Coherent exciton-vibrational dynamics and energy transfer in conjugated organics

Abstract

Coherence, signifying concurrent electron-vibrational dynamics in complex natural and man-made systems, is currently a subject of intense study. Understanding this phenomenon is important when designing carrier transport in optoelectronic materials. Here, excited state dynamics simulations reveal a ubiquitous pattern in the evolution of photoexcitations for a broad range of molecular systems. Symmetries of the wavefunctions define a specific form of the non-adiabatic coupling that drives quantum transitions between excited states, leading to a collective asymmetric vibrational excitation coupled to the electronic system. This promotes periodic oscillatory evolution of the wavefunctions, preserving specific phase and amplitude relations across the ensemble of trajectories. The simple model proposed here explains the appearance of coherent exciton-vibrational dynamics due to non-adiabatic transitions, which is universal across multiple molecular systems. The observed relationships between electronic wavefunctions and the resulting functionalities allows us to understand, and potentially manipulate, excited state dynamics and energy transfer in molecular materials.

Vibronic coherence contributes to photocurrent generation in organic semiconductor heterojunction diodes

“…The results clearly indicate a coherent charge transfer process within 200 fs of the excitation, that has a significant contribution to the photocurrent in the Ternary (H) device. It has been suggested that there is strong coupling between electronic potential energy and the torsional mode, which facilitates the initial coherent excitation energy transfer (EET) (<100 fs) and charge separation process 13,14 . Transient results demonstrate that the simultaneous process of EET from the excited state is significant in the Ternary (L) and D1:A1 blend, compared to the Ternary (H) blend ( Supplementary Fig.…”

“…Nevertheless, the presence of other ultrafast processes (coherent intrachain energy transfer etc.) can contribute to the charge separation in the nanoscale systems [12][13][14] . However, a definitive correlation of oscillatory signals at femtosecond timescale to the charge separation and photocurrent generation is still lacking.…”

Ultrafast Exciton Self‐Trapping and Delocalization in Cycloparaphenylenes: The Role of Excited‐State Symmetry in Electron‐Vibrational Coupling

“…Forschungsartikel directions of derivative coupling,two optical transitions were employed to develop distinctive excited-state geometries in terms of torsional disorders via excited-state symmetrydependent electron-vibrational coupling. [29] Although the symmetry of electronic wavefunctions at non-adiabatic regions cannot be definitely determined owing to intrinsic structural disordering,q uasi-cyclic and symmetric structures of [n]CPPs may maintain quasi-(anti)symmetric characters of excited-state wavefunctions at non-adiabatic regions.H ereafter, we employ the term "(anti)symmetric-like" to roughly characterize the excited-states.A fter the completion of nonadiabatic transitions from the two high-lying excited states to the lowest excited state,e xciton (de)localization was comparatively investigated until the energy minimum structure of S 1 state was achieved with the aid of slow torsional motions, which is called torsional relaxation. With respect to ultrafast torsional reorganizations and torsional relaxations,the extent of exciton (de)localization was analyzed by time-resolved fluorescence measurements.…”

The Potential of EuPRAXIA@SPARC_LAB for Radiation Based Techniques

“…Another kind of applications that would largely benefit from the peculiar features of the EuPRAXIA@SPARC_LAB FEL radiation is represented by the wide class of experiments aimed at studying the interaction of intense radiation pulses with molecules. How organic and biological molecules redistribute the energy of absorbed light is indeed a key fundamental question in organic chemistry and biology which time-resolved experiment can help to settle [62][63][64][65][66][67]. This class of experiments will help understanding the basic mechanisms of photo-protection/damage of amino acids [68], proteins and DNA/RNA [69].…”