Rapid decoloration and acidichromism of photochromic 3,3-diaryl-3H-pyrano[3,2-f]quinolines

• Published in: Tetrahedron 2019-09, Vol.75 (38), p.130471, Article 130471
• Main Authors: Li, Bin, Sun, Zipei, Zhai, Yan, Jiang, Jianlan, Huang, Yaodong, Meng, Jiben
• Format: Article
• Language: English
• Subjects: Acidichromism; Bathochromic shift; Fading speed; Photochromism; Pyranoquinolines
• ISSN: 0040-4020; 1464-5416
• DOI: 10.1016/j.tet.2019.130471

Pyranoquinoline, with its light-sensitive fragment and coordination node, provides an ideal matrix for the development of multi-functional photochromic compounds. This paper presents the synthesis and photochromic properties of 3,3-diaryl-3H-pyrano[3,2-f]quinoline derivatives QP1-QP8. All exhibited good photochromism under UV light irradiation followed by biexponential kinetic decay in the dark at ambient temperature. Their photochromic processes were reversible, and acidichromism was observed to occur in solution. The fading speeds of QP2 and QP6 were higher than those of their known naphthopyran counterparts, whereas the decoloring speeds of the six other compounds were all over an order of magnitude higher than those of QP2 and QP6. The synthesized pyranoquinolines exhibited very good fatigue resistance both in solution and the solid state. Compared to other pyranoquinolines, the optical densities of QP2 and QP6, i.e., the compounds with 2,4-dimethoxylphenyl and 1-naphthyl, were enhanced dramatically. For all the synthesized pyranoquinolines, a distinct bathochromic shift was observed with increasing solvent polarity. The structure-property relationship of the pyranoquinolines was revealed through the single-crystal X-ray analysis of QP1 and QP7. [Display omitted] •The photochromic and acidichromism properties of pyranoquinoline derivatives were investigated.•All the synthesized compounds exhibited reversible photochromic processes.•All the solutions of N-protonated compounds did not undergo ring-opening processes under UV irradiation.