Photochromism - Revision history

Cmditradmin: /* Isosbestic Point */

2010-08-10T20:30:01Z

Isosbestic Point

← Older revision		Revision as of 13:30, 10 August 2010
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	:<math>A(\lambda)= N_A \epsilon_A^{\lambda} + N_B\epsilon_B^{\lambda}\,\!</math>		:<math>A(\lambda)= N_A \epsilon_A^{\lambda} + N_B\epsilon_B^{\lambda}\,\!</math>
	[[Image:~~Isosbestic~~.png\|thumb\|300px\|Absorption curves for several species of chemicals cross at the isobestic point.]]		[[Image:Bromocresol green spectrum.png\|thumb\|300px\|Absorption curves for several species of chemicals cross at the isobestic point.]]

	If at one wavelength the extinction coefficients are equal they can be factored out:		If at one wavelength the extinction coefficients are equal they can be factored out:

Cmditradmin: /* Photochromism */

2010-08-10T18:31:10Z

Photochromism

← Older revision		Revision as of 11:31, 10 August 2010
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	See also Photochromism, Molecules, and Systems by Dürr<ref>Photochromism, Molecules, and Systems ,H. Dürr and H. Bouas-Laurent (Eds.)(Studies in Organic Chemistry 40), Elsevier, Amsterdam, 1990(1068 pp.).</ref>		See also Photochromism, Molecules, and Systems by Dürr<ref>Photochromism, Molecules, and Systems ,H. Dürr and H. Bouas-Laurent (Eds.)(Studies in Organic Chemistry 40), Elsevier, Amsterdam, 1990(1068 pp.).</ref>

	See ~~also Wikipedia on~~ [~~http~~:~~//en.wikipedia.org/wiki/Photochromism~~ Photochromism]		See [[wikipedia:Photochromism]]

	=== Interconversion of Isomers ===		=== Interconversion of Isomers ===

Cmditradmin: /* References */

2010-06-23T16:53:35Z

References

← Older revision		Revision as of 09:53, 23 June 2010
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	<br clear='all'>		<br clear='all'>
	[[category:absorption]]		[[category:absorption]][[category:photochromism]]
	<table id="toc" style="width: 100%">		<table id="toc" style="width: 100%">
	<tr>		<tr>

Cmditradmin at 20:05, 29 December 2009

2009-12-29T20:05:31Z

← Older revision		Revision as of 13:05, 29 December 2009
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	<br clear='all'>		<br clear='all'>
			[[category:absorption]]
	<table id="toc" style="width: 100%">		<table id="toc" style="width: 100%">
	<tr>		<tr>

Cmditradmin: /* Heterocyclic Cleavage */

2009-09-15T21:22:47Z

Heterocyclic Cleavage

← Older revision		Revision as of 14:22, 15 September 2009
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	*fast thermal back reaction		*fast thermal back reaction

	These molecules are used for various photochromic reactions but they break down after 10 ^5 repetitions. Their change in optical properties are dramatic and can be used for low repetition application such as real time holography in which an image is written but only needs to be changed a few times.		These molecules are used for various photochromic reactions but they break down after 10<sup>5</sup> repetitions. Their change in optical properties are dramatic and can be used for low repetition application such as real time holography in which an image is written but only needs to be changed a few times.

	== References ==		== References ==

Cmditradmin: /* Isosbestic Point */

2009-09-15T21:21:27Z

Isosbestic Point

← Older revision		Revision as of 14:21, 15 September 2009
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	:<math>A(\lambda)= N_A \epsilon_A^{\lambda} + N_B\epsilon_B^{\lambda}\,\!</math>		:<math>A(\lambda)= N_A \epsilon_A^{\lambda} + N_B\epsilon_B^{\lambda}\,\!</math>
	[[Image:Isosbestic.png\|thumb\|300px\|]]		[[Image:Isosbestic.png\|thumb\|300px\|Absorption curves for several species of chemicals cross at the isobestic point.]]

	If at one wavelength the extinction coefficients are equal they can be factored out:		If at one wavelength the extinction coefficients are equal they can be factored out:

Cmditradmin at 21:15, 15 September 2009

2009-09-15T21:15:27Z

← Older revision		Revision as of 14:15, 15 September 2009
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	:<math>k_{bl}\,\!</math> rate of photobleaching		:<math>k_{bl}\,\!</math> rate of photobleaching

