**3. Photochromism**

The phenomenon of photochromism is an analogue to all chromic processes. The change in colour is influenced by light in a reversible way (Fig. 1) (Cheng, 2007). Uncoloured material doesn't absorb light and may only be activated by energetically rich photons of the near UV electromagnetic spectra. Many of the inorganic materials such as copper, mercury, various metal oxides and some minerals exhibit the photochromic phenomenon (Van Gemert, 1999a, b). However, their use is considered inappropriate for textile materials and substrates. Organic molecules such as spiropyrans, spirooxazines and fulgides are suitable for use on textiles (Bouas-Laurent & Dürr 2001).

From Murex Purpura to Sensory Photochromic Textiles 61

Murex and Purpura Snails

immerse the wool or silk 5 hours

N

N

Br <sup>H</sup>

Fig. 2. Preparation of the dye obtained from Murex

level is given in figure 2 (Durr & Bouas-Laurent, 1990).

storage and security applications (Hampp, 2005a, b).

**3.2 Demands on photochromic system** 

O

Br <sup>H</sup>

O

salt water 3 days, boil 10 days,

> SMe N H

> > N H

> > > O

Brief description on preparation of the dye and chemical change occurring on molecular

As far as natural photochromic dyes go, rhodopsin is considered a photosensitive compound of reversible colour capacity. It is present in retina of the eye. Activating mechanism of rhodopsin is of photochromic triggering mechanism. Activated by light, it produces a nerve stimulus, transmitted to the cortex to provide visual perception. Rhodopsin has been discovered inside primitive bacterium, Halobacterium halobium. In it, it is responsible of transforming sunlight into energy, which classifies metabolism. Technical applications of rhodopsin, considered as photoswitchable biomaterial include optical data

Investigations on photochromics on scientific level date back to 19th century. It was J. Fritzsche who first noticed photochromic property of a solution of tetracene, while later on E. Ter Meer

1. Development of colour in photochromic systems – in order of being classified a sensor, the dynamics of colour development must be a rapid reaction to source of UV light 2. Return to the rest state (colourless) – the rate of fading of the system has to be controllable

3. Wide palette of colours – range of the colours being exhibited as a result of irradiation

4. Rest state in which colour is not exhibited – the state in which there is no excitement of the electrons, caused by an external stimuli should be as colurless as possible Photochromic dye appropriately applied onto textile material forms a photochromic system, which in case of fulfilling the abovementioned demand is in fact a sensor (Billah, 2008).

and all possible influences, such as influence of heat or sunlight, investigated

noticed it on solid potassium salt of dinitromethane (Bouas-Laurent & Dürr 2001).

Ideally, any organic photochromic system should be of following qualities:

by UV light should be across the visible range of light

Br

Br

+ Mes

MeS O

sunlight/air

#### Fig. 1. Mechanism of photochromism

The very principle, the triggering mechanism of photochromism is as follows: chemical compound transitions from form A into a form B, each of them of a specific absorption spectra implying specific colouring of the form, as well. The triggering mechanism is UV light induced (process of activation). As a result of incident UV light, compound changes its colour (Bouas-Laurent & Dürr 2001).

$$\text{A (colourless)} \vdash h\nu\_1 \to \text{B (colourred)}\tag{1}$$

Upon removal of the light source the colouring disappears as the molecule return to their inactivated state i.e. rest state. Deactivation is usually a slower process than activation and hysteretic behavior is noted. In terms of the dynamics of deactivation, visible light spectra and heat increase it, while polar solvents decrease it. Colouring is usually of lower intensity at higher temperatures i.e. reversing proportionate.

$$\text{A (coloured)} \vdash h\nu\_2 \to \text{B (colourless)}\tag{2}$$

By definition, discolouring of the chemical compound caused by UV part of the electromagnetic spectra is called negative photochromism.

There are three different groups of chemical processes on which the transformation of form A into form B is based:


These reactions have to be reversible in order to be characterized as photochromic. Otherwise, the reaction may be observed as usual metameric reaction (Bouas-Laurent & Dürr 2001).

#### **3.1 Historical overview**

The phenomenon of colour changing compound has been noticed and used for millennia. The first known, written documentation is that on Tyrian purple, dating 350 years B.C. i.e. back to the times of Alexander the Great. Dye was obtained from sea snails (Murex Brandaris and Murex Purpura). Applied onto textile material, the dye is in its uncoloured form and reveals true colouring only after being exposed to sunlight.

