Vibronic Effects in the Ultrafast Interfacial Electron Transfer of Perylene-Sensitized TiO₂ Surfaces

Abstract

We combine ultrafast transient absorption (TA) spectroscopy and nonadiabatic quantum dynamics simulations to describe the real-time unfold of vibronic effects on the photoabsorption of TiO 2 anatase sensitized with the (perylen-9-yl)carboxylate dye (Pe-COOH/TiO 2 ). The excited state is mapped in time and frequency by ultrafast broadband spectroscopy while atomistic quantum dynamics is used to simulate the self-consistent vibronic effects. The TA map shows the lifetime of the electronic population generated in the S 1 state of the dye and the rise of the absorption D 0 −D 1 of the cation. The theoretical analysis reveals that the electron transfer from perylene into TiO 2 is complete within 20 fs, in agreement with the 12 fs experimental measurement. Because of the structural relaxation produced by the photoinduced electron transfer, the optical gap decreases by 390 meV, in agreement with the D 0 −D 1 transition band. Furthermore, the reorganization energy estimated to be around 220 meV is mostly due to the energy shift of the HOMO level, since the electron transfer occurs in the wide-band limit with little dependence on reorganization energy modes. By assuming the Condon approximation and by making use of the mixed quantum/classical trajectories of the Pe-COOH/TiO 2 system, the absorption spectrum is calculated, and the broad features of the transient absorption spectrum are correlated to excited-state nuclear reorganization effects of the adsorbate dye. The reorganization energy modes are identified by the power spectrum of the velocity autocorrelation function, which shows the occurrence of nonequilibrium modes within the range 1000−1800 cm −1 as in-plane asymmetric C−C vibrations in the perylene dye. The vibrational modes with the strongest influence on the optical gap contribute to shifting the absorption spectrum up in energy by ∼2000 cm −1 . The overall agreement between theory and experiment reveals the capabilities of both methods to study vibronic effects in molecular and extended systems.

Dye-sensitized solar cells strike back

“…83 In a related study, excited-state injection by (perylene-9yl)carboxylate into TiO 2 was shown to be complete within 12 fs. 84 The ultrafast transient absorption data mapped the decay of the singlet excited state and the appearance of the oxidized perylene. Nonadiabatic quantum dynamic simulations indicated that injection was complete within 20 fs, in close agreement with the experimental value.…”

“…The agreement between theory and experiment in these studies indicates that these are powerful tools for quantifying vibronic effects at dye-sensitized interfaces. 84 2.6.2 Sensitizer regeneration. Upon excited-state injection the oxidized sensitizer is reduced by an electron donor present in the electrolyte in a process known as sensitizer regeneration.…”

“…The agreement between theory and experiment in these studies indicates that these are powerful tools for quantifying vibronic effects at dye-sensitized interfaces. 84 …”

Crystal Symmetry and Static Electron Correlation Greatly Accelerate Nonradiative Dynamics in Lead Halide Perovskites

“…Multiple NA-MD studies of bulk perovskites have been undertaken to date, providing insight into the role of cation and halide identity, symmetry breaking at grain boundaries, and vacancies in determining the kinetics of such processes. Other works have reported NA-MD studies of the nonradiative hot carrier relaxation and electron–hole recombination processes in perovskite nanocrystals, 2D perovskites, − and related heterostructure systems. − Currently, NA-MD simulations of complex systems such as condensed phase or nanoscale materials, including lead halide perovskites (LHPs), rely on the use of a single-particle (SP) description of the electronic excited states. − Within this description, the Coulomb and exchange interactions between electrons and holes are neglected, and the electrons and holes are considered free particles.…”

Conformational and Binding Effects on Interfacial Electron Transfer from Dual-Linker Sensitizers

“…Differential absorption (Δ mOD) was detected via a 5 kHz chopper, a home-built high-throughput prism polychromator, and a 10 kHz line-scan camera enabling shot-to-shot referencing. IET from several perylene chromophores substituted with different single linkers in the peri position has been investigated by us. , Measured IET times ranged from around 12 fs for a directly bound carboxylic acid linker (Pe-COOH) to 100 fs for a saturated propionic acid linker. Therefore, high time resolution is required for the experiment.…”