Molecular orientation and photoswitching kinetics on single-walled carbon nanotubes by optical second harmonic generation

Electrical conduction through chromophore-functionalized nanotubes can be modulated by light with wavelengths expected to isomerize the chromophores. Here, we use second harmonic generation to directly measure the orientation and photoisomerization kinetics of azo-benzene chromophores on single-walled carbon nanotubes. We find a net chromophore orientation with an average chromophore tilt angle of 40° ± 3°. We show that this angle can be reduced effectively to zero with an applied corona field. Periodic illumination with unpolarized 495 nm light induces reversible trans-cis switching, enabling the extraction of switching time scales both with and without an applied electric field.