A transition metal-free and efficient synthesis of fused azapolycycles via a multicomponent reaction has been developed using mucohalic acid as a C₃ synthon. The reaction promoted by the simple inorganic base K₂CO₃ gives serial C₁-functionalized benzo[4,5]imidazo[1,2-a]pyridine products using symmetrical and unsymmetrical substrates with satisfactory yields. What is more, the target compound 4a as a representative example exhibits the aggregation-induced emission (AIE) property, and its AIE performance can be applied to effectively sense picric acid (PA) with a detection limit and quenching constant of 1.15 × 10^–7 M and 3.39 × 10⁴ M⁻¹, respectively.