Highly stable and fluorescent switching spirooxazines

Photoswitchable Photochromic Chelating Spironaphthoxazines: Synthesis, Photophysical Properties, Quantum-Chemical Calculations, and Complexation Ability

The stable and efficient photochromic and photoswitchable molecular systems designed from spirooxazines are of increasing scientific and practical interest because of their present and future applications in advanced technologies. Among these compounds, chelating spironaphthoxazines have received widespread attention due to their efficient optical response after complexation with some metal ions being of biomedical interest and environmental importance, as well as their good cycle performance and high reliability, especially by metal ion sensing. In this mini-review, we summarize our results in the design of novel photoswitchable chelating spironaphthoxazines with specific substituents in their naphthoxazine or indoline ring systems in view of recent progress in the development of such molecular systems and their applications as metal ion sensors. The design, synthesis methods, and photoresponse of such spirooxazine derivatives relevant to their applications, as well as quantum-chemical calculations for these compounds, are presented. Examples of various design concepts are discussed, such as sulfobutyl, hydroxyl, benzothiazolyl, or ester and carboxylic acid as substituents in the chelating spironaphthoxazine molecules. Further developments and improvements of this interesting and promising kind of molecular photoswitches are outlined.

A Photochromic Sensor Microchip for High-Performance Multiplex Metal Ion Detection

Photochromic molecules can respond to external stimulations and undergo reversible conversion between different chemical structures, providing one photochromic molecule with multiple recognition states for targeting compounds. Here we design a facile sensor microchip with only one photochromic molecule (spirooxazine) to discriminate multiplex metal ions. The sensor chip performs in dark, ultraviolet, or visual stimulation, resulting in different molecular states of spirooxazine-metallic coordination and patterned fluorescent signals for analysis. By using this sensor microchip, 11 metal ions are discriminated. Furthermore, mineral water of 16 different brands and metal ions in human serum are distinguished.

Synthesis and photochromism of naphthopyrans bearing naphthalimide chromophore: predominant thermal reversibility in color-fading and fluorescence switch

Two novel photochromic naphthopyrans containing naphthalimide moieties (Nip1 and Nip2) were studied in solution under flash photolysis conditions, exhibiting highly photochromic response, rapid thermal bleaching rate and good fatigue-resistance. Owing to the different N-substituted imide groups at the naphthalimide units, the thermal bleaching rate of Nip2 bearing phenyl on the naphthalimide unit is found to be approximately 2 times that of Nip1 bearing n-butyl, indicating that the photochromic properties can be modulated with introduction of different functional groups on the naphthalimide unit. In Nip1 and Nip2, the strong electron-withdrawing effect of the imide group incorporated at the naphthalimide moiety maintains several merits: (i) shifting absorption bands to longer wavelength, (ii) beneficial to an enhancement in the ratio of transoid-cis (TC) isomer and an increase in the transformation rate from transoid-trans (TT) to TC with respect to reference compound NP, and (iii) resulting in a preferable color bleaching rate and fading absolutely to their colorless state with thermal reversibility. As demonstrated in the system of NP, the slow transformation process from TT to TC might be the predominant dynamic step in thermal back process, leading to the residual color of NP being only faded to its original colorless state by visible light irradiation. The optical densities of colored forms for Nip1 and Nip2 are dependent upon the intensity of incident light, ensuring a possible application in the manufacture of ophthalmic lenses and smart windows. Moreover, the fluorescence of Nip1 and Nip2 can be switched on and off by photoinduced conversion between the closed and open forms.