PHASE-CHANGE OF ,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- dithidketo-3,6-diphenyl-pyrrolo- [3,4-c]-pyrrole (DTPP; blue pigment). Among these, only modification III exhibits an intense near-IR absorp tion due to interplanar pi-pi interactions of the alternating nitrogen and thiocarbonyl carbon atoms along the stacking axis. An optical inf ormation 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 hy drazone compound. The near-IR absorption ceases to exist due to a mole cular rearrangement caused by laser-generated vapors of hydrazone mole cules. X-ray-diffraction analysis revealed that the present phenomenon is due to the phase change from modification quasi-III to modificatio n II. The optical disk ( structure: substrate/hydrazone/DTPP/Al) exhib its a reflectivity change from about 30% to 45% on writing with a powe r of about 9 mW at 780 nm.