Use Photochromic Materials Technology Coloring World

Home > Color Shifting Technologies > Photochromic

Photochromic Materials Examples

Art-and-Crafts

UV-Dosimetry

Educational-Materials

Eyewear

Fashion-and-Accessories

Health-and-Safety-Equipment

Medical-Devices

Nail-Art

Novelty-Items

Promotional-Items

Protective-Gear

Security-Printing

Photochromic Pigment Materials

black cb-11

blue cb-09

brown cb-05

coffee cc-10

dark purple cdp-04

green cg-07

sky blue csb-08

violet cv-12

yellow cy-14

red cr-01

grey cg-06

orange co-13

orange-red cor-03

pink cp-02

purple cp-15

red kb-01

brown kb-04

black kb-06

coffee kc-03

dark purple kdr-07

blue ub-13

dark red udr-14

gree ug-04

grey ug-10

dark purple cdp-04

orange uo-18

purple up-19

yellow uy-01

viulet uv-12

sky-blue usb-17

yellow-red uvyr-10

yellow-green uvyg-17

red-purple uvrp-19

purple-orange uvpo-11

pink-purple uvpp-14

orange-purple uvop-16

magenta-purple uvmp-12

grey-purple uvgp-13

green-coffee uvgc-01

green-blue uvgb-18

It has been more than 100 years since the discovery of the organic photochromism. The genuine emergency of organic photochromism can date back to 1980s when people discovered the compounds such as benzopyrans and spirooxazines that have better fatigue-resistance function. Currently, the research of photochromic compounds mainly concentrates on related heterocyclic compounds such as spirooxazines, spiropyrans, diarylethenes, captodative acid anhydrides.

How photochromic materials work?

It refers to that a compound (A) produces a product (B) when undergoing a specific photochemical reaction. That process happens under the condition the A is exposed to light of a certain wavelength. During this process, there is a noticeable change in A’s absorption spectrum as there is a change in electronic configuration and structure. However, when being exposed to thermal means and another different wavelength of light, the A can go back to its original form.

Types of Organic Photochromic Compounds

There are many types of organic photochromic materials with different reaction mechanism.

①Cycloaddition reactions, covering diarylethenes and captodative acid anhydrides;

②Oxidation-reduction reactions, covering thiazines and polycyclic aromatic compounds;

③Cis-trans isomerization, covering azo compounds and naphthopyran dyes;

④Electron transfer tautomerization, covering salicylidene aniline derivatives;

⑤Homolytic bond cleavage, covering hexaphenylbiimidazoles;

⑥Heterolytic bond cleavage, covering spirooxazines and spiropyrans.

Here are some organic photochromic compounds.

1 Spiropyran

Spiropyran is a kind of organic photochromic compounds that has been most extensively studied and been researched the earliest.

The color-changing of spiropyrans is to generate open-ring compounds with conjugated structures. During this process, an intramolecular cycloreversion reaction will generate via heterolytic bond cleavage.

The color change reaction is:

For spiropyrans, the maximum absorption wavelength of the open-ring form generally being less than 600 nm. It is easy to be oxidized and degraded with poor fatigue resistance. It has sound photochromic properties. There are several methods for synthesizing spiropyran compounds. The yields rate can be over 90%.

2 Spirooxazine

Spirooxazine is a kind of compounds with sound photochromic performance. It was developed on ther basis of spiropyran in 1970s.

It is most promising for entering the field of photochromic materials, as it has good fatigue-resistance, stable chemical property and fast response. Its color-changing is similar to that of spiropyran, which can be explained as follows:

It is a kind of organic photochromic compounds with strong light stability and fatigue-resistance.

Recently, there are several spirooxazine compounds that are produced by Chung2Chun Lee et al. using microwave synthesis.

The yield rate of this method is not high, only around 40%. But it can, in tens of minutes, generate yields that equals to what traditional method will take several hours to generate. Compared to traditional method, it has greatly improved efficiency.

3 Chromene

Chromenes has good photostability, decolorization rates, sound light responsiveness. It is a kind of benzopyran compounds with extensive research. The color-changing reaction is as follows:

4 Fulgide

Fulgides can generate photochromic phenomena by undergoing valence tautomerism to trigger intramolecular cycloreversions. It refers collectively to substituted dialky lidenemalonate anhydrides. The color-changing is as follows:

Fulgide is a good optical data storage material that is erasable. It can be rewritten over ten thousand times. It has good fatigue resistance, long storage life, good thermal and photo stability. We observe that in some phenyl-substituted fulgides in crystalline states, solutions, glasses, and polymers, there is photochromism. There are also some pronounced solvatochromic effects. Currently, furan-substituted fulgide is the most deeply and extensively researched.