The very principle, the triggering mechanism of photochromism is as follows: chemical compound transitions from form A into a form B, each of them of a specific absorption spectra implying specific colouring of the form, as well. The triggering mechanism is UV light induced (process of activation). As a result of incident UV light, compound changes its

 A (colourless)+ *hν<sup>1</sup>* → B (coloured) (1) Upon removal of the light source the colouring disappears as the molecule return to their inactivated state i.e. rest state. Deactivation is usually a slower process than activation and hysteretic behavior is noted. In terms of the dynamics of deactivation, visible light spectra and heat increase it, while polar solvents decrease it. Colouring is usually of lower intensity

 A (coloured)+ *hν<sup>2</sup>* → B (colourless) (2) By definition, discolouring of the chemical compound caused by UV part of the

There are three different groups of chemical processes on which the transformation of form

These reactions have to be reversible in order to be characterized as photochromic. Otherwise, the reaction may be observed as usual metameric reaction (Bouas-Laurent &

The phenomenon of colour changing compound has been noticed and used for millennia. The first known, written documentation is that on Tyrian purple, dating 350 years B.C. i.e. back to the times of Alexander the Great. Dye was obtained from sea snails (Murex Brandaris and Murex Purpura). Applied onto textile material, the dye is in its uncoloured

Fig. 1. Mechanism of photochromism

colour (Bouas-Laurent & Dürr 2001).

A into form B is based: - Trans-cis isomerization

**3.1 Historical overview** 

Dürr 2001).

at higher temperatures i.e. reversing proportionate.

electromagnetic spectra is called negative photochromism.


form and reveals true colouring only after being exposed to sunlight.

Fig. 2. Preparation of the dye obtained from Murex

Brief description on preparation of the dye and chemical change occurring on molecular level is given in figure 2 (Durr & Bouas-Laurent, 1990).

As far as natural photochromic dyes go, rhodopsin is considered a photosensitive compound of reversible colour capacity. It is present in retina of the eye. Activating mechanism of rhodopsin is of photochromic triggering mechanism. Activated by light, it produces a nerve stimulus, transmitted to the cortex to provide visual perception. Rhodopsin has been discovered inside primitive bacterium, Halobacterium halobium. In it, it is responsible of transforming sunlight into energy, which classifies metabolism. Technical applications of rhodopsin, considered as photoswitchable biomaterial include optical data storage and security applications (Hampp, 2005a, b).

Investigations on photochromics on scientific level date back to 19th century. It was J. Fritzsche who first noticed photochromic property of a solution of tetracene, while later on E. Ter Meer noticed it on solid potassium salt of dinitromethane (Bouas-Laurent & Dürr 2001).

#### **3.2 Demands on photochromic system**

Ideally, any organic photochromic system should be of following qualities:


Photochromic dye appropriately applied onto textile material forms a photochromic system, which in case of fulfilling the abovementioned demand is in fact a sensor (Billah, 2008).

From Murex Purpura to Sensory Photochromic Textiles 63

A large number of substituents are possible for spiropyran ring. Pyran ring is most often substituted benzo or naphtopyran. Heterocylic component can be varied, as a long list of ring systems is available: indole, benzthiazole, benzoxazole, benzselenozole, quinoline, acridine, phenathridine, benzopyran, naphtopyran, xanthenes, pyrolidine and thiazolidine.

Synthetic pathway to spiroindolinobenzopyrans (Figure 4.) begins with synthesis of Fischer's Base (1.5 - 1.6). Spiroindloino compound is an obtained by condensation of Fisher's base (1.6; R=alkyl) with salicyaldehyde (1.7.). Another route of synthesis may be with indolinium compound bearing different N-alkyl groups (1.6; R=alkyl) and different ring substituents; chemical reaction of synthesis is shown in Figure 4 by alkylation of a 2-

N

CHO

(1.7)

(1.5)

n +

R

OH

+

O


(1.8)

CH3

CH3

X -

**3.4.1 Synthesis of spiroindolinobenzopyrans** 

methylindole to obtain (1.8.; R=alkyl) (Keum et al., 2007).

Fig. 4. Synthetic pathway to BIPS and derivatives

obtained (Clarke, 1995).

