The present invention relates to the use of thiazolyl-pyridinium based dyes in optical layers for optical data recording, preferably for optical data recording using a laser with a wavelength up to 450 nm.The invention further relates to a write only read many (WORM) type optical data recording medium capable of recording and reproducing information with radiation of blue laser, which employs a thiazolyl-pyridinium based type dye in the optical layer.The present invention further relates to new thiazolyl-pyridinium based dyes, of formula (V), (VI) or (VIII).