9 research outputs found
Exact quantum master equation for a molecular aggregate coupled to a harmonic bath
We consider a molecular aggregate consisting of identical monomers. Each
monomer comprises two electronic levels and a single harmonic mode. The
monomers interact with each other via dipole-dipole forces. The monomer
vibrational modes are bilinearly coupled to a bath of harmonic oscillators.
This is a prototypical model for the description of coherent exciton transport,
from quantum dots to photosynthetic antennae. We derive an exact quantum master
equation for such systems. Computationally, the master equation may be useful
for the testing of various approximations employed in theories of quantum
transport. Physically, it offers a plausible explanation of the origins of
long-lived coherent optical responses of molecular aggregates in dissipative
environments
Real-Time Observation of Multiexcitonic States in Ultrafast Singlet Fission Using Coherent 2D Electronic Spectroscopy
Singlet fission is the spin-allowed conversion of a spin-singlet exciton into a pair of spin-triplet excitons residing on neighbouring molecules. To rationalize this phenomenon, a multiexcitonic spin-zero triplet-pair state has been hypothesized as an intermediate in singlet fission. However, the nature of the intermediate states and the underlying mechanism of ultrafast fission have not been elucidated experimentally. Here, we study a series of pentacene derivatives using ultrafast two-dimensional electronic spectroscopy and unravel the origin of the states involved in fission. Our data reveal the crucial role of vibrational degrees of freedom coupled to electronic excitations that facilitate the mixing of multiexcitonic states with singlet excitons. The resulting manifold of vibronic states drives sub-100 fs fission with unity efficiency. Our results provide a framework for understanding singlet fission and show how the formation of vibronic manifolds with a high density of states facilitates fast and efficient electronic processes in molecular systems.This is the author accepted manuscript. The final version is available from NPG via http://dx.doi.org/10.1038/nchem.237
Real-time observation of multiexcitonic states in ultrafast singlet fission using coherent 2D electronic spectroscopy.
Singlet fission is the spin-allowed conversion of a spin-singlet exciton into a pair of spin-triplet excitons residing on neighbouring molecules. To rationalize this phenomenon, a multiexcitonic spin-zero triplet-pair state has been hypothesized as an intermediate in singlet fission. However, the nature of the intermediate states and the underlying mechanism of ultrafast fission have not been elucidated experimentally. Here, we study a series of pentacene derivatives using ultrafast two-dimensional electronic spectroscopy and unravel the origin of the states involved in fission. Our data reveal the crucial role of vibrational degrees of freedom coupled to electronic excitations that facilitate the mixing of multiexcitonic states with singlet excitons. The resulting manifold of vibronic states drives sub-100 fs fission with unity efficiency. Our results provide a framework for understanding singlet fission and show how the formation of vibronic manifolds with a high density of states facilitates fast and efficient electronic processes in molecular systems.This is the author accepted manuscript. The final version is available from NPG via http://dx.doi.org/10.1038/nchem.237
Vibrational Coherence Reveals the Role of Dark Multiexciton States in Ultrafast Singlet Exciton Fission
We use 2D electronic photon-echo spectroscopy to study ultrafast singlet exciton fission in pentacene. Our observations and analysis of vibronic coherences provide insight to the role played by dark multiexcitonic states in mediating fission
Vibrational Coherence Reveals the Role of Dark Multiexciton States in Ultrafast Singlet Exciton Fission
We use 2D electronic photon-echo spectroscopy to study ultrafast singlet exciton fission in pentacene. Our observations and analysis of vibronic coherences provide insight to the role played by dark multiexcitonic states in mediating fission