Self-assembled small molecule spherulites under mild conditions: High solid-state quantum yield and unique interconnected structural and fluorescent colors

Spherulites are generally fabricated from cooling polymer melts, while their fabrication under mild conditions or from small molecule materials has been barely reported. Besides, organic luminescent molecules typically suffer from low quantum yields in a solid state. Moreover, preparing material with interconnected and simultaneous changes in structural and fluorescent colors is challenging. Here, we present the first solution-derived spherulites with unique interconnected structural and fluorescent colors, self-assembled from stearoylated monosaccharides at room temperature. D-galactose stearoyl ester self-assembled into banded spherulites, containing twisted nanoplates and interconnected simultaneously changing structural and fluorescent colors. In comparison, D-mannose stearoyl ester can only form non-banded spherulites, which contain oriented nanoplates and uniform structural and fluorescent colors. Such materials revealed a novel negative correlation between fluorescence and birefringence, termed alignment-promoted quenching propensity. Remarkably, the solid-state fluorescence quantum yields of galactose and mannose-derived spherulites are as high as 49 ± 2% and 51 ± 2% respectively, approximately ten times higher than those of unmodified monosaccharides. These quantum yield values are among the highest of reported organic nonconventional fluorophores and even comparable to those of conventional aromatic chromophores. Moreover, these spherulites manifested an unexpected excitation-dependent multicolor photoluminescence with a broad-spectrum emission (410−620 nm). They show multiple peaks in the photoluminescent emission spectra and broad fluorescence lifetime distributions, which should be attributed to the clustering of a variety of oxygen-containing functional groups as emissive moieties.