Synthesis and Photochromic Behaviour of Naphthopyrans, Pyranoquinolines, Pyranoquinazolines and Pyranoquinoxalines

Article abstract of DOI:10.1002/hlca.19970800310

New chromenes annulated with different six-membered azaheterocycles were prepared, i.e., the 3H-pyrano[3,2-f]quinolines 9/10 and 14, the 8H-pyrano[2,3-h]isoquinoline 11, the 8H-pyrano[3,2-f]quinazoline 12, the 8H-pyrano[3,2-f]quinoxaline 13, and the 2H-pyrano[2,3-f]isoquinoline 15. The synthesis was achieved using conveniently substituted α,β-unsaturated aldehydes and organotitanium intermediates arising from azaheterocyclic phenols. Their photochromic behaviour (photocolouration yield, UV/VIS spectrum of photomerocyanines, rate constant of thermal bleaching) were studied besides those of corresponding naphthopyrans. The heterocycle effect and the role of substituents in the pyran moiety were investigated quantitatively through the study of the photochromic properties and the solvent effects. Diaryl-substituted azino-fused chromenes, especially isoquinoline derivatives, exhibit increased colourabilities and bathochromically shifted spectra for photomerocyanines which open up new prospects for photochromic applications.