forbidden BET process and a small V value.

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

“…[72] Corannulene can bind not only to C 60 , but also to Li + @C 60 to form a charge-transfer (CT) complex between C 20 H 10 and Li + @C 60 in the ground state through concave-convex p-p CT interactions. [73] This CT interaction between Li + @C 60 and corannulene is stronger than that between C 60 and corannulene. [73] Such a difference in CT interactions results from the stronger electron-acceptor ability of Li + @C 60 than that of C 60 .…”

“…[73] This CT interaction between Li + @C 60 and corannulene is stronger than that between C 60 and corannulene. [73] Such a difference in CT interactions results from the stronger electron-acceptor ability of Li + @C 60 than that of C 60 . The formation constant of the C 20 H 10 /Li + @C 60 complex (Figure 8 b) at the ground state was determined to be 1.9 10 m À1 , which was much smaller than that of other supramolecules composed of Li + @C 60 , but larger than that of the C 20 H 10 /C 60 complex (!…”

“…1 m À1 ). [73] Photoexcitation of the CT complex results in the formation of the singlet CS state with a short CS lifetime of 4.7 ns. In contrast to the short-lived singlet CS state, the long-lived triplet CS state (240 ms) was produced by intermolecular electron transfer from corannulene to 3 (Li + @C 60 )*.…”

Chiral Buckybowl Molecules

“…Unsubstituted buckybowls 1 and 2 are not chiral due to the presence of the reflection symmetry with respect to the mirror planes containing the rotational axis to show C 5v and C 3v symmetry, respectively. Introducing the addends may break the reflection symmetry to cause chirality, and alter their properties, such as bowl-to-bowl inversion [12][13][14][15][16][17][18][19][20][21][22], chirality [12,17,19,23], bowl depth [14,19,20], crystal structure [19,24,25], molecular recognition [2,26,27,51] and supramolecular assembly [3,[28][29][30]52,53] behavior, metal complexation [23,[31][32][33][34][35][36], electronic conductivity [19,37,38], and so on. Although the chirality is an important element in three-dimensional curved π-electron systems, thus far there have been no reports of the enantioselective synthetic control of the bowl chirality.…”

“…Further extension of the π-conjugation of these chiral enantioenriched buckybowls leads to homochiral carbon nanotubes, and these chiral carbon materials create new perspectives in chiral catalysis, chiral sensing, chiral separation sciences, etc. [15][16][17][18][19][20][21][22][23][24][25][26][27]. A better understanding of bowl chirality will help researchers find a good way to control the chiral self-assembly of carbon nanotubes (CNTs) or fullerenes, which have already exhibited exciting potential as next-generation functional materials [28][29][30][31][32][33][34][35][36][37][38].…”