N H

CH3

CH3

N

R

(1.6)

CH3

R +

CH2

OH-

RX

N R

6-nitro-1',3',3'-trimethylspiro [2H-1-benzopyran-2,2'-indoline] (6-nitro-BIPS) may be considered to be most studied of all spiro-organic photochromics. Therefore, its synthesis shall b e described thoroughly. Description refers to a slightly modified literature method (Inoue et al., 10968; Sivadjian 1968). Fischer's base, 1,3,3-methyleneindoline (3,5 g; 0,02 mol) is dissolved 40 ml of absolute methanol. To this solution, 3,35 g of 2-hydroxy-4 nitrobenzaldehyde (0,02 mol) in small proportions is added over the period of 10-15 minutes. The obtained pink-brown solution is refluxed for 2 h. The reaction mixture evaporated to a small volume in an air draft. Fine powder is collected by filtration and washed with absolute ethanol and than air-dried. This was recrystallized from boiling nhexane with a small amount of activated charcoal. Pale yellow microcrystalline powder is

+

R CH3

Sensor capable of reacting to UV light of exactly defined spectra and intensity in a preprogrammed, controllable manner. Described as such, system alerts and protects the wearer against negative influence of UV irradiation and classifies the very definition of a "smart textile". Having fulfilled all of these demands, investigations should be made to find out whether any derived qualities have arisen as a result of applying photochromic molecules onto textile fibres. These qualities may be an increment in UPF (Ultraviolet Protection Factor), a very interesting value for light fabrics in which bear constructional characteristics, such as the type and density of weave cannot provide satisfying UV-R protection. Another interesting quality could be certain antibacterial or antifungal properties added onto textile materials (Bamfield, 2001).

#### **3.3 Classes of photochromic compounds**

Photochromic compounds can be divided into five main classes fitting the requirements of an ideal photochromic compounds. These are, as follows:


In terms of applicability to textile fibres, spiropyrans, spironaphtoxazines and chromenes have been found as most suitable considering fatigue, life time and fastness properties. Therefore, this paper will cover physic-chemical properties of these classes of dyes, suitability of use on natural and man-made fibres and several technological techniques of application.

#### **3.4 Spirobenzopyrans**

This is a widely studied class of photochromic compounds. They are consisted of a pyran ring, in most cases 2H-1-bezopyran and heterocyclic ring (Fig. 3). Link between the rings is a common spiro group (1.1). The mechanism by which the photochromism occurs is actually cleavage of the carbon-oxygen bond, caused exclusively by irradiation with UV light. The result is a ring-opened coloured species, called "merocyanine" form or MC, which can be cis-(1.2), trans–(1.3) or ortho-quinoidal form 1.4 (Bamfield, 2001, Oda, 2008).

Fig. 3. Spiroindolinobenzopyran and ring opened merocyanine quinonoid form

Sensor capable of reacting to UV light of exactly defined spectra and intensity in a preprogrammed, controllable manner. Described as such, system alerts and protects the wearer against negative influence of UV irradiation and classifies the very definition of a "smart textile". Having fulfilled all of these demands, investigations should be made to find out whether any derived qualities have arisen as a result of applying photochromic molecules onto textile fibres. These qualities may be an increment in UPF (Ultraviolet Protection Factor), a very interesting value for light fabrics in which bear constructional characteristics, such as the type and density of weave cannot provide satisfying UV-R protection. Another interesting quality could be certain antibacterial or antifungal properties added onto textile

Photochromic compounds can be divided into five main classes fitting the requirements of

In terms of applicability to textile fibres, spiropyrans, spironaphtoxazines and chromenes have been found as most suitable considering fatigue, life time and fastness properties. Therefore, this paper will cover physic-chemical properties of these classes of dyes, suitability of use on

This is a widely studied class of photochromic compounds. They are consisted of a pyran ring, in most cases 2H-1-bezopyran and heterocyclic ring (Fig. 3). Link between the rings is a common spiro group (1.1). The mechanism by which the photochromism occurs is actually cleavage of the carbon-oxygen bond, caused exclusively by irradiation with UV light. The result is a ring-opened coloured species, called "merocyanine" form or MC, which can be

> N O + CH3

> > O

CH CH <sup>3</sup> <sup>3</sup>

N + CH3

CH CH3 <sup>3</sup>

natural and man-made fibres and several technological techniques of application.

cis-(1.2), trans–(1.3) or ortho-quinoidal form 1.4 (Bamfield, 2001, Oda, 2008).

(1.1.) (1.2.)

Colourless Coloured

(1.4.) (1.3.)

Fig. 3. Spiroindolinobenzopyran and ring opened merocyanine quinonoid form

N O CH3

O

CH CH3 <sup>3</sup>

N CH3

CH CH3 <sup>3</sup>

materials (Bamfield, 2001).