5 Azo Compounds

The photochromism of azo compounds is generated through a cis-trans isomerization reaction of the bond. The color-changing is as follows:

It is very important to study and design new azo compounds. Azo compounds has non-destructive readout of information and ultra-high storage density. This is its advantage. It is a new type of information storage material. It also has disadvantage, that is, their thermal stability is poor and there is a small change in the absorption spectrum before and after color change.

6 Diarylethene

Diarylethenes can also generate a reversible cycloreversion as well as a cis-trans isomerization reaction. The dihydro phenanthrene generated by the cyclization is easy to regenerate phenanthrene due to oxidation and dehydrogenation. Diarylethenes are a kind of photochromic compounds that were discovered relatively early. This compound is generated based on cis-trans isomerization. The color-changing is as follows:

Diarylethenes have received much attention from researchers. It has some advantages that other photochromic compounds, such as spirooxazines, spiropyranes, azobenzenes, don’t possess. It has rapid response times, fatigue resistance, superior thermal stability.

7 Anil Derivatives

Anil and its derivatives are a kind of photochromic compounds. They first experience a hydrogen transfer reaction and then experience a conformational change. They undergo a two-step reaction. The color change reaction is:

8 Polycyclic Quinone

Polycyclic quinones are a kind of compounds. Being exposed in ultraviolet light, it displays photochromism through an alkoxyl migration reaction. The color change reaction is:

Anthraquinone-based photochromic materials are a kind of new functional materials. It has some characteristics. One important characteristic is that its ana’trans reaction can be neglected as it nearly has no decolorization reaction at room temperature. The most important characteristic is that, with high reversible transformations, it can do reversible transformation for 500 times without damaging materials

9 Viologen

Viologens, i.e., N, N-dialkyl-4,4′-bipyridinium salts. The photochromic processes of photochromic processes also belong to pericyclic reactions. The color-changing is as follows:

Viologen compounds are a special kind of organics. By photochemical, electrochemical, chemical method, it can generate redox reactions. During the reaction, they exhibit apparent color changes. This kind of compounds has excellent redox properties.

10 Spirooxazines for Novel Organic Photochromic Material

Spirooxazine-based photochromic materials have similar color-changing mechanism to that of spiropyrans. They are a new kind of materials. They have sound properties. In common situation, when being exposed to ultraviolet light, the single bond between the oxygen atom and the spirocarbon atom and breaks. Hence, the molecule is transformed from the closed-ring form to an open-ring planar merocyanine structure (it is designated as PMC). After that, we can observe absorption in the visible region and a large conjugated system is formed. The spirocarbon atom dividing the molecule into a spiro-naphthoxazine ring and two nearly perpendicular indoline rings. The stable form of spirooxazines is a colorless closed-ring structure (denoted as SP). These rings are not conjugated and therefore we can observe no absorption in the visible region. The PMC rapidly goes back to the SP form after the UV light source are removed. Demo as below:

The Application of Photochromic Materials

(1) Information Storage Elements

The photochromic compounds can undergo cyclic color-changing under different wavelengths and intensities of light. They can realize the retention and erasure of information as long as they are produced into computer memory storage components. The components can quickly erase or write information. They have sound fatigue resistance with inconceivable density of recorded information.

This is new development orientation for new type of memory storage materials.

(2) Materials for decoration and protective packaging

Photochromic compounds can serve as ornamental products. It can be used in wallpapers, T-shirts, lacquered artworks, nail varnishes.

In order to ensure security and safeguard against solar radiation, we can integrate them into windscreens for vehicles and airplanes, dynamic glazing for architectural purposes, packaging films.We can add these compounds into auxiliary agents used in coatings, yielding screen-printable inks, coating formulations, ink, and diluents, typical binders. This process can meet different needs from customers.

(3) Self-developing holographic recording photography

It is a new self-developing dry photographic technique. It leverages the photosensitivity of photochromic materials to generate this photographic technique. There is a photochromic substance (such as spiropyran, fulgide, etc.). We can coat a thin layer of such substance on a support substrate like a transparent film. Such substance only responds to ultraviolet light but not responds to visible light. Such process can form a colored image. This imaging method offers high resolution, eliminates operational errors, and allows images to be recorded, erased, and rerecorded in reverse. This image can be recorded, erased in reverse. There will be no chance of operational errors and it is of high resolution.

(4) Military Applications

Photochromic materials can be used for the production of high-intensity light dosimeters, as they are extremely sensitive to intense light. Photochromic materials can be used to measure gamma rays, X-rays, ionizing radiation, doses of ultraviolet light. For example, if this kind of material is coated on the exterior of a spacecraft, the high radiation doses can be accurately and rapidly and measured. Photochromic materials have many other advantages. It can also be produced into multi-layer filters. By using such filters, we can prevent ultraviolet light from harming human eyes and skin. We can also regulate the intensity of radiation. If this kind of materials are coated on the weapons, for example, if we use such highly sensitive photochromic systems as indicator screens on weapons, the movements of warship and aircraft can be tracked. A temporary trace that can be erased will be formed.