Remarkable solution and solid-state color-tunable luminescence of diethylamino-coumarin derivatives and application in warm-white LEDs

Abstract

Organic materials with solution and solid dual efficient, color-tunable luminescence are potentially useful for sensors and optical devices. Herein, a series of donor-π-acceptor luminophores, named BMs, with different phenyl substituents at the 3-positions of 7-diethylamino-coumarin was developed. All four compounds with slightly twisted structure rendering BMs have bright emission in solution and solid state. BMs not only possess solvatochromic properties in solution but also realize color tuning from cyan (480 nm) to deep red (661 nm) in solid states. Among them, the fluorescence quantum yield of compound BM1 in solid state reached 98.2%, and the fluorescence quantum yield in solution was 77.1%. Time dependent density functional theory calculation and single crystal analysis show that with the increase in the electron-withdrawing ability of 4-phenyl moiety at the 3-position of coumarin, the charge transfer effect was strengthened gradually, and the photoluminescence mechanism changed from intramolecular charge transfer (ICT) to twisted ICT on account of the electron acceptor changed accordingly. Moreover, the cyan phosphor BM1 and the deep-red phosphor BM4 were laminated to fabricate an impressive warm-white light-emitting diode device with a maximum brightness of 52,090 cd/m2 at an operating voltage of 4.0 V.