Synthesis of Highly Fluorescent Thiazole Fused Benzo[a] Carbazoles by Sunlight Driven Photocyclization of Indolylthiazoles

Herein we report for the first time a sunlight‐driven, irreversible photocyclization reaction of indole‐linked trisubstituted thiazoles, for the synthesis of highly fluorescent thiazole‐fused benzo[a]carbazoles using a mixture of solvents (CH3CN: DMSO; 3 : 1). Ring opening of indole moiety was observed in the case of thiazole derivatives having 2‐methyl indole substituents. Under similar reaction conditions, photocyclization of trisubstituted thiazoles having cyclic 1,3‐dicarbonyls in place of indole moiety also worked. This reaction provides products having two medicinally important moieties thiazole and benzocarbazoles. We have studied the photophysical properties of all the products and found that most of the synthesized products have very good fluorescence quantum yields.