Universal properties of quasi-one-dimensional excitons in semiconducting single-walled carbon nanotubes and $\pi$-conjugated polymers

Abstract

The nature of the primary photoexcitations in semiconducting single-walled carbon nanotubes (S-SWCNTs) is of strong current interest. We have studied the emission spectra of S-SWCNTs and two different $\pi$-conjugated polymers in solutions and films, and have also performed ultrafast pump-probe spectroscopy on these systems. The emission spectra relative to the absorption bands are very similar in S-SWCNTs and polymers, with redshifted photoluminescence in films showing exciton migration. The transient photoinduced absorptions (PAs) in SWCNTs and $\pi$-conjugated polymers are also remarkably similar, with a low energy PA${}_1$ and a higher energy PA${}_2$ in all cases. Theoretical calculations of excited state absorptions within a correlated $\pi$-electron Hamiltonian find the same excitonic energy spectrum for S-SWCNTs and $\pi$-conjugated polymers, illustrating the universal features of quasi-one-dimensional excitons in carbon-based $\pi$-conjugated systems. In both cases PA${}_1$ is an excited state absorption from the optically allowed exciton to a two-photon exciton that occurs below the continuum band threshold. PA${}_1$ therefore gives the lower limit of the binding energy of the lowest optical exciton. The binding energy of lowest exciton belonging to the widest S-SWCNTs with diameters $\ge$ 1 nm in films is 0.3--0.4 eV, as determined by both experimental and theoretical methods.

22 pages, 6 figures, 1 table

References in corpus (1)

• Electron-electron interaction effects on optical excitations in semiconducting single-walled carbon nanotubes

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• Elucidation of the electronic structure of semiconducting single-walled carbon nanotubes by electroabsorption spectroscopy
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