Indirubin, also known as isoindigotin, is an inhibitor of cyclin-dependent kinases (CDK1/cyclin B (IC50 = 10µM), CDK2/cyclin A (IC50 = 2.2µM), CDK2/cyclin E (IC50 = 7.5µM), CDK4/cyclin D1 (IC50 = 12µM), CDK5/p35 (IC50 = 5.5µM)) and of GSK-3β (IC50 = 600nM). Studies investigating functional isoindigos show that they have the ability to disrupt cell growth and proliferation. The compound is a potent aryl hydrocarbon receptor ligand and is found in human urine and fetal bovine serum. Synthesized isoindigo-based oligothiophenes are used to study heterojunction solar cells. Shown to inhibit allergic contact dermatitis by regulating T helper mediated immune system in a DNCB-induced model.