Carbon nanotubes as substrates for molecular spiropyran-based switches

• Published in: Journal of physics. Condensed matter 2012-10, Vol.24 (39), p.394006-394006
• Main Authors: Malic, E, Setaro, A, Bluemmel, P, Sanz-Navarro, Carlos F, Ordejón, Pablo, Reich, S, Knorr, A
• Format: Article
• Language: English
• Subjects: Carbon nanotubes; Condensed matter; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Coupling (molecular); Density; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Electronic transport in multilayers, nanoscale materials and structures; Exact sciences and technology; Excitation; Nanostructure; Nanotubes; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures; Physics; Spiropyrans; Switches
• ISSN: 0953-8984; 1361-648X
• DOI: 10.1088/0953-8984/24/39/394006

We present a joint theory-experiment study investigating the excitonic absorption of spiropyran-functionalized carbon nanotubes. The functionalization is promising for engineering switches on a molecular level, since spiropyrans can be reversibly switched between two different conformations, inducing a distinguishable and measurable change of optical transition energies in the substrate nanotube. Here, we address the question of whether an optical read-out of such a molecular switch is possible. Combining density matrix and density functional theory, we first calculate the excitonic absorption of pristine and functionalized nanotubes. Depending on the switching state of the attached molecule, we observe a red-shift of transition energies by about 15 meV due to the coupling of excitons with the molecular dipole moment. Then we perform experiments measuring the absorption spectrum of functionalized carbon nanotubes for both conformations of the spiropyran molecule. We find good qualitative agreement between the theoretically predicted and experimentally measured red-shift, confirming the possibility for an optical read-out of the nanotube-based molecular switch.