J-aggregation-induced photoluminescence in electrospun pullulan/ 2-(2-fluorophenyl)-3-hydroxy-4H-chromen-4-one composite mat for photonic applications

Abstract

The nonfluorescent pullulan matrix was fabricated via an electrospinning technique with intriguing dual emitting 2-(2-fluorophenyl)-3-hydroxy-4H-chromen-4-one as a dopant. The single crystal X-ray diffraction data of the dopant revealed the orientation of the molecules in the crystal lattice. The reduced diameter of the pullulan nanofiber from 328 nm to 32 nm upon fabrication was attributed to the improved crystallinity. The higher moisture resistance of the pullulan/dopant composite nanofiber mat was evidenced by an enhanced water contact angle from 29° to 65.9°. The pullulan/dopant composite nanofiber mat exhibited a bathochromic shift in absorption profile from 250 nm to 296 nm. The subsequent dual emission at 426 nm (Blue) and 532 nm (Green) was accompanied by the large Stoke's shift value of 90–236 nm. The redshift of the emission profile in the pullulan/dopant composite mat from 400 nm to 426 nm could be due to the J-aggregation of the dopant molecules in the pullulan matrix. The band gap of the composite nanofiber mat ranged from 2.41 to 2.91. The optimum quantum yield of 32.1–36.72% and enhanced refractive index value suggested the potential application of fabricated pullulan mat as a dual emissive layer in organic light emitting diode (OLED) material which could be an alternative option for multilayer emissive material in OLED device architecture.