Lifetime Broadening and Impulsive Generation of Vibrational Coherence Triggered by Ultrafast Electron Transfer

Abstract

The absorption bandshape of chromophores in liquid solution at room temperature is usually dominated by pure electronic dephasing dynamics, which occurs on the sub-100 fs timescale. Herein, we report on a series of dyads consisting of a naphtalenediimide (NDI) electron acceptor with one or two phenyl-based donors for which photoinduced intramolecular electron transfer is fast enough to be competitive with pure electronic dephasing. As a consequence, the absorption band of the π-π * transition of these dyads

Long-lived triplet charge-separated state in naphthalenediimide based donor–acceptor systems

“…This band broadening was recently shown to originate from the ultrafast decay of the NDI-centred π–π* excited state upon CS. 47 …”

“…The ultrafast CS dynamics of these dyads, measured by UV-Vis TA in ACN, were already discussed earlier. 47 In brief, CS takes place with an average time constant ranging from 30 to 200 fs, depending on Δ G CS and the number of Ds. CS accelerates with increasing driving force and is approximately twice as fast in the symmetric than the asymmetric dyads.…”

“…1A ). The oxidation potential of the phenyl-based Ds decreases from 1 to 4, allowing –Δ G CS , the driving force for charge separation (CS), to be varied from <0.35 to about 0.85 eV, 47 while keeping the coupling to the NDI core nearly constant. This series is compared with the reference NDI ( pNDI ), which is decorated with two innocent ethyl-hexyl (EH) linkers as well as to Vs with two non-aromatic and weakly coupled Ds 5.…”

Bridge-Length- and Solvent-Dependent Charge Separation and Recombination Processes in Donor–Bridge–Acceptor Molecules

“…Furthermore, the CDDs based on S 0 geometries are also shown in Figure S4. Additionally, the fluorescence lifetime gradually decreases with the growth of the B-linkage length in the same solvent because the oscillator intensity gradually increases with the increase of the B length during transition from the emitting state to the ground state ( f : 0.0459–0.5533–1.2625), indirectly indicating the weakening of the CT. , …”

“…Furthermore, the CDDs based on S 0 geometries are also shown in Figure S4. Additionally, the fluorescence lifetime gradually decreases with the growth of the B-linkage length in the same solvent because the oscillator intensity gradually increases with the increase of the B length during transition from the emitting state to the ground state (f: 0.0459−0.5533−1.2625), indirectly indicating the weakening of the CT. 67,68 To quantitatively compare the extent of CT between the D− nB−A systems, the Multiwfn program is employed to calculate the CT indices q and D CT , 63 where q represents the amount of charge transferred and D CT represents the CT distance, respectively. 66 The outputs show the q and D CT values of dyad B 0 to be 0.89 and 4.38 Å, respectively, which are larger than the corresponding values for B 1 (q = 0.47, D CT = 4.14 Å) and B 2 (q = 0.28, D CT = 1.69 Å), respectively.…”