2. Spironaphtoxazines

**3.4 Spirobenzopyrans** 

4. Fulgides 5. Diarylethenes

3. Naphtopyrans (Chromenes)

**3.3 Classes of photochromic compounds** 

1. Spiropyrans (Spiroindolinobenzopyrans)

an ideal photochromic compounds. These are, as follows:

A large number of substituents are possible for spiropyran ring. Pyran ring is most often substituted benzo or naphtopyran. Heterocylic component can be varied, as a long list of ring systems is available: indole, benzthiazole, benzoxazole, benzselenozole, quinoline, acridine, phenathridine, benzopyran, naphtopyran, xanthenes, pyrolidine and thiazolidine.

#### **3.4.1 Synthesis of spiroindolinobenzopyrans**

Synthetic pathway to spiroindolinobenzopyrans (Figure 4.) begins with synthesis of Fischer's Base (1.5 - 1.6). Spiroindloino compound is an obtained by condensation of Fisher's base (1.6; R=alkyl) with salicyaldehyde (1.7.). Another route of synthesis may be with indolinium compound bearing different N-alkyl groups (1.6; R=alkyl) and different ring substituents; chemical reaction of synthesis is shown in Figure 4 by alkylation of a 2 methylindole to obtain (1.8.; R=alkyl) (Keum et al., 2007).

Fig. 4. Synthetic pathway to BIPS and derivatives

6-nitro-1',3',3'-trimethylspiro [2H-1-benzopyran-2,2'-indoline] (6-nitro-BIPS) may be considered to be most studied of all spiro-organic photochromics. Therefore, its synthesis shall b e described thoroughly. Description refers to a slightly modified literature method (Inoue et al., 10968; Sivadjian 1968). Fischer's base, 1,3,3-methyleneindoline (3,5 g; 0,02 mol) is dissolved 40 ml of absolute methanol. To this solution, 3,35 g of 2-hydroxy-4 nitrobenzaldehyde (0,02 mol) in small proportions is added over the period of 10-15 minutes. The obtained pink-brown solution is refluxed for 2 h. The reaction mixture evaporated to a small volume in an air draft. Fine powder is collected by filtration and washed with absolute ethanol and than air-dried. This was recrystallized from boiling nhexane with a small amount of activated charcoal. Pale yellow microcrystalline powder is obtained (Clarke, 1995).

From Murex Purpura to Sensory Photochromic Textiles 65

Spironaphtoxazines are a very interesting group of compounds that can be used on textile fibres (Billah, 2008; Lee, E. et al. 2008). This is because of their increased fatigue and resistance towards photodegradation. Structurally, they are nitrogen containing analogues of the spiropyrans. Photochromic reaction of opening spironaphtoxazine ring (Son et al.

Colourless Coloured (+ isomers)

The synthetic pathway to spironaphtoxazines is based on reaction between 1-hydroxy-2 nitroso bearing aromatic ring and 2-alkylidene heterocycle, such as Fischer's base (1.6; R=H). Naphtoxazines may be chosen from a list of substituents as the stability of nitrosonaphtols starting materials are much more stable than the nitrosophenols required for the parent benzo analogue (Coimbra, 2005). Synthetic pathway of obtaining alkyl substituted naphtoxazines, benzo- and heterobenzo-annulated derivatives is shown in Figure 6. Aqueous solution of corresponding phenolate and sodium nitrate is acidified. Heating the mixture in methanol under reflux gives condensation of nitrosonaphthols

OH

Most important positions for substitution, affecting colour and fatigue are the 5-position and 6'-position, responsible for both colour properties (expressed as OD-optical density) and molar coefficient coefficient. The substituent on the 1-position has a kinetic effect on the rate of loss of colour back to the rest state. Important thing achieved by described syntheses are overcome colour range issues (550 – 620 nm). Important bearing amino substituents on 6'-position are synthesized from 4-substituted-1-nitroso-2–naphtols (1.14), prepared from

(1.6; R=H) reflux, MeOH

N O

(1.10)

N N

CH3

O

O

CH3

(1.11)

N

1

<sup>3</sup>CH CH3

5

N

6'

<sup>3</sup>CH CH3

2007a, b) derivative to its MC form is shown in Figure 5 (Bamfield, 2001).

O

CH3

N

Fig. 5. Spironaphthoxazine photochromic forms

**3.5.1 Synthesis of spiroindolinonaphtoxazines** 

NaNO2/NaOH aq. H2SO4

Fig. 6. Synthetic route to spiroindolinoaphthoxazine

<sup>3</sup>CH CH3

N

**3.5 Spironaphtoxazines** 

with indolines.

