Sharing Orbitals:  Ultrafast Excited State Deactivations with Different Outcomes in Bucky Ferrocenes and Ruthenocenes

Abstract

We report on the singlet ground and singlet/triplet excited-state features of a series of bucky ferrocenes, bucky ruthenocenes, and respective reference compounds. In the bucky ferrocene conjugates, intimate contacts between the fullerenes and ferrocenes result in appreciable ground-state interactions-suggesting a substantial shift of charge density from the electron donor (i.e., ferrocene) to the electron acceptor (i.e., fullerene). In contrast, no prominent charge-transfer features were observed for the bucky ruthenocene conjugates. An arsenal of experimental techniques, ranging from fluorescence (i.e., steady state and time-resolved) and pump probe experiments (i.e., femtosecond and nanoseconds) to pulse radiolysis, were employed to examine excited-state interactions. In the excited states, bucky ferrocene conjugates are dominated by rapid charge separation reactions (0.8 +/- 0.1 ps) to yield metastable radical ion pairs. The radical ion pair lifetimes vary between 27 and 39 ps. No charge separation was, however, found in the corresponding bucky ruthenocence. Instead, an intrinsically faster excited-state deactivation (approximately 200 ps) evolves from the heavier ruthenium center-relative to iron. This effect is further augmented by the unfavorably shifted oxidation potential in ruthenocene of about 0.61 V, which in ruthenocene (-deltaG(ET) = -0.26 eV), in contrast to ferrocene (-deltaG(ET) = 0.35 eV), renders charge separation thermodynamically unfeasible.

Strategies for Stabilizing Atomically Dispersed Metal Catalysts

“…In addition to forming σ‐bonds, metal atoms can interact with carbon‐based materials through M–π interactions. Similar to the binding in ferrocene, atomically dispersed Fe atoms are also present in bucky ferrocenes and confined in single‐wall carbon nanotubes (SWCNTs) . The atomically dispersed Fe atoms effectively catalyze CC bond reorganization and fabricated new CC networks.…”

Synthesis, Aromaticity and Photophysical Behaviour of Ferrocene‐ and Ruthenocene‐Appended Semisynthetic Chlorin Derivatives

“…[21] Theire xcellent energy-and charge-transfer capability make them advantageousi nm imicking photosyntheticp rocesses. [22] Strong electron donors,s uch as ferrocenes (Fcs) and ruthenocenes (Rcs),a re often conjugated in the vicinity of electron-accepting moieties [23,24] or used as components to improve charge-transfer properties of biomimetic systems. [25,26] From as ynthetic perspective,F cm oieties have been attachedt ov arious chromophores through well-established syntheticr outes.…”

A Ruthenium Bridge in Fullerene–Ferrocene Arrays: Synthesis of [Ru(C60Me5)R(CO)2] (R=C6H4Fc, C≡CFc) and Their Charge‐Transfer Properties

“…We asked ourselves the question about the photophysical behavior of a compound in which a metal atom is bonded to the fullerene in an η 5 ‐π manner 9. 10 Does the metal atom act as a mediator, a suppresser, or cause unexpected behavior? Another motivation for this investigation concerns the wide diversity of η 5 ‐π‐fullerene–metal complexes relative to the numerous organometallic compounds containing fullerene in which the metal and the fullerene moieties are connected but also separated by organic groups, as exemplified by the well‐known fulleropyrrolidine unit 11.…”