We relate the chemical structure of a series of methyl (Me) substituted group III metal tris(8-quinolinolato) chelates (nMeq(3)M: n = 0, 3, 4, 5; M = Al(3+), Ga(3+)) to their photoluminescence (PL), electroluminescence, and thermal properties. Methylation of the 8-quinolinol ligand at the 3 or 4 position (pyridyl ring) results in a factor of 1.4 and 3.0 enhancement of PL quantum efficiency (phi(PL)), respectively, whereas methylation at the 5 position (phenoxide ring) results in a factor of approximately 3.0 decrease in phi(PL) relative to the unsubstituted analogue. Electroluminescent quantum efficiencies of undoped organic light-emitting devices using the aluminum tris(8-quinolinolato) chelates are 1, 0.45, 1.4, and 0.80% for unsubstituted 5-, 4-, and 3-methyl-8-quinolinol ligands, respectively. Devices made with the latter two ligands have a higher operating voltage to generate the same current density. Similar trends were observed for methylation of gallium tris(8-quinolinolato) chelates. We relate these results to the thermal properties of the compounds measured by simultaneous differential scanning calorimetry and thermal gravimetric analysis. The C-4 methylated derivatives exhibit approximately 60 degrees C lower crystalline melting points than all other derivatives, indicating the weakest cohesive forces between molecules. Unlike Alq(3), both the C-4 and C-5 methylated derivatives show no recrystallization of the glassy state below 500 degrees C and exhibit approximately 20-25 degrees C higher glass transition temperatures. We infer that methylation of the 8-quinolinol ligand reduces intermolecular interactions and consequently impedes charge transport through the film.

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We have previously shown that diphenylpolyenes incorporating diphenylamino donor substituents form exceptionally stable bipolaronic dications in solution, even at the bis-(diphenylamino)-E-stilbene level, whereas most previously known polyenylic bipolarons were unstable at lengths shorter than the tetraene1. Most recently we have also demonstrated that replacement of one of the diphenylamino substituents in the stilbene substrate with a N-(hydroxyethyl), N-ethylaminophenyl group yields a functionalized polyene that can easily be attached to PMMA as a pendant group, or to 3,5-dihydroxy-benzyl alcohol to form reactive dendrons2. These functionalized materials also form extremely stable bipolarons and are intensely fluorescent. In this presentation we will discuss the formation of G-0 dendrimers incorporating a series of polyenes related to the stilbene structure, and possible photonic applications.