On‐Demand Control of the Photochromic Properties of Naphthopyrans

Abstract

minutes/hours to completely return to the CF. The residual color imparted by the TT form and the slow thermal back-reaction of the TC form are considered as problems to be solved. [9][10][11][12][13] The thermal backreaction speed of colored naphthopyrans can be modulated by the introduction of an electron-donating group at the para position of the 3-phenyl ring. [4] However, substitution at the 3-phenyl ring typically causes significant changes in the color of the colored species. Although the speed of the thermal back-reaction can be modulated by exploiting steric effects to destabilize the TC form and the long-lived TT form, the synthetic procedures required to yield the desired products are not simple and moderate control of the thermal backreaction speed for photochromic lenses is difficult to achieve. [14][15][16][17][18][19] In order to design appropriate naphthopyran derivatives showing on-demand photochromic properties, the independent control of the thermal back-reaction speed is an important challenge in the development of advanced photochromic materials. Within this context, we herein present a molecular design strategy that can be used to modulate the thermal fading speed without significant changes to other photochromic properties.In this study, we designed novel naphthopyran derivatives possessing alkylenedioxy moieties as a means to control the thermal fading speed of the TC form and reduce the generation of the long-lived TT form. The reactivity and optical properties of the 1,2-alkylenedioxy benzene significantly depend on the ring-size of the alkylenedioxy moiety owing to changes in electron-donating ability and π-conjugation length upon changing the conformation of the ring. [20][21][22] We introduced alkylenedioxy moieties to the 9-and 10-positions of 3H-naphthopyran (3HNP) and investigated the effects of ring size on the photochromic properties of the resultant molecules. Remarkably, the thermal back-reaction speed of the newly designed naphthopyran derivatives was found to be controllable independently of other photochromic properties, such as the color of the colored species, by changing the alkyl chain length of the alkylenedioxy moiety. In addition, intramolecular hydrogen bonding is very important for modulating the conformation and stability of the structural isomers. [23,24] The undesirable residual color attributable to the formation of the TT form upon cessation of light irradiation is effectively reduced owing to the hydrogen bonding between the oxygen atom at the 10-position and the olefinic proton at the 1-position in the TC form, resulting in fast photoswitchable Photofunctional compounds have emerged as critically important materials for both fundamental studies and industrial applications. Control of the thermal decoloration speed to within several seconds while sustaining satisfactory photochromic colorability is an important challenge for the application of such materials to photochromic lenses and smart windows. Photochromic naphthopyran derivatives are utilized for photoch...

On-demand regulation of photochromic behavior through various counterions for high-level security printing

“…In particular, the abil ity to tune the coloration rate on demand can significantly improve the security level of the recorded texts, because different informa tion would appear using various irradiation times. To date, progress has been made in the regulation of colorability and coloration rates by incorporation of electron donor or acceptor substitutions in photo chromic molecules (17,18). Nevertheless, the prepared photochromic materials generally have constant colorability and coloration rates under the same light irradiation condition (19)(20)(21)(22)(23)(24)(25).…”

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

“…[1][2][3][4] 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][9][10] Therefore, a number of fast photochromic compounds have been reported so far such as bridged imidazole dimers, [11][12][13][14][15] naphthopyrans, [16][17][18][19][20] oxazines, [21,22] and diarylethene derivatives. [23,24] Phenoxyl-imidazolyl radical complex (PIC) is one of the recently developed rate-tunable T-type photochromic compounds which reversibly generates an imidazolyl radical and a phenoxyl radical (ring-opening form) in a molecule by UV light irradiation (Scheme 1a).…”

Self‐Regulating Contact Lenses with the Patterning of a Photochromic Layer Based on Wettability Contrast

“…The SP is isomerized to the merocyanine (MC) upon the illumination of UV light, in which the sp 2 hybridization and π–π: transition lead to the light absorption. [ 28,29 ] The thermal reversion from MC to SP occurs at room temperature or at the exposure of visible light, which is suitable for the use of ordinary circumstances. To achieve the capability of broadband light regulation, we used SP dyes D 1 , D 2 , and D 3 that have different central wavelengths of the absorption peak at 550, 430, and 570 nm, respectively.…”