**2. Chromism**

In this text photochromism shall be addressed in a context of products of high added values. These high added values result from functionalities being added, thus moving away from the classical concept of a textile product. The differences between a classical and a high added value product are numerous; production process may be far technologically more demanding, number of functionalities may be increased significantly, technical applicability may be greater and finally the greatest difference may be between the price of production and that of an final product.

When discussing the term photochromic, one should first clear out the term "chromic". Chromism is a process that induces a reversible colour change of components consisting of a chemical compound. This includes changes on the molecular level like cleavage of the chemical bonds or changes on the level of molecular conformations. In most of the cases, chromism is based on changes ocurring inside of the molecule, among electrons. This especially implies "pi" and "d" electron positions so that the phenomenon is induced by various outside stimulus bearing the ability of altering electronic density of the compound or a substance (Lee, S. J. et al. 2006; Nakazumi, 1997).

It is well known that many of the natural compounds possess chromic property, while a number of artificial compounds of specifically characterized chromic properties have been synthesized so far (Shibahashi, 2004). Chromism refers to the phenomenon in which colour is the result of a broad spectral interactions among incident light and material (Bamfield, 2001). These interactions may be categorized into following five groups:


These chromic effects are caused by:


Phenomenon including a change in colour of a chemical compound is named according to external stimulus causing the reaction, either physically or chemically (Viková, 2004). Many, but not all of these reactions are reversible. The classification is as follows:


Described as such, the system bears all the necessary qualities of a smart textile. It is capable of alerting and protecting the wearer from the very specific threat as it has been specifically

From the textile engineer's, namely dyer's point of viewing things, not much has changed. Only the concept of "colour all the time" has changed to "colour at the right time" principle, which may be observed as one of the options of giving leverage to textile companies in search of means and ends of once again reclaiming the leader status on the worldwide market.

In this text photochromism shall be addressed in a context of products of high added values. These high added values result from functionalities being added, thus moving away from the classical concept of a textile product. The differences between a classical and a high added value product are numerous; production process may be far technologically more demanding, number of functionalities may be increased significantly, technical applicability may be greater and finally the greatest difference may be between the price of production

When discussing the term photochromic, one should first clear out the term "chromic". Chromism is a process that induces a reversible colour change of components consisting of a chemical compound. This includes changes on the molecular level like cleavage of the chemical bonds or changes on the level of molecular conformations. In most of the cases, chromism is based on changes ocurring inside of the molecule, among electrons. This especially implies "pi" and "d" electron positions so that the phenomenon is induced by various outside stimulus bearing the ability of altering electronic density of the compound

It is well known that many of the natural compounds possess chromic property, while a number of artificial compounds of specifically characterized chromic properties have been synthesized so far (Shibahashi, 2004). Chromism refers to the phenomenon in which colour is the result of a broad spectral interactions among incident light and material (Bamfield,

Phenomenon including a change in colour of a chemical compound is named according to external stimulus causing the reaction, either physically or chemically (Viková, 2004). Many,


designed, calibrated and optimized.

**2. Chromism** 

and that of an final product.





or a substance (Lee, S. J. et al. 2006; Nakazumi, 1997).



2001). These interactions may be categorized into following five groups:


but not all of these reactions are reversible. The classification is as follows:

izomerization among two different molecular structures


Over the past ten years, investigations on thermochromic pigments have gained popularity. These are aimed at obtaining new effects on dyed textile materials. Using a conventional technique of textile printing in combination with thermochromic pigment an intelligent textile is obtained. Intelligence is defined by the ability of the printed textile to change colour in accordance to the presence of an outside stimulus. In this case temperature changes ocurring within the close environment of the textile (Karlessi, et al. 2009; Kulčar et al., 2010; Maeda, S. 1999).

As far as quality of the chromic materials goes, it will depend on several parameters:

