Spectral Diffusion of Excitons in 3,4,9,10-Perylenetetracarboxylic-diimide (PTCDI) Thin Films

In this work, we study spectral diffusion of molecular excitons in thin films of 3,4,9,10-perylenetetracarboxylic-diimide by using two-dimensional electronic spectroscopy (2DES). Temperature dependence of the spectral diffusion is studied from 105 to 471 K by analyzing the center line slope (CLS) of the ground-state bleach in the 2DES signal. A significant acceleration of the decay of the CLS with increasing the temperature is observed, which cannot be explained by a linear system-bath coupling model with a harmonic bath. We propose an anharmonic coupling model as the underlying mechanism, in which the exciton energy gap fluctuations by a high-frequency intramolecular vibration are enhanced by coupling with a low-frequency phonon mode.

Automated summary

The spectral diffusion of molecular excitons in thin films of 3,4,9,10-perylenetetracarboxylic-diimide was studied using two-dimensional electronic spectroscopy (2DES) in this work. The temperature dependence of the spectral diffusion was analyzed by studying the center line slope (CLS) of the ground-state bleach in the 2DES signal, revealing a significant acceleration of the decay of the CLS with increasing temperature. An anharmonic coupling model was proposed to explain this phenomenon, suggesting that exciton energy gap fluctuations are enhanced by coupling with low-frequency phonon modes.