Novel sulfenate derivatives and their bioconjugates for phototherapy of tumors and other lesions. The sulfenates of the present invention are designed to absorb low-energy ultraviolet, visible, or near-infrared (NIR) region of the electromagnetic spectrum. The phototherapeutic effect is caused by direct interaction of free radicals, the reactive intermediate produced upon photofragmentation of the sulfenate moiety, with the tissue of interest.