Interactions of Functional Dyes

Functional dyes may be classified in several ways. Here, they are discussed according to their application. However, before doing this, it is pertinent to consider briefly the interactions of functional dyes with various agents. This enables a particular phenomena to be associated with each application. 

Functional dyes are designed to interact with electromagnetic radiation, pH, electricity, heat, pressure and even frictional forces. Each of these interactions is discussed, beginning with the most important interaction, that with electromagnetic radiation. 

Electromagnetic Radiation. Functional dyes interact with electromagnetic radiation in the near-UV (300-400 nm), visible (400-700 nm), and near-IR (700-1500 nm) to produce a variety of effects required for hi-tech applications. The more important effects are described briefly, including their main applications. 

As mentioned above most molecules lose energy from the excited state as heat. The most efficient molecules for converting electromagnetic radiation into heat are those that absorb in the near-IR region, i.e., infrared absorbers (IRAs). There has been much interest in IRAs because of their use in laser thermal transfer, optical data storage [the older write-once read-many (WORM) and the newer compact disc recordable (CD-R) and digital versatile disc recordable (DVD-R) systems], computer-to-plate printing, and as solar screens for car windscreens and windows. 

Thermochromic dyes change color with temperature (heat). The effect may be due to a single dye or a composite system, and the color change may be reversible or irreversible. Thermochromic dyes find use in direct thermal printing and as temperature sensors, as well as in clothing and novelties. 

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