Slight substituent modification in coumarin molecular structures for strong solid emission and application in light-emitting devices

Abstract

Molecular engineering of organic luminophores with slightly twisted molecular conformations for efficient emitting in a solid state is highly challenging but required for light-emitting devices. In this contribution, two series of coumarin derivatives, namely, α-NCMs and β-NCMs, which slightly differ in their substituents at the 3-position of the molecular skeleton are demonstrated. The fluorescent quantum yield in solid state increased by up to 92.6% by replacing the α-naphthalene ring (α-NCMs) substituents to β-naphthalene (β-NCMs) ring at the 3-position. Meanwhile, fluorescent colors are successfully tuned by introducing substituents with various electronic properties at the 7-position of the molecular skeleton. Density functional theory and single-crystal analysis reveale that the isomeric naphthalene ring at the 3-position significantly influenced the molecular conformations, molecular-packing models, and intermolecular interactions. All light-emitting devices with β-NCMs as the phosphors yield higher luminescence than their counterpart α-NCMs-based devices. Among these devices, those with β-NCM2 having a N, N-diethylamino group substitute at the 7-position provide an impressive maximum luminance of 54 030 cd/m2 at a work voltage of 3.8 V.