Theory of Singlet Fission in Polyenes, Acene Crystals and Covalently Linked Acene Dimers

Abstract

We report quadruple configuration interaction calculations within the extended Pariser$-$Parr$-$Pople Hamiltonian on the excited states of aggregates of polyenes, crystalline acenes, and covalently linked dimers of acene molecules. We determine the precise energy orderings and analyze the cluster wave functions in order to arrive at a comprehensive physical understanding of singlet fission in these diverse families of materials. Our computational approach allows us to retain a very large number of basis states and thereby obtain the correct relative energy orderings of one electron$-$one hole Frenkel and charge-transfer excitons versus intra- and intermolecular two electron$-$two hole triplet$-$triplet excited states. We show that from the energy orderings it is possible to understand the occurrence of singlet fission in polyene and acene crystals, as well as its near total absence in the covalently linked acene dimers. As in the acene crystals, singlet fission in the polyenes is a multichromophoric phenomenon, with the well-known 2${}^1$A${}_g^{-}$ playing no direct role. Intermolecular charge-transfer is essential for singlet fission in both acenes and polyenes, but because of subtle differences in the natures and orderings of the aggregate excited states, the mechanisms of singlet fission are slightly different in the two classes. We are thus able to give qualitative physical reasoning for the slower singlet fission in the polyenes, relative to that in crystalline pentacene. Our work also gives new insight into the complex exciton dynamics in tetracene crystals, which has been difficult to understand theoretically. Our large-scale many-body calculations provide us with the ability to understand the qualitative differences in the singlet fission yields and rates between different classes of $\pi$-conjugated materials.

20 pages, 10 figures (including Table of Contents, Scheme 1 and two figures in the Supporting Information)

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Cited by in corpus (14)

• Manipulating matter with strong coupling: harvesting triplet excitons in organic exciton microcavities
• Origins of singlet fission in solid pentacene from an ab initio Green's-function approach
• Magnetic dipolar interaction between correlated triplets created by singlet fission in tetracene crystals
• Theory of Primary Photoexcitations in Donor-Acceptor Copolymers
• Coherent dynamics of singlet fission controlled by nonlocal electron-phonon coupling
• Diagrammatic Exciton Basis Theory of the Photophysics of Pentacene Dimers
• Optical projection and spatial separation of spin entangled triplet-pairs from the S1 (21Ag-) state of pi-conjugated systems
• Inverse molecular design from first principles: tailoring organic chromophore spectra for optoelectronic applications
• A model Exact Study of the properties of low-lying electronic states of Perylene and Substituted Perylenes
• Higher energy triplet-pair states in polyenes and their role in intramolecular singlet fission
• Beating maps of singlet fission: Full-quantum simulation of coherent two-dimensional electronic spectroscopy in organic aggregates
• Wavefunction-Based Analysis of Dynamics Versus Yield of Free Triplets in Intramolecular Singlet Fission
• Exact Wave Packet Dynamics of Singlet Fission in Unsubstituted and Substituted Polyene Chains within Long-Range Interacting Models
• Optimisation of ultrafast singlet fission in 1D rings towards unit efficiency