Synthesis and properties of organic fluorescent molecules for blue to red conversion for LED systems using energy transfer

The efficiency of color conversion in remote phosphor light emitting diode (LED) applications can be improved by direct blue to red conversion instead of blue to yellow to red conversion. In this publication, two molecules that have chemically linked blue light absorbing donor and red emitting acceptor moieties were synthesized in which the blue to red conversion takes place via Forster resonance energy transfer (FRET). The properties of these so called “FRET molecules” were studied in poly(methyl methacrylate) (PMMA) films and compared with those of the parent yellow and red fluorescent molecules. The quantum efficiency (QE) of these films depends strongly on the chemical structure of the blue light absorbing moiety. The molecule with high QE showed an increased photochemical stability of the blue light absorbing moiety compared to that of the parent yellow fluorescent molecule and a decreased photochemical stability of the red emitting moiety compared to that of the parent red fluorescent molecule. • Compounds formed from 4 blue absorbers and one red emitter were synthesized. • Compounds showed color conversion from 450 to 620 nm. • Efficient energy transfer suppressed the yellow emission of the blue absorbers. • Energy transfer increased the photochemical stability of the blue absorber. • Materials may be used in color converters in highly efficient future LED systems