Energy versus Electron Transfer: Controlling the Excitation Transfer in Molecular Triads

Abstract

The photochemistry of Ru coordination compounds is generally discussed to originate from the lowest lying triplet metal-to-ligand charge-transfer state ( MLCT). However, when heteroleptic complexes are considered, for example, in the design of molecular triads for efficient photoinduced charge separation, a complex structure of MLCT states, which can be populated in a rather narrow spectral window (typically around 450 nm) is to be considered. In this contribution we show that the localization of MLCT excited states on different ligands can affect the following ps to ns decay pathways to an extent that by tuning the excitation wavelength, intermolecular energy transfer from a Ru -terpyridine unit to a fullerene acceptor can be favored over electron transfer within the molecular triad. These results might have important implications for the design of molecular dyads, triads, pentads and so forth with respect to a specifically targeted response of these complexes to photoexcitation.

Characterizing photocatalysts for water splitting: from atoms to bulk and from slow to ultrafast processes

“…141,144 This is widely used to assign spectral signatures of formation photooxidation and -reduction reactions 168 and of charge separated states in transient absorption spectroscopy. [169][170][171][172] UV/vis-SEC delivers the absorption spectra of the oxidized/reduced donor/acceptor and allows to model the transient spectra to be observed if charge separation occurs and even can be used to quantify charge separation in donor acceptor systems. 173 Applying rR analysis in combination with TD-DFT calculations allows to identify the structural subunit, which is reduced or oxidized and to reveal structural changes upon reduction or oxidation via shifts in the vibrational frequencies.…”

Extending Long‐lived Charge Separation Between Donor and Acceptor Blocks in Novel Copolymer Architectures Featuring a Sensitizer Core

“…In both cases the light‐induced charge separation proceeds primarily via oxidative quenching to transfer an electron first to the acceptor chain and subsequently to regenerate the active photosensitizers by secondary electron transfer from the donor chain. Although the linkage pattern is reversed among both triads, which may affect the kinetics of initial oxidative quenching, the recombination of the fully charge separated state depends on the overall distance of the oxidized donor and reduced acceptor units, which would be the same again for both triads. Based on this hypothesis, the observed difference in recombination is interpreted in terms of the different nature of the donor chains.…”

Superexchange in the fast lane – intramolecular electron transfer in a molecular triad occurs by conformationally gated superexchange

“…Temperature dependence of ET1 Figure S8) for which identical PTZ donor, donor-acceptor distance and chemical linkage are involved, Table S6 indicates very similar -ΔG values for 1-3 which vary by only 10% from 0.26 (2) to 0.23 (1). Likewise, λ is rather similar for 1 (0.67 eV) and 2 (0.63 eV).…”

“…The synthesis, steady-state emission spectra, electrochemical properties and photoinduced dynamics of 1-3 at room temperature have been reported elsewhere. [1][2][3] Time-Resolved Spectroscopy. Femtosecond (fs) transient absorption (TA) spectra were collected by using a previously reported home-built pump-probe laser system which is based on an amplified Ti:…”

“…Relaxation processes for 1-3 which refer to the model proposed at room temperature. 1,2 Terpyridine (tpy) ligand connected with N-methylphenothiazine (PTZ) and fullerene (C 60 ) are named as PTZ-tpy and tpy-C 60 , respectively. Excitation of Ru(tpy) 2 photosensitizer generates two differently distributed MLCT states, i.e.…”