Visible–Near-Infrared Range Whispering Gallery Resonance from Photonic μ-Sphere Cavities Self-Assembled from a Blend of Polystyrene and Poly[4,7-bis(3-octylthiophene-2-yl)benzothiadiazole-co-2,6-bis(pyrazolyl)pyridine] Coordinated to Tb(acac)₃

A novel red emitting copolymer (P1) was prepared (Mn ∼ 10.7 kDa) by copolymerizing tridentate ligand, namely 2,6-bis(pyrazolyl)pyridine (BPP) with 4,7-bis(2-ethynyl-5-thienyl)-2,1,3-benzothiadiazole. This copolymer readily formed an orange yellow emitting metal containing conjugated polymer (P1.Tb) with Tb(acac)3. Further, a judicial blend of P1.Tb with polystyrene and its subsequent self-assembly in THF/water produced microspheres with smooth surface area. Interestingly, continuous wave laser excitation of a single microsphere displayed whispering-gallery-mode (WGM) resonance modes over a broad wavelength range covering visible (Vis) and near-infrared (NIR) regions (0.550-0.875 μm). The estimated Q factor was up to 700, which is very high for a metal containing conjugated polymer (MCCP)-based optical gain medium.