Collapse of the Förster energy transfer in doped p -hexaphenylene thin films undergoing crystallization

A fluorescence resonant energy transfer study is presented, which uses composition-spread libraries of para -hexaphenylene doped with tris-(8-hydroxyquinolinato)aluminum(III) ( p 6 P : Al q 3 ) , prepared by a combinatorial physical vapor deposition technique. The p 6 P : Al q 3 libraries deposited at room temperature are polycrystalline and exhibit an inefficient energy transfer. The energy transfer efficiency increases significantly in amorphous p 6 P : Al q 3 libraries deposited at − 78 ° C , yielding the Förster transfer radius of 22 Å , in good agreement with the theory. The amorphous p 6 P : Al q 3 libraries undergo slow spontaneous crystallization at room temperature accompanied by a gradual collapse of the energy transfer.