Triplet excitation transfer in glassy systems: spatial and spectral diffusion

Area of Science:

• Photochemistry
• Solid-state physics
• Molecular dynamics

Background:

• Triplet excitation transfer is crucial for understanding energy dynamics in molecular systems.
• Benzophenone serves as a model chromophore for studying excitation transport in glassy matrices.
• Inhomogeneous broadening in glassy media complicates the analysis of energy transfer processes.

Purpose of the Study:

• To investigate triplet excitation transfer mechanisms in benzophenone-doped 2-methyltetrahydrofuran.
• To analyze the role of exchange interaction and site disorder in energy transport.
• To determine the influence of excitation hopping on spectral diffusion and thermalization.

Main Methods:

• Emission spectroscopy to monitor excited states.
• Optical depolarization measurements as a function of wavelength and time.
• Analysis of optical anisotropy to quantify excitation localization.

Main Results:

• Observed a factor of 2 decrease in anisotropy from high to low energies, indicating hopping-mediated thermalization.
• Excitons did not reach steady-state energies within their lifetime, but solvation effects were observable.
• Short-time transfers (approx. 1 nm hops) contributed less to spectral diffusion than later transport.

Conclusions:

• Spatially correlated site energies are suggested at short distances (around 1 nm).
• The findings challenge assumptions about the dominant role of short-time hops in spectral diffusion.
• Solvation dynamics play a role in observing excited-state energy levels within exciton lifetimes.