On the spectra and isomerization of azobenzene attached non-covalently to an armchair (8,8) single-walled carbon nanotube

The structure, energies, electronic spectra and thermal trans–cis isomerization of azobenzene (AB) attached non-covalently to the sidewall of CNT(8,8) were calculated using the ONIOM(B3LYP/6–31 + G*:UFF) level of theory. We found that some subtle differences existed between the structures of the attached AB and the isolated one. The combination of AB and CNT(8,8) favored in energy because of their negative interaction energies. The attached trans-AB (TAB) was more stable than the physisorbed cis-AB (CAB). The electronic spectrum calculations showed that the absorption wavelengths of the attached CAB were red-shifted for the lowest three singlet states. The trans–cis isomerization process of the AB attached non-covalently to the CNT(8,8) involved mainly the bending of CNN angle. The π–π interaction between AB and CNT(8,8) was found to restrain the trans-to-cis isomerization of AB, but had little influence on the cis-to-trans backward reaction.