摘要 :
We develop a theory of the electronic structure and photophysics of interacting chains of π-conjugated polymers to understand the differences between solutions and films. While photoexcitation generates only the intrachain excito...
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We develop a theory of the electronic structure and photophysics of interacting chains of π-conjugated polymers to understand the differences between solutions and films. While photoexcitation generates only the intrachain exciton in solutions, the optical exciton as well as weakly allowed charge-transfer excitons are generated in films. We extend existing theories of the lowest polaron pair and charge-transfer excitons to obtain descriptions of the excited states of these interchain species, and we show that a significant fraction of ultrafast photoinduced absorptions in films originates from the lowest charge-transfer exciton. Our proposed mechanism explains the simultaneous observation of polaronlike-induced absorption features peculiar to films in ultrafast spectroscopy and the absence of mobile charge carriers as deduced from other experiments. We also show that there is a 1:1 correspondence between the essential states that describe the photophysics of single chains and of interacting chains that constitute thin films.
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摘要 :
We present a quantitative theory of optical absorption polarized transverse to the tube axes in semiconducting single-walled carbon nanotubes. Within one-electron theory, transverse optical absorption occurs at an energy that is e...
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We present a quantitative theory of optical absorption polarized transverse to the tube axes in semiconducting single-walled carbon nanotubes. Within one-electron theory, transverse optical absorption occurs at an energy that is exactly in the middle of the two lowest longitudinal absorption energies. For nonzero Coulomb interactions between the π electrons, transverse optical absorption is to an exciton state that is strongly blueshifted relative to the longitudinal excitons. Very similar behavior is observed in the π-conjugated polymer polyparaphenylenevinylene, where the optical absorption polarized predominantly perpendicular to the polymer chain axis is blueshifted relative to the absorptions polarized predominantly along the chain axis. The binding energy of the transverse exciton in the nanotubes is considerably smaller than those of the longitudinal excitons. Electron-electron interactions also reduce the relative oscillator strength of the transverse optical absorption. Our theoretical results are in excellent agreement with recent experimental measurements in four chiral nanotubes.
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