OH

(1.12) via (1.13) (Fig. 7).

1. 2.

The route to 1,3,3-trimethyl-spiro[indoline-2,3'-[3H]napht[2,1-b][1,4]oxazine (NISO) is quite similar. Stechiometric compaunds of Fischer's base and 1-nitroso-2-naphtol are refluxed in alcohol or toluene for 2-4 hours (Ono and Asada, 1970). Product is collected by filtration, washed with alcohol and air-dried. It is recrystallized from boiling n-hexane with a small amount of activated charcoal. A pale greenish powder was obtained. Both Qiso and BISO can be prepared by similar methods (Hurditch & Kwak, 1987).

#### **3.4.2 Spectral properties of spiroindolinobenzopyrans**

MC form of the spiropyran dyes shows great absorbance in the visible region of the spectrum, typical of merocyanine dyes. This open chain form of the molecule is thermally instable; therefore a rapid scanning absorption spectrophotometer must be used to measure absorption within visible spectrum. Polarity of the solvent plays a key role in preparation of the spiroindolinobenzopyrans as it shifts max of the solutions. Use of non-polar organic solvent is preferable as the compounds aren't water soluble. These classes of compounds are of strongly positive solvatochromic effect, which can be seen from the changing shape of the absorption curve and its position moving hypsochromically as the solvent polarity increases (Suppan & Ghonheim, 1997). In table 1. the changes of max in closed (SP) and open (MC) form of the NISO, as a result of solvent polarity are shown (Keum et al., 2007).


Table 1. The changes of max in closed (SP) and open (MC) form of the NISO depending on solvent polarity

Also, parent substituents play a key role in max changes of spiroindloinobenzopyran; especially in the 3,6,8-positions. From the table 2. it can be seen that they have the biggest influence on spectral properties of the coloured form of the spiroindolinobenzopyran.


Table 2. Absorption maximum of the coloured form of substituted BIPS (in ethanol)

#### **3.5 Spironaphtoxazines**

64 Textile Dyeing

The route to 1,3,3-trimethyl-spiro[indoline-2,3'-[3H]napht[2,1-b][1,4]oxazine (NISO) is quite similar. Stechiometric compaunds of Fischer's base and 1-nitroso-2-naphtol are refluxed in alcohol or toluene for 2-4 hours (Ono and Asada, 1970). Product is collected by filtration, washed with alcohol and air-dried. It is recrystallized from boiling n-hexane with a small amount of activated charcoal. A pale greenish powder was obtained. Both Qiso and BISO

MC form of the spiropyran dyes shows great absorbance in the visible region of the spectrum, typical of merocyanine dyes. This open chain form of the molecule is thermally instable; therefore a rapid scanning absorption spectrophotometer must be used to measure absorption within visible spectrum. Polarity of the solvent plays a key role in preparation of the spiroindolinobenzopyrans as it shifts max of the solutions. Use of non-polar organic solvent is preferable as the compounds aren't water soluble. These classes of compounds are of strongly positive solvatochromic effect, which can be seen from the changing shape of the absorption curve and its position moving hypsochromically as the solvent polarity increases (Suppan & Ghonheim, 1997). In table 1. the changes of max in closed (SP) and open (MC)

max of the closed SP form of NISO [nm] max of the open form

Hexan 560

Ethanol Methanol Methylene Chloride Hexane Solvent max [nm] 345 345 346 347 Ethanol 610 317 317 317 319 Acetone 600 297 303 302 303 Toluene 590

Table 1. The changes of max in closed (SP) and open (MC) form of the NISO depending on

Also, parent substituents play a key role in max changes of spiroindloinobenzopyran; especially in the 3,6,8-positions. From the table 2. it can be seen that they have the biggest influence on spectral properties of the coloured form of the spiroindolinobenzopyran.

R1

(1.9)

N

R1 R2 R3 R4 max [nm]

Table 2. Absorption maximum of the coloured form of substituted BIPS (in ethanol)

OCH3 OCH3 NO2 H NO2

2,2' 5'

R4

8 O <sup>6</sup> 3 4

R3

R4

H Ph Ph H H

MC of NISO [nm]

form of the NISO, as a result of solvent polarity are shown (Keum et al., 2007).

can be prepared by similar methods (Hurditch & Kwak, 1987).

