FIGURE 1. Light bending and stretching.

Simmons et al.¹ make the conductivity of carbon nanotubes responsive to light by adding molecules of the azo-based Disperse Red 1 dye to the nanotube walls. These dye molecules undergo photoisomerization, with their molecular conformation shifting around their central nitrogen double bond: from the trans to the cis form under ultraviolet light of wavelength 254 nm, and back again under blue light of 365 nm. The changes cause significant, reversible shifts in the molecules' electrical dipole moments (unit: debye, D; arrows indicate direction), and thus in the electrical conductance of a nanotube transistor as a whole.