Abstract
The photochromism of [7′-hydroxy-8′-formyl-3-methyl-4-oxospiro[1,3-benzoxazin-2,2′-[2H-1]benzopyran],SP(I),[7′-hydroxy-8′-formyl-3-benzyl-4-oxospiro[1,3-benzoxazin-2,2′-[2H-1]benzopyran] SP(II) and their coordination with Tb3+and Sm3+ ions have been studied in DMF. UV/vis induced-color development due to heterolytic bond cleavage of SP(I) and SP(II) is greatly influenced by complexation with the lanthanide ions. The irradiation-induced color enhancement due to ring opening and thermal decoloration of the open forms of SP(I), SP(II) follows first-order kinetics. Physical characteristics of the studied systems such as colorability and relaxation time of thermal bleaching parameters were determined. Moreover, light-energy transfer-induced luminescence of lanthanide ions via coordination with the two spirobenzoxazines was monitored.
Highlights
It has been reported that thermal equilibrium between the closed and opened form is affected by the change in solvent polarity [14, 15], since polar solvents promote the formation of the colored form at room temperature in the absence of light
We report on the possibility to stabilize the colored open forms of the recently synthesized spirobenzoxazines SP(I) and SP(II) toward thermal bleaching by coordination with Tb3+ and Sm3+ ions in polar DMF solvent
First-order kinetics rate constants of the reversible close open reactions were determined graphically (Figure 2, as an example) and data are collected in Tables 1 and 2
Summary
Many profitable applications of photochromic dyes, spirooxazines, either as passive or active devices, have been proposed [1,2,3,4,5,6,7,8,9,10,11,12,13]. 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 [14, 15], since polar solvents promote the formation of the colored form at room temperature in the absence of light. The equilibrium between both forms is strongly displaced upon irradiation to the side of open-chain colored photomerocyanine and spontaneously converts to the colorless spiro form to reach thermal equilibrium immediately after removing the light [15]. The expected light-energy transfer-induced characteristic luminescence of lanthanide ions via complexation with the merocyanine quinonoid open forms of the two spirobenzoxazines will be explored
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