**3.4.2 Spectral properties of spiroindolinobenzopyrans** 

solvent polarity

Ph H H H H

NO2 NO2 OCH3 NO2 H

Spironaphtoxazines are a very interesting group of compounds that can be used on textile fibres (Billah, 2008; Lee, E. et al. 2008). This is because of their increased fatigue and resistance towards photodegradation. Structurally, they are nitrogen containing analogues of the spiropyrans. Photochromic reaction of opening spironaphtoxazine ring (Son et al. 2007a, b) derivative to its MC form is shown in Figure 5 (Bamfield, 2001).

#### **3.5.1 Synthesis of spiroindolinonaphtoxazines**

Fig. 5. Spironaphthoxazine photochromic forms

The synthetic pathway to spironaphtoxazines is based on reaction between 1-hydroxy-2 nitroso bearing aromatic ring and 2-alkylidene heterocycle, such as Fischer's base (1.6; R=H). Naphtoxazines may be chosen from a list of substituents as the stability of nitrosonaphtols starting materials are much more stable than the nitrosophenols required for the parent benzo analogue (Coimbra, 2005). Synthetic pathway of obtaining alkyl substituted naphtoxazines, benzo- and heterobenzo-annulated derivatives is shown in Figure 6. Aqueous solution of corresponding phenolate and sodium nitrate is acidified. Heating the mixture in methanol under reflux gives condensation of nitrosonaphthols with indolines.

Fig. 6. Synthetic route to spiroindolinoaphthoxazine

Most important positions for substitution, affecting colour and fatigue are the 5-position and 6'-position, responsible for both colour properties (expressed as OD-optical density) and molar coefficient coefficient. The substituent on the 1-position has a kinetic effect on the rate of loss of colour back to the rest state. Important thing achieved by described syntheses are overcome colour range issues (550 – 620 nm). Important bearing amino substituents on 6'-position are synthesized from 4-substituted-1-nitroso-2–naphtols (1.14), prepared from (1.12) via (1.13) (Fig. 7).

From Murex Purpura to Sensory Photochromic Textiles 67

Both benzo and naphotpyrans are based on 2H-chromene ring system (Figure 9). These systems can be divided: 2H-benzopyrans (1.18) and three isomers of napohtopyrans (1.19- 1.21). Due to the little or no photochromic behavior, isomer in 1.21 will not be discussed. Although substituents on R1 and R2 position may be a part of carbocyclic spiro ring, they are usually unconnected substituents such as gem dialkyl or aryl groups (Pardo,

O

(1.20)

R1 R2

O

+

O

(1.21)

R1 R2

**3.6 Benzo and naphtopyrans (chromenes)** 

O

(1.19)

O

**3.6.1 Synthesis of benzopyrans and naphtopyrans** 

Fig. 10. Photochromic behavior of chromenes

R1 R2

Fig. 9. Chemical structure of 2H-benzopyrans and three isomers of napohtopyrans

In terms of photochromic mechanism, it is quite similar to that of spiropyrans shown in Figure 10. Presence of UV irradiation induces cleavage of C-O ring, thus breaking the pyran ring and giving zwitterionic form or more likely cis- and trans-quinoidal forms (1.16). Studies on the dynamics of the reaction have shown that formation of cis-quinoidal form occurs in picoseconds, followed by trans-form in nanosecond. Isomers (1.19) and (1.20) show quite different photochromic behavior. Isomer (1.20; R1,R2=Ph) produces a more bathochromic coloured activated state than (1.19; R1, R2=Ph) (max = 481 nm vs 432 nm), a large increment in colouration, but a very slow fade rate back to the inactivated

O O

trans-quinoidal cis-quinoidal

The synthetic method for more important 2,2-diaryl derivatives (1.25) involves the reaction of 1,1-diarylprop-2-yn-1-ol (1.24) with a substituted phenol or naphtol in the presence of acid catalyst. The alkynols are prepared by reaction of benzophenone (1.22) with Na or Li

derivative of an alkynide, such as the trimethylsilyil acetylide (1.23), Figure 11.

heat -

h

2010).

state.

O

(1.18)

R1 R2

Fig. 7. Analysis of position 5 and 6' in synthetic route to spiroindolinoaphthoxazine

#### **3.5.2 Spectral properties of spiroindolinonaphtoxazines**

The max of the ring opened spiroindolinonaphtoxazine is at 590 nm. Also, they show a negative solavtochromic shift. Absorption moves hypsochromically (20-60 nm) in less polar solvents (Kim, 2007), Figure 8.

