TAILORING OF COLOR

Among challenges for tailoring of performance of CP LEDs are tailoring the color or emission to encompass the entire Visible spectral region. 

Electroluminescence spectra from P(PV) and two derivatives. After Reference [89], reproduced 

Perhaps one of the most elegant manifestations of tliis approach of using substituents or structures within a CP family to tailor bandgap, which in turn tailors color, has been seen in recent work of the Inganlis group [766, 767]. The structural variation, in a family of P(T) derivatives, and resultant electroluminescent spectra are 

Structures (top) and EL spectra (bottom) for P(T)-derivative LEDs, showing tailorability of color. After Reference [766, 767] reproduced with permission. 

Again using the same structural modification approach, the Cambridge group [768] synthesized the CN-thiophene derivative shown in Fig. 6-1 la. This very low bandgap material displayed the absorption, EL and PL spectra shown in Fig. 16-1 lb. and emitted well into the NIR, up to ca. 1000 nm. This CP, whose LUMO lay closer to the Fermi level of Ca than of Al, functioned well only with the former metal, in the 

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Another approach towards tailoring of color is of course discovery of entirely new, electroluminescent CPs which emit at different wavelengths. Such an approach has been demonstrated in more recent work by the Epstein group at Ohio State University [770, 771]. Thus, they have found that pOly(p-pyridine) emits blue light and poly(p-pyridyl vinylene) emits orange light. Many of these materials and devices are discussed in the section on AC-driven LEDs below. 

The introduction of auxochromes into the almost colorless anthraquinone permits the tailoring of compounds to cover nearly all shades of dye colors types and positions of the substituents in the molecule determine the hue. As a rule the bathochromic shift in simple anthraquinones increases with increasing basicity of the substituents. This generalization is clearly shown by the wavelengths of the longest wavelength absorption maximum of anthraquinones mono substituted in the 1-position [1] (Table 3.5) ... 

There is currently a trend to increase the multifunctional nature of color concentrates so that color as well as other desired properties are added to the resin system. This increases the processor s flexibility in meeting user s needs and simplifies user inventory by reducing the need to stock large quantities of tailored resins. 

When a direct current (dc) voltage is applied, the optical absorption characteristics of the compound change. The gain/loss of color occurs by the inclusion/elimination of the ion. In this case, the ion can be H, Li ", Na ", or Ag". The absorption characteristics of electrochromic materials can thus be tailored for specific applications simply by adjusting the applied voltage. 

A new line of highly visible and energetic polyester metallized foil films. Coated in a variety of vibrant colors, these sparkle colors can be used in graphic arts, paint, textile etnd plastics applications. These products are available in a wide range of colors and particle sizes, tailored to specific applications. The standard particle sizes are 0.4 nun and 0.1 mm square cut for Dazzle Colors. Smaller or larger sizes are available by special request. 

Derivatives of P(PV) continue to be the targets of choice for tailoring of LED emission color. For example, Yin et al. [769] described a unique derivative, poly(2,5-diphenyl-l,3,4-oxadiazolyl)-4,4 vinylene) (structure in Eflj 16J below), with a peak emission at 483 nm and a turn on voltage of 6 V in an ITO/CP/Al configuration. 

Identify and describe v th examples at least three methods which can be used to tailor the color of emission of CP LEDs. Can you suggest a way of having a CP LED emit several, selectable colors. 

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