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)

References in corpus (4)

• Morphology Effectively Controls Singlet-Triplet Exciton Relaxation and Charge Transport in Organic Semiconductors
• Quantitative calculations of the excitonic energy spectra of semiconducting single-walled carbon nanotubes within a $\pi$-electron model
• Photophysics of charge-transfer excitons in thin films of π-conjugated polymers
• Does Singlet Fission Enhance the Performance of Organic Solar Cells?

Cited by in corpus (6)

• Origins of singlet fission in solid pentacene from an ab initio Green's-function approach
• Diagrammatic Exciton Basis Theory of the Photophysics of Pentacene Dimers
• Inverse molecular design from first principles: tailoring organic chromophore spectra for optoelectronic applications
• 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
• Optimisation of ultrafast singlet fission in 1D rings towards unit efficiency