Crossover from Single-Step Tunneling to Multistep Hopping for Molecular Triplet Energy Transfer

Abstract

Triplet energy transfer (TT), a key process in molecular and organic electronics, generally occurs by either strongly distance-dependent single-step tunneling or weakly distance-dependent multistep hopping. We have synthesized a series of pi-stacked molecules consisting of a benzophenone donor, one to three fluorene bridges, and a naphthalene acceptor, and studied the rate of TT from benzophenone to naphthalene across the fluorene bridge using femtosecond transient absorption spectroscopy. We show that the dominant TT mechanism switches from tunneling to wire-like hopping between bridge lengths 1 and 2. The crossover observed for TT can be determined by direct observation of the bridge-occupied state.

Quantitative generation of cation radicals and dications using aromatic oxidants: effect of added electrolyte on the redox potentials of aromatic electron donors

“…The equilibrium concentrations of the species in eqs (8) and (9) can be determined from the equations of chemical equilibria and equations of mass and charge balance (eqs (11)(12)(13)(14)(15)) combined into a cubic equation of one variable (eq. (16)) in terms of oxidant concentration [Ox +• ], which can be solved either analytically or numerically.…”

Theory of quantum energy transfer in spin chains: Superexchange and ballistic motion

“…We find that for short chains the coherent-superexchange contribution, resulting from the transmission of low frequency modes across the bridge, dominates the current. In contrast, for long chains resonant conduction is more significant, though the population of bath modes matching the system gaps is small at low temper- with recent experiments of triplet energy transfer on π-stacked molecules, demonstrating that the turnover between tunneling and (resonant) diffusive mechanisms occurs between N =1 to 2 [40].…”

“…Here it is rigorously obtained in a first principle derivation, relaying on the timescale separation between subsystem dynamics and the baths' motion, irrespective of the details on the chain spectrum, the reservoir realization, and system-baths interaction form. We expect this general behavior to show itself in numerous systems, including organic and biological structures, exploring electronic [39,40] and vibrational [8] energy transmission.…”

Donor-acceptor electron transport mediated by solitons

“…(8) and (9) that the total electron probability is not conserved if the parameter γ a is a constant. We can address this problem by using instead a nonlinear coupling of the form γ a = A a | N+1 | 2 for the first equation and −iA a | N | 2 N+1 for the second one so that (8) …”

“…There is a large class of biological [1][2][3][4][5] systems and synthetic molecular systems [6][7][8][9], in which charges or excitons (molecular excitations) migrate from site to site through multiple sites embedded in a complex system. In many cases an electron transport takes place from a donor to an acceptor through some intermediate molecules or systems such as macromolecules or molecular bridges.…”