Benzoselenadiazole-containing inhibitors of protein kinases were constructed and their capability to emit phosphorescence in the kinase-bound state was established. Labelling of the inhibitors with a red fluorescent dye led to sensitive responsive photoluminescent probes for protein kinase CK2 that emitted red light with a long (microsecond-scale) decay time upon excitation of the probes with a pulse of near-UV light.