A 20 mg ml -1 toluene solution of PDI-coVPy-2.5% was mixed with a 20 mg ml -1 toluene solution of polystyrene (MW ~ 35,000 g mol -1 , from Sigma Aldrich, St. Louis, MO, USA) at a ratio of 1/1000, v/v. The mixed solution was drop-casted onto a commercial UV LED (N3535