Preventing the Formation of the Long-Lived Colored Transoid-Trans Photoisomer in Photochromic Benzopyrans

Abstract

A new photochromic fused benzopyran presenting a bridge between the pyran double bond and the benzenic ring was prepared. While the UV irradiation of usual benzopyrans leads to the formation of two colored photoisomers with very different thermal stabilities, studies by laser flash photolysis showed that the presence of this particular bridge prevents the formation of the undesirable long-lived colored TT isomer and therefore after laser irradiation the colored solution fades following a fast monoexponential decay.

Fast T-Type Photochromism of Colloidal Cu-Doped ZnS Nanocrystals

“…Among these, fast thermally reversible (T-type) photochromic compounds, whose time scales of the thermal back reactions are sub-microseconds to seconds (e.g. bridged-imidazole dimers, [5][6][7][8][9][10] oxazines, [11][12][13] and naphthopyran derivatives [14][15][16][17][18] ), are especially promising for ophthalmic lenses, fluorescence switches for bioimaging, 19,20 and holographic 3D displays. [21][22][23] These materials can tune colors and colorfading speeds from tens of nanoseconds to tens of seconds.…”

Extending the Lifetimes of Charge Transfer States Generated by Photoinduced Heterolysis of Photochromic Radical Complexes

“…Among them, fast thermally reversible (T‐type) photochromic molecules, whose photogenerated colored species quickly and automatically reverts to the initial species by heat, have been paid particular attention because these fast photoswitching properties are promising for various industrial applications, such as ophthalmic lenses, [5] dynamic holographic materials, [6,7] fluorescent switching dyes for bioimaging [8–10] . Therefore, a number of fast photochromic compounds have been reported so far such as bridged imidazole dimers, [11–15] naphthopyrans, [16–20] oxazines, [21,22] and diarylethene derivatives [23,24] …”

Highly transparent photochromic films with a tunable and fast solution-like response

“…The first approach consists in the synthesis of new photochromic molecules with minimal conformational changes along the photochromic interconversion to minimize the matrix effect. This has been mainly achieved with imidazole-based molecules, [21][22][23][24][25][26][27][28][29][30][31][32][33] prepared by Abe et al, or preventing the formation of the naphthopyrans (transoid-trans) [34][35][36][37][38][39][40][41][42][43] /spirooxazines (trans-merocyanines) 44,45 long-lived isomeric open form, responsible for the slowdown of the ring-closure reaction (oxazines, substituted…”