	=== Example Photochromic Reaction ===		==== Example Photochromic Reaction ====
	[[Image:Spiropyran.png\|thumb\|300px\|Spiropyran photochromic reaction]]		[[Image:Spiropyran.png\|thumb\|300px\|Spiropyran photochromic reaction]]
	An example of a photochromic reaction involving a spiropyran which is a merocyanin. This is a conjugated molecule. On the B form the O<sup>-</sup> is donor and the C double bond N<sup>+</sup> is an acceptor. This leads to a charge transfer absorption band that makes the molecule purple. Whereas the A form has a benzene ring with a nitrogen that absorbs in the UV. The oxygen transfers charge to the nitrogen and this probably makes the molecule somewhat yellow. Ideally the quantum yield for φ 1 (A going to B) is equal to the quantum yield for φ 2 (B going to A) and equal to 1. Thus every time you put in photon in it goes back and forth, and you control which way it goes by the wavelength of the photon.		An example of a photochromic reaction involving a spiropyran which is a merocyanin. This is a conjugated molecule. On the B form the O<sup>-</sup> is donor and the C double bond N<sup>+</sup> is an acceptor. This leads to a charge transfer absorption band that makes the molecule purple. Whereas the A form has a benzene ring with a nitrogen that absorbs in the UV. The oxygen transfers charge to the nitrogen and this probably makes the molecule somewhat yellow. Ideally the quantum yield for φ 1 (A going to B) is equal to the quantum yield for φ 2 (B going to A) and equal to 1. Thus every time you put in photon in it goes back and forth, and you control which way it goes by the wavelength of the photon.
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	:<math>\Phi_3\,\!</math> is the decomposition quantum yield		:<math>\Phi_3\,\!</math> is the decomposition quantum yield

	=== Photochemical Degradation ===		==== Photochemical Degradation ====

	However, if the quantum yield for degradation (i.e., formation of C) is f3, the non-degraded fraction y after n cycles will be:		However, if the quantum yield for degradation (i.e., formation of C) is f3, the non-degraded fraction y after n cycles will be:

Cmditradmin: /* Photochemical Reaction Fatigue */

2009-09-15T21:14:05Z

Photochemical Reaction Fatigue

← Older revision		Revision as of 14:14, 15 September 2009
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	=== Photochemical Reaction Fatigue ===		=== Photochemical Reaction Fatigue ===
	Photochemical fatigue is gradual exhaustion of a photochromic system with repeated cycling so it ~~is become~~ locked in a certain state.		Photochemical fatigue is gradual exhaustion of a photochromic system with repeated cycling so it becomes locked in a certain state.

	Photochemical fatigue has for many years limited the use of photochromic materials for optical memory. Even today rewriteable discs do not use photochromic materials, instead they utilize phase change going from one crystalline form to another that results in different reflectivity. A magnetic memory is written over hundreds of thousand of times, this is the requirement. For a photochemical to be useful it must have a very low quantum yield for any decomposition pathway. The quantum yield is independent of light intensity.		Photochemical fatigue has for many years limited the use of photochromic materials for optical memory. Even today rewriteable discs do not use photochromic materials, instead they utilize phase change going from one crystalline form to another that results in different reflectivity. A magnetic memory is written over hundreds of thousand of times, this is the requirement. For a photochemical to be useful it must have a very low quantum yield for any decomposition pathway. The quantum yield is independent of light intensity.

Cmditradmin: /* Photochemical Reaction Fatigue */

2009-09-15T21:13:47Z

Photochemical Reaction Fatigue

← Older revision		Revision as of 14:13, 15 September 2009
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	=== Photochemical Reaction Fatigue ===		=== Photochemical Reaction Fatigue ===
			Photochemical fatigue is gradual exhaustion of a photochromic system with repeated cycling so it is become locked in a certain state.

	Photochemical fatigue has for many years limited the use of photochromic materials for optical memory. Even today rewriteable discs do not use photochromic materials, instead they utilize phase change going from one crystalline form to another that results in different reflectivity. A magnetic memory is written over hundreds of thousand of times, this is the requirement. For a photochemical to be useful it must have a very low quantum yield for any decomposition pathway. The quantum yield is independent of light intensity.		Photochemical fatigue has for many years limited the use of photochromic materials for optical memory. Even today rewriteable discs do not use photochromic materials, instead they utilize phase change going from one crystalline form to another that results in different reflectivity. A magnetic memory is written over hundreds of thousand of times, this is the requirement. For a photochemical to be useful it must have a very low quantum yield for any decomposition pathway. The quantum yield is independent of light intensity.

Cmditradmin: /* Isosbestic Point */

2009-09-15T21:11:44Z

Isosbestic Point

← Older revision		Revision as of 14:11, 15 September 2009
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	=== Isosbestic Point ===		=== Isosbestic Point ===
			The isobestic point is the wavelength at which a mixture of forms or species of a chemical have the same absorbance. It provides a some clues about the nature of the reactions occuring.

	Consider the absorption spectra of a composite comprised of A and B. The absorption at λ equals the number of molecules of A times the extinction coefficient of A at λ plus the number of molecules of B plus the extinction coefficient of B at λ.		Consider the absorption spectra of a composite comprised of A and B. The absorption at λ equals the number of molecules of A times the extinction coefficient of A at λ plus the number of molecules of B plus the extinction coefficient of B at λ.