Photoinduzierte Valenzisomerisierungen von zwitterionischen s-Triazolo[4,3-b]pyridazinen

✍ Scribed by Prof. Dr. H.-J. Timpe; Dipl.-Chem. R. Burggraf; U. Lammel

• Publisher: John Wiley and Sons
• Year: 1981
• Tongue: English
• Weight: 543 KB
• Volume: 323
• Category: Article
• ISSN: 1615-4150
• DOI: 10.1002/prac.19813230415

✦ Synopsis

Photochemically Induced Valence Bond Tautomerism of Mesoionic s‐Triazolo[4,3‐b]pyridazines

The mesoionic s‐triazolo[4,3‐b]pyridazines 1–8 possess intensive charge‐transfer transitions, whose positions been influenced by the solvents. Some mesoionics fluoresce weakly. The irradiation gives valence isomers with a diaziridin ring. These products react under additional light irradiation to open‐chain ketenes, which incorporate methanol. The quantum yields of the valence bond tautomerism are between 0.08 to 0.45. They depend on the irradiation wavelength, the solvents and the substituents in the pyridazine‐part of the molecule. Because the oxygen‐insensibility and the sensibilisation with benzene and fluorene been supposed that these reaction take place in the S~1~‐state. The photoreaction of the valence isomer 9 of the mesoion 1 have a quantum yield of 0.13.