Colorful chemistry is great, but luminescent chemistry is even better. This week we synthesized two luminescent compounds: Alq3 with q = 8-quinolinolate and Eu(tta)3(phen) with tta=theonyltrifluoracetone, phen = 1,10-phenantroline.
We tested the compounds under UV-light, where Alq3 emitted green light and Eu(tta)3(phen) red, due to fluorescence. The compounds would produce the same light in an electric field (electroluminescence), which is the basic principle behind OLED-displays, but unfortunately this requires a more complex setup.
Alq3 emits green light when radiated with UV-light. This is a typical main group luminescent compound, where the luminescence comes from π-π*-transitions in the conjugated system (the other common transition is n-π*. As the transitions take place in molecular orbitals, there is a large gap between the many vibrational states and the emission peak is broad. Also, it’s only slightly shifted from the absorption peak.
Eu(tta)3(phen) emits red light when radiated with UV-light. Eu is a rare-earth metal and the luminescence come from f–f-transitions on the metal. This gives very sharp emission-peaks (because the transitions take place in atomic orbitals), which is good. Also, the absorption peak is shifted a large difference from the absorption peak. This ensures the compound is really white when no stimuli is added, while Alq3 is slightly yellowish.
A fun fact is that an Europium (Eu) compound is used in the Euro banknotes for anti-counterfeiting.