Fig. 8. Synthetic pathway to spiroindolinopyridobenzoxazines

Commercially important group of spiroxazines are those in which the naphthalene ring is replaced by quinoline to give spiroindolinopyridinobenzoxazines (1.17) (Suh et al. 2007). Synthesis is a reaction between 5-nitroso-6 hydroxyquinoline (1.16) with alkyl substituted 2 methlenindolines (1.15). The data on absorption effects caused by substitution on 5- and 6' position are given in table 3.


Table 3. Substituent effects on the absorption maximum of the coloured state of spiroindolinonaphthoxazines

#### **3.6 Benzo and naphtopyrans (chromenes)**

66 Textile Dyeing

O

NR2

(1.12) (1.13) (1.14)

The max of the ring opened spiroindolinonaphtoxazine is at 590 nm. Also, they show a negative solavtochromic shift. Absorption moves hypsochromically (20-60 nm) in less polar

Fig. 7. Analysis of position 5 and 6' in synthetic route to spiroindolinoaphthoxazine

O

NH2OH

R2

R3

OH

NR2

N

R1

N

O N

CH CH3 <sup>3</sup>

NO

O

O

R2NH

**3.5.2 Spectral properties of spiroindolinonaphtoxazines** 

OH

Fig. 8. Synthetic pathway to spiroindolinopyridobenzoxazines

+

NO

(1.15) (1.16) (1.17)

Commercially important group of spiroxazines are those in which the naphthalene ring is replaced by quinoline to give spiroindolinopyridinobenzoxazines (1.17) (Suh et al. 2007). Synthesis is a reaction between 5-nitroso-6 hydroxyquinoline (1.16) with alkyl substituted 2 methlenindolines (1.15). The data on absorption effects caused by substitution on 5- and 6'-

O

CH3

N

Table 3. Substituent effects on the absorption maximum of the coloured state of

1

3CH CH3

5

N

6' - substituent 5 - substituent max [nm] H H 605 Indolino H 592 Indolino OCH3 623 Indolino Peperidino 637 Piperidino H 578 Piperidino Cl 568 Piperidino CF3 560 Morphilino H 580 Diethylamino H 574

6'

SO3Na

solvents (Kim, 2007), Figure 8.

position are given in table 3.

spiroindolinonaphthoxazines

CH3 CH2

<sup>3</sup>CH

R2

R3

Both benzo and naphotpyrans are based on 2H-chromene ring system (Figure 9). These systems can be divided: 2H-benzopyrans (1.18) and three isomers of napohtopyrans (1.19- 1.21). Due to the little or no photochromic behavior, isomer in 1.21 will not be discussed. Although substituents on R1 and R2 position may be a part of carbocyclic spiro ring, they are usually unconnected substituents such as gem dialkyl or aryl groups (Pardo, 2010).

Fig. 9. Chemical structure of 2H-benzopyrans and three isomers of napohtopyrans

In terms of photochromic mechanism, it is quite similar to that of spiropyrans shown in Figure 10. Presence of UV irradiation induces cleavage of C-O ring, thus breaking the pyran ring and giving zwitterionic form or more likely cis- and trans-quinoidal forms (1.16). Studies on the dynamics of the reaction have shown that formation of cis-quinoidal form occurs in picoseconds, followed by trans-form in nanosecond. Isomers (1.19) and (1.20) show quite different photochromic behavior. Isomer (1.20; R1,R2=Ph) produces a more bathochromic coloured activated state than (1.19; R1, R2=Ph) (max = 481 nm vs 432 nm), a large increment in colouration, but a very slow fade rate back to the inactivated state.

Fig. 10. Photochromic behavior of chromenes

#### **3.6.1 Synthesis of benzopyrans and naphtopyrans**

The synthetic method for more important 2,2-diaryl derivatives (1.25) involves the reaction of 1,1-diarylprop-2-yn-1-ol (1.24) with a substituted phenol or naphtol in the presence of acid catalyst. The alkynols are prepared by reaction of benzophenone (1.22) with Na or Li derivative of an alkynide, such as the trimethylsilyil acetylide (1.23), Figure 11.

