A novel metalloviologen complex {[Cd(PhSQ)(HTBC)(H₂O)₂]·1.25H₂O}_n (1) based on N-(4-sulfo- phenyl)-4,4΄-bipyridinium (PhSQ) and monoprotonated trimesic acid (HTBC) has been prepared and structurally characterized. Complex 1 has been characterized by elemental analysis, IR, thermogravimetric analyses, UV-Vis spectra and X-ray crystallography. The coordination geometry of Cd(II) ion is a pentagonal bipyramid. Complex 1 displays a zigzag chain along the b axis, and such chains are extended into a 2D layer supramolecular network through hydrogen bonding and π…π interactions. Moreover, complex 1 exhibits reversible photochromic and switchable luminescent behaviors via UV light irradiation at room temperature induced by the photogenerated radicals via a photo-induced electron transfer (PET) mechanism.