Investigation of the Photochromic Effect of Spiro [indolino-naphthoxazine] Derivatives by Time-Resolved Spectroscopy

Abstract

Based on the results of different spectroscopic techniques, a reaction scheme is proposed to explain the photochromism of indolinospironaphthoxazine derivatives. Pump-probe experiments with picosecond time-resolution show that bond breakage in the excited spiro form occurs within less than 2 ps. The primary photoproduct, a non-planar intermediate X*, decays into a mixture of isomers, usually termed "photomerocyanines". The lifetime of the intermediate X*, which varies between 3 and 11 ps, depends both on nature of the solvent and kind of substituent.A fluorescence emission exhibiting a large Stokes shift and a non-exponential decay (tl/c at 1 ns) is attributed to a solvent stabilized intermediate X*', which does not contribute significantly to the formation of the "photomerocyanine" forms. The excited state lifetimes of the dominant merocyanine isomers were determined to be around 10 ps and 800 ps, resp., depending on solvent and substituent.Spontaneous resonance Raman and time-resolved CARS spectroscopy prove the existence of at least two isomeric species in the room-temperature photolyzed solutions. The similarity in vibrational frequencies suggests that corresponding isomeric forms occurring in polar and unpolar solvents, resp., are similar in structure; they differ, however, in Franck-Condon factors for excitation So -Si. The thermodynamic equilibrium distribution of the isomeric "photomerocyanine" species is reached on the time scale of the decay of the intermediate X*.In dieser Arbeit wird zusammenfassend iiber die Ergebnisse von Untersuchungen zur Photochromie von Spironaphthoxazinen berichtet und ein Reaktionsschema vorgeschlagen. Pump-Abfrage-Experimente mit Pikosekunden-Zeitauflosung belegen, daB die Bindung zwischen dem Sauerstoff und dem Spirokohlenstoff in weniger als 2xl0"12s Brought to you by | Universita degli Studi di Padova Authenticated Download Date | 3/29/16 4:11 AM 92 S. Schneider nach der elektronischen Anregung gebrochen wird. Das nicht-planare Zwischenprodukt entsteht in einem angeregten Zustand X*, der je nach Losungsmittel in (3 bis 11) x 10"12 s in ein Isomerengemisch von annahernd planaren, merocyaninartigen Strukturen ubergeht. Nach UV-Anregung der Spiroform wird eine nicht-exponentiell abklingende Emission mit starker Stokes-Verschiebung registriert. Als Ursprung werden besonders solvatisierte Intermediate X*' diskutiert, die nicht effizient in die "Photomerocyanin"-Form zerfallen.Die zeitaufgelosten Resonanz-Raman-und CARS-Spektren belegen die Existenz von mindestens zwei verschiedenen, merocyaninartigen Isomeren in alien Losungsmitteln. Aufgrund der Ahnlichkeit der beobachteten Schwingungsfrequenzen wird geschlossen, daB in polaren und unpolaren Losungsmitteln strukturell sehr ahnliche Isomere vorliegen. Das Isomerenverhaltnis, das der thermodynamischen Gleichgewichtsverteilung entspricht, wird nach UV-Belichtung innerhalb der Zerfallszeit des Intermediaten X* erreicht.Brought to you by | Universita degli Studi di Padova Authenticated Download Date | 3/29/16 4:11 AM

Advances in Spiropyrans/Spirooxazines and Applications Based on Fluorescence Resonance Energy Transfer (FRET) with Fluorescent Materials

“…In-depth basic research on the photophysics and photochemical processes of spirooxazines has been carried out. Schneider et al studied the mechanism of photochromism of spirooxazines by picosecond time-resolved absorption spectra, as well as time-resolved spontaneous and coherent anti-stokes Raman scattering [ 40 ]. Kellmann and colleagues studied the light physics and dynamics of spirooxazines in 1989 [ 41 ].…”

Substituent and solvent effect on the photochromic properties of a series of spiroindolinonaphthooxazines

“…It has attracted much attention because of the wide variety of practical applications of photochromic systems most of which are spiro-compounds (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18). Among them, the compounds of the spiroindolinonaphthooxazine series (SO) are a topic of increasing interest because of their good colouring power and photofatigue resistance both providing a potential application in many new technologies such as data recording and storage, optical switching, displays and nonlinear optics (3-18).…”

A Photochromic Copolymer Hydrogel Contact Lens: From Synthesis to Application

“…The absorption spectrums were broad in both hydrogels; this was mainly related to the coloring mechanism. After UV illumination, bond breakage in the excited spiro form on SPO occurred; the intermediate X was produced first, which then decayed into zwitterionic merocyanines, because the merocyanines were mixture of at least four isomers and their optical spectrums were broad absorption bands [32]. We observed that UV irradiation of the hydrogel made by immersing method at 365 nm led to the maximum absorbance ( max ) at 620 nm (Figure 4(a)), while in the hydrogel made by polymerization method there was a shift in max to a shorter wavelength, which was 610 nm (Figure 4(b)).…”