Gerald Giller

PHASE CHANGE OF 1,4-DITHIOKETO-3,6-DIPHENYL-PYRROLO-3,4-C-PYRROLE FOR INFORMATION STORAGE APPLICATIONS

Three crystal modifications I, II, and III are known to exist for 1,4‐dithioketo‐3,6‐diphenyl‐pyrrolo‐[3,4‐c]‐pyrrole (DTPP; blue pigment). Among these, only modification III exhibits an intense near‐IR absorption due to interplanar π‐π interactions of the alternating nitrogen and thiocarbonyl carbon atoms along the stacking axis. An optical information storage system of the ‘‘write once’’ type has been developed in which the near‐IR absorption (‘‘on’’ state) is switched‐off (‘‘off’’ state) on irradiation with GaAs laser diodes in the presence of a hydrazone compound. The near‐IR absorption ceases to exist due to a molecular rearrangement caused by laser‐generated vapors of hydrazone molecules. X‐ray‐diffraction analysis revealed that the present phenomenon is due to the phase change from modification quasi‐III to modification II. The optical disk (structure: substrate/hydrazone/DTPP/Al) exhibits a reflectivity change from about 30% to 45% on writing with a power of about 9 mW at 780 nm.