PHOTOPHYSICS AND PHOTOCHEMISTRY OF PLANAR ALKYLANTHRAQUINONES (THE 1-METHYL AND 1,4-DIMETHYL COMPOUNDS) STUDIED BY SUBPICOSECOND AND NANOSECOND LASER PHOTOLYSIS AS WELL AS STEADY-STATE PHOTOLYSIS

By means of subpicosecond and nanosecond laser photolysis of the title compounds (MAQ and DMAQ), it is concluded that both the lowest excited singlet and triplet states undergo intramolecular hydrogen-atom transfer and the corresponding excited biradicals thus generated yield 9-hydroxy-1,10-anthraquinone-1-methide from MAQ and 9-hydroxy-4-methyl-1,10-anthraquinone-1-methide from DMAQ. Although these methides are stable at 77 K, they revert to the original anthraquinones at a higher temperature than 77 K. In ethanol and EPA (diethyl ether−isopentane−ethanol in 5:5:2 volume ratio) at room temperature, furthermore, 313 or 366 nm steady-state photolysis reveals that 1-methyl-9,10-dihydroxyanthracene (MAQH2) is formed from MAQ irrespective of the excitation wavelength but 1,4-dimethyl-9,10-dihydroxyanthracene (DMAQH2) is formed from DMAQ only upon 313 nm excitation. Undoubtedly, the lowest excited triplet state of MAQ abstracts a hydrogen atom from ethanol generating the semiquinone radical followed by formati...