“…2 In order to improve the colorability, photostability and fatigue resistance performances of benzopyrans, numerous investigations have been carried out by means of modulating the kinetic equilibrium towards TC or TT isomers based on inductive, mesomeric and steric effects, heterocyclic substitution and ring annulation strategies. [6][7][8][9][10][11][12][13][14][15][16][17][18][19] Fully T-type photochromism chromenes have been synthesized with suitable substitutions toward a pyran ring that stabilizes the TC isomer, and thus prevents the ensuing formation of TT both thermally and optically [8][9][10] and guarantees promising applications in photochromic lenses. On the other hand, helicene annulation gives rise to P-type chromenes 6,7 with potential applications, such as molecular motors, high density data storage devices and electronic devices.…”