From Murex Purpura to Sensory Photochromic Textiles 69

OMe

OMe

O

R1 R2 max IOD IODF10% Solvent H H 475 0,20 50 A MeO H 456 1,89 7 A H MeO 502 0,55 41 A H H 475 0,12 45 B MeO H 456 1,42 10 B Piperidino H 452 1,95 11 B Piperidino H 452 1,95 13 B Table 5. Influence of substituents in 6- and 8-positions on the properties of 3,3-diaryl-3H-

IODF10 - percentage loss in initial optical density 10s after removing UV irradiation source

Photochromic compounds as the ones represented in this chapter are commercially available from a number of suppliers, such as: Sigma Aldrich, PPG Industries and James Robinson. So far, virtually all application techniques have been investigated in efforts of functionalizing the textile fiber with photochromic systems. Some application methods have been proven advantageous over the other, such as embedding into the polymer matrix in the spinning phase of the "man-made" fibers (polypropylene). Other processes may include dyeing and screen printing, which are considered more appropriate since the demand on photochromic textiles is limited to piece garments, rather than to batch production (Billah, 2008; Canal,

The group of authors of this chapter has made significant efforts in functionalizing textile fibres with photochromic dyes. Therefore, this chapter will give a review of several papers covering this issue, namely application of photochromic compounds using the means of exhaust dyeing. In the context of dyeing technology, photochromic compounds may be observed as disperse dyes appropriate for dyeing "man-made" fibres. The dyeing process

Most of the investigation were done using Sigma Aldrich dyes of 97% purity and alterations

on the level of the dye molecule were made. Selected dyes are shown in the Table 6.

OD – the change in optical density (absorbance) on exposure to the xenon light source t1/2 – fade rate, time expressed in seconds for the OD to return to half of its equilibrium

1

R 2

8

6

R 1

naphtho[2,1-b]pyrans (A = polyurethane; B = Spectralite)

**4.1 Exhaust dyeing with photochromic compounds** 

max – refers to the absorption maximum of the coloured state

Whereas:

value.

**4. Textile applications** 

2008; Nelson, 2002).

has to be set accordingly.

Fig. 11. Synthesis of diaryl benzo- and naphtopyrans

### **3.6.2 spectral and physical properties of diarylnaphtopyrans**

Like the classes of spirobenzopyrans and spironaphtoxazines, diarylnaphtopyrans show significant solvatochromic behaviour. Influence of the substituents in the 3-phenyl rings on the properties of 3,3-diaryl-3H-naphto[2,1-pyrans] (tab. 4 and 5).


Table 4. Influence of substituents in the 3-phenyl rings on the properties of 3,3-diaryl-3Hnaphto[2,1-b]pyrans (A = toluene solution; B = imbibed into diethyleneglycol bis(allyl carbonate) polymer)


Table 5. Influence of substituents in 6- and 8-positions on the properties of 3,3-diaryl-3Hnaphtho[2,1-b]pyrans (A = polyurethane; B = Spectralite)

Whereas:

68 Textile Dyeing

Me3Si

, <sup>+</sup> - <sup>M</sup> <sup>+</sup>

(1.23)

O

(1.25)

Like the classes of spirobenzopyrans and spironaphtoxazines, diarylnaphtopyrans show significant solvatochromic behaviour. Influence of the substituents in the 3-phenyl rings on

O

R1 R2 max OD T1/2[s] Solvent H H 430 - 11 A H 4-MeO 458 - 8 A H 4-CF3 422 - 28 A 4-MeO 4-MeO 475 - 3 A 4-MeO 4-CF3 440 - 4 A 4-MeO 4-NMe2 512 - 1 A 4-NMe2 4-NMe2 544 - 0,5 A H H 0,36 45 B 2-F 4-MeO 456 1,0 170 B 2-F 3,4-diMeO 472 1,05 203 B 2-Me 4-MeO 469 2,40 600 B 2,6-diF2 4-MeO 450 2,23 1800 B Table 4. Influence of substituents in the 3-phenyl rings on the properties of 3,3-diaryl-3Hnaphto[2,1-b]pyrans (A = toluene solution; B = imbibed into diethyleneglycol bis(allyl

R

O

Ar Ar

(1.22)

Fig. 11. Synthesis of diaryl benzo- and naphtopyrans

carbonate) polymer)

**3.6.2 spectral and physical properties of diarylnaphtopyrans** 

the properties of 3,3-diaryl-3H-naphto[2,1-pyrans] (tab. 4 and 5).

Ar Ar

R1

R2

OH

<sup>R</sup> 1. acid cat. 2. heat

Ar Ar OH

(1.24)

SiMe3

IODF10 - percentage loss in initial optical density 10s after removing UV irradiation source max – refers to the absorption maximum of the coloured state

OD – the change in optical density (absorbance) on exposure to the xenon light source t1/2 – fade rate, time expressed in seconds for the OD to return to half of its equilibrium value.
