Colorless, Transparent, Dye-Doped Polymer Films Exhibiting Tunable Luminescence Color: Controlling the Dual-Color Luminescence of 2-(2′-Hydroxyphenyl)imidazo[1,2-a]pyridine Derivatives with the Surrounding Matrix

Colorless, transparent, polymer films including 2(2'-hydroxyphenyl)imidazo[1,2-a]pyridine (HPIP) derivatives, 1 and 2, are prepared by a spin-coating method. The observed emission spectra upon photoexcitation of these polymer films were composed of dual emission bands: the normal luminescence at 370-410 nm (purple) and the greatly Stokes-shifted emission at 520-580 nm (yellow) assigned as the excited-state intramolecular proton transfer (ESIPT) luminescence. Relative intensity of the two emissions varied according to the polymer matrices, resulting in change in the luminescent color of the dye-doped polymer films. Particularly, the luminescence properties of 6-cyano HPIP, 2, are highly susceptible to the surrounding environment, and therefore successfully tuned to produce a wide range of colors, from purple to orange, by changing its concentration within and the type of the polymer matrix. This observation can be ascribed to the formation of a relatively weak intramolecular hydrogen bond resulting from the electron-withdrawing 6-cyano group. Thus, we demonstrate large variations in emission color can be achieved using interactions of the single component with the surrounding matrix. These results offer promise as a convenient and effective method for a wide-range tuning the luminescence colors of dye-doped polymer films.