A Metallofullerene Electron Donor that Powers an Efficient Spin Flip in a Linear Electron Donor–Acceptor Conjugate

The dream target of artificial photosynthesis is the realization of long-lived radical ion pair states that power catalytic centers and, consequently, the production of solar fuels. Notably, magnetic field effects, especially internal magnetic field effects, are rarely employed in this context. Here, we report on a linear Lu₃N@<i>I</i>_<i>h</i>-C₈₀–PDI electron donor–acceptor conjugate, in which the presence of the Lu₃N cluster exerts an appreciable electron nuclear hyperfine coupling on the charge transfer dynamics. As such, a fairly efficient radical ion pair intersystem crossing converts the initially formed singlet radical ion pair state, ¹[(Lu₃N@<i>I</i>_<i>h</i>-C₈₀)^•+–PDI^•–], to the corresponding triplet radical ion pair state, ³[(Lu₃N@<i>I</i>_<i>h</i>-C₈₀)^•+–PDI^•–]. Most notably, the radical ion pair state lifetime of the latter is nearly 1000 times longer than that of the former

Bidirectional Electron Transfer Capability in Phthalocyanine–Sc₃N@<i>I</i>_<i>h</i>–C₈₀ Complexes

To activate oxidative and/or reductive electron transfer reactions, <i>N</i>-pyridyl-substituted Sc₃N@<i>I</i>_<i>h</i>–C₈₀ (<b>4</b>) and C₆₀ (<b>3</b>) fulleropyrrolidines have been prepared and axially coordinated to electron-rich (<b>1</b>) or electron-deficient (<b>2</b>) Zn­(II)­phthalocyanines (Zn­(II)­Pcs) through zinc-pyridyl, metal–ligand coordination affording a full-fledged family of electron donor–acceptor ensembles. An arsenal of photophysical assays as they were carried out with, for example, <b>1</b>/<b>4</b> and <b>2</b>/<b>4</b> show unambiguously that a Zn­(II)­Pc-to-Sc₃N@<i>I</i>_<i>h</i>–C₈₀ photoinduced electron transfer takes place in the former ensemble, whereas a Sc₃N@<i>I</i>_<i>h</i>–C₈₀-to-Zn­(II)­Pc electron transfer occurs in the latter ensemble. To the best of our knowledge, this is the first time that a fullerene-based molecular building block shows an electron transfer dichotomy, namely acting both as electron-acceptor or electron-donor, and its outcome is simply governed by the electronic nature of its counterpart. In light of the latter, the present work, which involves the use of Sc₃N@<i>I</i>_<i>h</i>–C₈₀, one of the most abundant and easy-to-purify endohedral metallofullerenes, is, on one hand, a paradigmatic change and, on the other hand, an important milestone <i>en-route</i> toward the construction of easy-to-prepare molecular materials featuring switchable electron transfer reactivity

Stabilizing Ion and Radical Ion Pair States in a Paramagnetic Endohedral Metallofullerene/π‑Extended Tetrathiafulvalene Conjugate

Electron donor–acceptor conjugates of paramagnetic endohedral metallofullerenes and π-extended tetrathiafulvalene (exTTF) were synthesized, characterized, and probed with respect to intramolecular electron transfer involving paramagnetic fullerenes. UV–vis–NIR absorption spectroscopy complemented by electrochemical measurements attested to weak electronic interactions between the electron donor, exTTF, and the electron acceptor, La@C₈₂, in the ground state. In the excited state, photoexcitation powers a fast intramolecular electron transfer to yield an ion and radical ion pair state consisting of one-electron-reduced La@C₈₂ and of one-electron-oxidized exTTF

A Paradigmatic Change: Linking Fullerenes to Electron Acceptors

The potential of Lu₃N@C₈₀ and its analogues as electron acceptors in the areas of photovoltaics and artificial photosynthesis is tremendous. To this date, their electron-donating properties have never been explored, despite the facile oxidations that they reveal when compared to those of C₆₀. Herein, we report on the synthesis and physicochemical studies of a covalently linked Lu₃N@C₈₀–perylenebisimide (PDI) conjugate, in which PDI acts as the light harvester and the electron acceptor. Most important is the unambiguous evidencein terms of spectroscopy and kineticsthat corroborates a photoinduced electron transfer evolving from the ground state of Lu₃N@C₈₀ to the singlet excited state of PDI. In stark contrast, the photoreactivity of a C₆₀–PDI conjugate is exclusively governed by a cascade of energy-transfer processes. Also, the electron-donating property of the Lu₃N@C₈₀ moiety was confirmed through constructing and testing a bilayer heterojunction solar cell device with a PDI and Lu₃N@C₈₀ derivative as electron acceptor and electron donor, respectively. In particular, a positive photovoltage of 0.46 V and a negative short circuit current density of 0.38 mA are observed with PDI/Ca as anode and ITO/Lu₃N@C₈₀ as cathode. Although the devices were not optimized, the sign of the <i>V</i>_OC and the flow direction of <i>J</i>_SC clearly underline the unique oxidative role of Lu₃N@C₈₀ within electron donor–acceptor conjugates toward the construction of novel optoelectronic devices

A Paradigmatic Change: Linking Fullerenes to Electron Acceptors

The potential of Lu₃N@C₈₀ and its analogues as electron acceptors in the areas of photovoltaics and artificial photosynthesis is tremendous. To this date, their electron-donating properties have never been explored, despite the facile oxidations that they reveal when compared to those of C₆₀. Herein, we report on the synthesis and physicochemical studies of a covalently linked Lu₃N@C₈₀–perylenebisimide (PDI) conjugate, in which PDI acts as the light harvester and the electron acceptor. Most important is the unambiguous evidencein terms of spectroscopy and kineticsthat corroborates a photoinduced electron transfer evolving from the ground state of Lu₃N@C₈₀ to the singlet excited state of PDI. In stark contrast, the photoreactivity of a C₆₀–PDI conjugate is exclusively governed by a cascade of energy-transfer processes. Also, the electron-donating property of the Lu₃N@C₈₀ moiety was confirmed through constructing and testing a bilayer heterojunction solar cell device with a PDI and Lu₃N@C₈₀ derivative as electron acceptor and electron donor, respectively. In particular, a positive photovoltage of 0.46 V and a negative short circuit current density of 0.38 mA are observed with PDI/Ca as anode and ITO/Lu₃N@C₈₀ as cathode. Although the devices were not optimized, the sign of the <i>V</i>_OC and the flow direction of <i>J</i>_SC clearly underline the unique oxidative role of Lu₃N@C₈₀ within electron donor–acceptor conjugates toward the construction of novel optoelectronic devices