The photochromism of [
Recently, many profitable applications
of photochromic dyes,
particularly spirooxazines, either as passive or active
devices, have been proposed [
In some cases, it has been reported that
thermal equilibrium between the closed (colorless form) and opened form
(colored merocyanine quinonoid form) is affected by the change in solvent
polarity [
The metal chlorides (Sigma-Aldrich, 99.99%)
were used as received. The synthesis of [
UV-visible absorption spectra were recorded on a range (200–650 nm) using λ-Helios SP Pye-Unicam spectrophotometer and/or Ocean Optics US4000 fiber optics spectrophotometer. Continuous irradiation experiments were performed using a 150 W xenon arc lamp (PTI-LPS-220 Photon Technology International, USA) operated at 70 W. Photochemical reactions were carried out in the spectrophotometric quartz cell with a homogeneously spread light on the cell window to avoid stirring. Measurements were made on aerated solutions.
Fluorescence spectra were measured in the range (290–750 nm) using Shimadzu RF5301 (PC) spectrofluorophotometer.
The
ring-closure reaction after photocoloration was monitored directly after
removal of light at room temperature. First-order rate constants were obtained
from the linear ln
The absorption spectrum of SP(I) and
SP(II) displayed two bands at 276 and 370 nm,
Table
The experimental values of absorption
maxima of SP and its open form (λSP, λopen), SP ring
opening rate constant
Compound | λSP(nm) | λopen(nm) | τopen-SP (min) | Colorability M−1cm−1 | |||
---|---|---|---|---|---|---|---|
SP(I) | 276 | 409 | 3.16 | 192 | 316 | 60 | 7.36 |
370 | |||||||
SP(II) | 276 | 404 | 7.96 | 529 | 125 | 66 | 1.30 |
370 |
Upon
irradiation of 60
The experimental values of
absorption, M(III)-SP formation rate constant
Complexes | λopen-M(III) (nm) | τM(III)-open-SP (min) | Colorability M−1cm−110−2 | |||
---|---|---|---|---|---|---|
Tb(III)-SP(I) | 412 | 4.04 | 661 | 247 | 163 | 7.02 |
Sm(III)-SP(I) | 414 | 4.55 | 258 | 219 | 56 | 7.85 |
Tb(III)-SP(II) | 412 | 8.16 | 327 | 122 | 40 | 7.73 |
Sm(III)-SP(II) | 414 | 4.77 | 225 | 209 | 47 | 7.72 |
UV/vis absorption spectra of SP(I) and its complexes with Tb3+ and Sm3+ ions in DMF before and after light irradiation ([SP(I)] =
[Ln3+] = 60
Effect of time of irradiation on the UV/vis absorption spectra of DMF solution
of a mixture of 60
Illustration of the reversible structural transformation of SP to the MC form in response to light in the absence and presence of Ln3+ metal ion.
Color development rate constant
Benzyl group substituent in SP(II) relative to the
smaller methyl group substituent in SP(I) accelerates both rates of
photocoloration and
thermal bleaching as reflected in the higher values of the
rate constants for SP(II) shown in Table
The ligand-centered luminescence was not observed in Tb3+ and Sm3+
complexes, whereas the typical characteristic narrow
emission bands of the Tb3+ (5D4
The sensitized luminescence spectra of 60
The substituent nature and the presence of lanthanide metal ions in solution of recently synthesized photochromic spirobenzopyrans of benzoxazine series induced significant changes in its photochromic parameters. It could be generally concluded that the presence of lanthanide ions significantly enhances the rate constants of both color development of the light-induced formation of the open merocyanine-like quinonoid species and the rate constant of its thermal bleaching. In most cases, colorability is enhanced. Moreover, strong characteristic sensitized luminescence of the lanthanide ions was observed due to efficient population of its emissive states via energy transfer from the open forms of the spirobenzoxazines.
Russian Foundation for Basic Research supported the Russian team (Grant 07-03-234).