A molecular movie of ultrafast singlet fission

Abstract

The complex dynamics of ultrafast photoinduced reactions are governed by their evolution along vibronically coupled potential energy surfaces. It is now often possible to identify such processes, but a detailed depiction of the crucial nuclear degrees of freedom involved typically remains elusive. Here, combining excited-state time-domain Raman spectroscopy and tree-tensor network state simulations, we construct the full 108-atom molecular movie of ultrafast singlet fission in a pentacene dimer, explicitly treating 252 vibrational modes on 5 electronic states. We assign the tuning and coupling modes, quantifying their relative intensities and contributions, and demonstrate how these modes coherently synchronise to drive the reaction. Our combined experimental and theoretical approach reveals the atomic-scale singlet fission mechanism and can be generalized to other ultrafast photoinduced reactions in complex systems. This will enable mechanistic insight on a detailed structural level, with the ultimate aim to rationally design molecules to maximise the efficiency of photoinduced reactions.

Singlet fission in a hexacene dimer: energetics dictate dynamics

“…35,39 Experimental signatures of vibrational coherences have been detected using ultrafast vibrational and 2D electronic spectroscopy, where both inter-and intramolecular vibrational modes have been found to be important. [40][41][42][43][44] For incoherent triplet pair formation, the signature of vibrational mediation has been the dependence of the singlet ssion rate constant on the energetic driving force DE S-TT . This driving force increases with n, the number of rings in the oligoacene chromophore, such that tetracene (Tc, n ¼ 4) < pentacene (Pc, n ¼ 5) < hexacene (Hc, n ¼ 6).…”

Singlet Fission in Carbene‐Derived Diradicaloids

“…Two molecular families are promising: Polyacenes and diradicaloids. Until today, most of the SF materials are, however, built around the acene platform, that is, ubiquitous tetracene and pentacene as well as their derivatives . In stark contrast, investigations on diradicaloids remain hitherto largely restrained to computational studies .…”

Matrix Product State Simulations of Non-Equilibrium Steady States and Transient Heat Flows in the Two-Bath Spin-Boson Model at Finite Temperatures

“…This means that one is able to reverse the transformation and calculate thermal expectations for the actual bosonic bath such as . This is particularly useful for molecular systems in which environmental (vibrational) dynamics are also important observables that report on the mechanisms and pathways of physio-chemical transformations [ 38 , 39 , 40 ]. In this article, we will use this capability later to look at the non-equilibrium heat flows between the TLS and its environments.…”