Crystallization-enhanced emission through hydrogen-bond interactions in blends containing hydroxyl-functionalized azine and poly(4-vinyl pyridine)

Abstract

An organic azine derivative of CN₄OH, containing both para- and ortho-hydroxyl (o- and p-OH) groups, is a fluorescent material with an emission efficiency dependent on the degree of crystallinity. With inherent hydroxyl groups, CN₄OH can be homogeneously blended with different amounts of poly(4-vinyl pyridine) (PVP) through intermolecular hydrogen-bond (H-bond) interactions. With the incorporation of one and two molar equivalents of PVP, the solid CN₄OH/PVP (4/1) and (2/1) blends emit strongly with intensity higher than pure CN₄OH. Nevertheless, a further increase of the PVP content considerably reduced the crystallinity and the emission efficiency of the blend. Initially, PVP was preferably H-bonded to the p-OHs of CN₄OH, resulting in the beneficial crystallization-enhanced emission (CEE); nevertheless, the PVP added in the later step started to bond to the o-OHs of CN₄OH, reducing the crystallinity and the CEE-related fluorescence. With appropriate H-bond interactions, the CN₄OH/PVP (2/1) blend emits with a high quantum yield (Φ_F) of 88%, in contrast to the low Φ_F of 15% for pure CN₄OH.