Photochromic compounds based on ring opening and closing of a {1,3}oxazine compound
We have designed a molecular switch based on the photoinduced opening and thermal closing of a [1,3]oxazine ring. A substituted [1,3]oxazine compound described as having a general (i.e., unsubstituted) structure with fused indoline and benzooxazine fragments such that they share a common bond in the [1,3]oxazine compound: (i) the bond connecting positions 1 and 2 of the indoline fragment and (ii) the bond connecting positions 2 and 3 of the benzooxazine fragment. Irradiation by light of suitable wavelength and intensity of this photochromic compound induces cleavage of a [C—O] bond of the [1,3]oxazine ring to form a phenolate chromophore. The photogenerated (e.g., colored) isomer may revert thermally to the starting (e.g., colorless) oxazine. Alternatively, the switch may be between isomers of the compound that absorb at different wavelengths. Reversible coloration of silica or polymeric materials and switching optical signals may involve many cycles of interconversion between different colored states. A colorless/colored state may be maintained by constant irradiation or chemical trapping.
1. A photochromic compound which is a [1,3]oxazine compound substituted at one or more positions, wherein the unsubstituted [1,3]oxazine compound is described as having a structure with fused indoline and benzooxazine fragments such that they are fused along (i) the bond connecting positions 1 and 2 of the indoline fragment and (ii) the bond connecting positions 2 and 3 of the benzooxazine fragment, and further substituted by an electron withdrawing group for a hydrogen attached at any position of the phenyl ring of the benzooxazine fragment, wherein said [1,3]oxazine compound has a substituted structure as shown in Formula I:
wherein R 1 , R 4 , and R 5 are selected to adjust (i) excitation wavelength for cleavage of the [C—O] bond in said compound to produce a phenolate derivative by the ring cleavage and (ii) absorbance wavelength of the phenolate derivative and R 2 and R 3 are selected to adjust the [1,3]oxazine compound's rate of coloration and/or decoloration,
wherein said R 2 and R 3 are different;
wherein said R 1 is selected from the group consisting of hydrogen, hydroxyl, C1-C4 alkyls, C5-C6 cycloalkyls, substituted C1-C4 alkyls, substituted C5-C6 cycloalkyls, C5-C6 aryls, substituted C5-C6 aryls, C5-C6 heterocycles, and substituted C5-C6 heterocycles;
wherein said R 2 is selected from the group consisting of hydrogen, hydroxyl, C1-C4 alkyls, C5-C6 cycloalkyls, substituted C1-C4 alkyls, substituted C5-C6 cycloalkyls, C5-C6 aryls, substituted C5-C6 aryls, C5-C6 heterocycles, and substituted C5-C6 heterocycles;
wherein said R 3 is selected from the group consisting of hydrogen, hydroxyl, C1-C4 alkyls, C5-C6 cycloalkyls, substituted C1-C4 alkyls, substituted C5-C6 cycloalkyls, C5-C6 aryls, substituted C5-C6 aryls, C5-C6 heterocycles, and substituted C5-C6 heterocycles;
wherein said R 4 is selected from the group consisting of hydrogen, hydroxyl, C1-C4 alkyls, C5-C6 cycloalkyls, substituted C1-C4 alkyls, substituted C5-C6 cycloalkyls, C5-C6 aryls, substituted C5-C6 aryls, C5-C6 heterocycles, and substituted C5-C6 heterocycles;
wherein said R 5 is a nitrogen-containing group or any other electron withdrawing substituent;
wherein a light excitation induces cleavage of a [C—O] bond in the oxazine ring of said compound to produce a phenolate derivative by ring cleavage;
wherein said compound switches to said phenolate derivative in 250 ns or less;
wherein isomerization between said compound and said phenolate derivative is thermally reversible without said light.
2. The compound of claim 1 , wherein light induces cleavage of a [C—O] bond in the oxazine ring of said compound to produce a phenolate derivative by ring cleavage, wherein said light has a wavelength from 200 nm to 800 nm.
3. The compound of claim 1 , wherein light induces cleavage of a [C—O] bond in the oxazine ring of said compound to produce a phenolate derivative by ring cleavage, wherein said light has a wavelength from 800 nm to 1300 nm.
4. A method of making the compound of claim 1 , said method comprising N-alkylating 2-R 4 -3,3′-R 2 ,R 3 -6—R 1 -3H-indole with 2-chloromethyl-4-R 5 -phenol to produce an intermediate and then cyclizing the intermediate under basic conditions.
5. The photochromic compound of claim 1 wherein said compound remain able to isomerizes between said compound and said phenolate derivative over greater than 1000 excitation cycles.