The origin of luminescence blueshifts in Alq₃ composites

Recently, tris(8-hydroxyquinoline)aluminum (Alq₃) has been diluted into various sol-gel matrices, and a strong blueshift with respect to the well-known emission band of amorphous thin films has been observed. This result has been explained by the absence of interactions among molecules that are isolated in the microscopic pores of glasses. The same explanation is also working in analogous measurements performed lately in various matrices, where the blueshift was wrongly attributed to a mixing of facial and meridianal isomers. Indeed, it is shown here that the Alq₃ meridianal isomer alone can explain the experimental results.