Picosecond timescale tracking of pentacene triplet excitons with chemical sensitivity

Abstract

Singlet fission is a photophysical process in which an optically excited singlet exciton is converted into two triplet excitons. Singlet fission sensitized solar cells are expected to display a greatly enhanced power conversion efficiency compared to conventional singlejunction cells, but the efficient design of such devices relies on the selection of materials capable of harvesting triplets generated in the fission chromophore. To this aim, the possibility of measuring triplet exciton dynamics with chemical selectivity paves the way for the rational design of complex heterojunctions, with optimized triplet conversion. Here we exploit the chemical sensitivity of X-ray absorption spectroscopy to track triplet exciton dynamics at the picosecond timescale in multilayer films of pentacene, the archetypal singlet fission material. We experimentally identify the signature of the triplet exciton in the Carbon K-edge absorption spectrum and measure its lifetime of about 300 ps. Our results are supported by state-of-the-art ab initio calculations.

Spin adapted implementation of EOM-CCSD for triplet excited states: Probing intersystem crossings of acetylacetone at the carbon and oxygen K-edges

“…From the experimental point of view, the core-to-SOMO peaks are a preferred choice when tracking excited-state dynamics, since they unambiguously originate from the valence-excited states that are probed. 5,11,12,38 Other mechanisms can of course also occur, see e.g. the right scheme in Fig.…”

“…Particularly relevant for the present work is the recent development of coupled cluster approaches to near-edge timeresolved X-ray absorption spectroscopy (TR-XAS). 5,[11][12][13][14] In this contribution we broaden the spin adapted equation of motion coupled cluster singles and doubles (EOM-CCSD) approach 15,16 to the calculation of triplet transient state X-ray absorption spectra. Several popular quantum chemistry codes contain algorithms for the solution of the coupled cluster right and left eigenvalue equations for singlet excited states in both spin-adapted and unrestricted formulations.…”

Time-resolved near-edge X-ray absorption fine structure of pyrazine from electronic structure and nuclear wave packet dynamics simulations

“…Now TR-XAS with microsecond to picosecond resolutions is routinely used to study crystals, bulk amorphous materials and molecules in liquids. [7][8][9][10][11] Using TR-XAS with sub-picosecond resolution to study the light-induced spin switching dynamics in an iron(II)-based complex in aqueous solution has been a) Electronic mail: shotatsuru101233@gmail.com b) Electronic mail: kbmo@kemi.dtu.dk c) Electronic mail: soco@kemi.dtu.dk reported. 12 In parallel to the advances at synchrotrons, X-ray free electron lasers (XFELs) were developed.…”

Tracking ultrafast reactions in organic materials through vibrational coherence: vibronic coupling mechanisms in singlet fission

“…Even so, the core problem remains that the structural data extracted from such optical experiments will only capture a limited portion of the phase space described by simulations. While we anticipate further improvement in this regard, it is likely the biggest breakthroughs will come from new spectroscopic techniques using ultrafast x-ray absorption, free-electron lasers or femtosecond electron diffraction that can directly monitor structural dynamics in real time following photoexcitation [167][168][169][170]. Such methods would offer an entirely new level of insight into the correlated electronic and nuclear dynamics and singlet fission and provide even more rigorous validation of vibronic models.…”