We report first-principles calculations of the electronic and transport properties of diarylethene molecules sandwiched between metallic armchair (5, 5) carbon nanotubes with open and closed configurations. The calculated transmission spectra of two configurations are distinctively different near the Fermi level, and their profiles can be tuned by the gate bias voltage. The on-off ratio of currents between the closed and open configurations under a gate bias voltage is predicted to be more than two orders of magnitude, which reproduces the essential features of the experimental results. Moreover, we find that the switching property of diarylethene molecular junctions is very robust to the anchoring configuration, substituent of cyclopentene, and choice of electrodes. (C) 2009 Elsevier B.V. All rights reserved.