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

Abstract

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.

Quantum Coherent Phenomena in Energy Harvesting and Storage

“…The highly conjugated acene and isoprenoid molecules that undergo singlet fission can be conveniently tuned to examine how structure impacts singlet fission, including work examining effects from optical crystal packing in singlet fission, intramolecular singlet fission, how packing impacts on ground state coupling, and dependencies on chemical functionalization in diphenylhexatriene . How these dynamic nuclear structures and couplings change along a reaction coordinate is also of crucial importance, and this VSI highlights work examining the impact of dynamic vibrational coherences on transfer efficiency, as well as impacts of coupling between low and high frequency modes …”

“…In the development of our understanding of the possible uses of quantum coherences to increase light harvesting and energy conversion, experimental results aimed at probing the functional role of coherences have been crucial. These include 2-dimensional electronic spectroscopy (2DES), ,,, which is the leading experimental approach in this field, as well as ultrafast transient absorption spectroscopy ,,,, and femtosecond stimulated Raman spectroscopy. , This VSI includes a thoughtful review on 2DES, as well as several papers highlighting the ability to simulate 2DES measurements. ,, The role of careful experimental measurements such as temperature-dependent and magnetic field-dependent absorption and emission spectroscopy are critical in adding to our fundamental understanding. Recent breakthroughs have also come from advances in theoretical and computational methods, such as the ability to accurately simulate complex spectra from complex and heterogeneous chemical systems, as well as to model interactions between chromophores, polymers, and donor–acceptor complexes.…”

“…4 How these dynamic nuclear structures and couplings change along a reaction coordinate is also of crucial importance, and this VSI highlights work examining the impact of dynamic vibrational coherences on transfer efficiency, 5 as well as impacts of coupling between low and high frequency modes. 6 Other chemical systems examining the role of quantum coherences involving nuclear degrees of freedom include measurement of coherences during metal-to-ligand charge transfer in platinum complexes as depicted in Figure 1, 7 coherences involved with ligand-to-metal charge transfer in azurin, 8 and coherence impacts on excited state proton transfer in model dye molecules. 9 Dephasing and decoherence processes are of great importance in maintaining and manipulating quantum coherences.…”

“…20 In the development of our understanding of the possible uses of quantum coherences to increase light harvesting and energy conversion, experimental results aimed at probing the functional role of coherences have been crucial. These include 2-dimensional electronic spectroscopy (2DES), 6,16,21,22 which is the leading experimental approach in this field, as well as ultrafast transient absorption spectroscopy 1,14,15,20,7 and femtosecond stimulated Raman spectroscopy. 8,9 This VSI includes a thoughtful review on 2DES, as well as several papers highlighting the ability to simulate 2DES measurements.…”