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Microscopic model of the optical absorption of carbon nanotubes functionalized with molecular spiropyran photoswitches


E. Malic, C. Weber, M. Richter, V. Atalla, T. Klamroth, P. Saalfrank, S. Reich, and A. Knorr

Phys. Rev. Lett. 106 (2011), 097401


Abstract: The adsorption of molecules to the surface of carbon nanostructures opens a new field of hybrid systems with distinct and controllable properties. We present a microscopic study of the optical absorption in carbon nanotubes functionalized with molecular spiropyran photo-switches. The switching process induces a change in the dipole moment leading to a significant coupling to the charge carriers in the nanotube. As a result, the absorption spectra of functionalized tubes reveal a considerable red-shift of transition energies depending on the switching state of the spiropyran molecule. The performed calculations bring new insights into the infuence of attached molecules on the optical properties of nanotubes - depending on the molecular dipole moment, dipole orientation, and molecule distribution. Our results suggest that carbon nanotubes are excellent substrates for the optical read-out of spiropyran-based molecular switches. The gained insights can be applied to other non-covalently functionalized one-dimensional nanostructures in an externally induced dipole field.