A sp2-carbon-linked orange-emitting 2D covalent organic framework containing pyrene and tetraphenylethene units: Synthesis and application for rare-earth free white light-emitting diodes

Abstract

A sp2-carbon-linked 2D covalent organic framework (COF) containing pyrene and tetraphenylethene units was synthesized via Knoevenagel condensation by using 4,4′,4″,4‴-(ethene-1,1,2,2-tetrayl)tetrabenzaldehyde (ETTBA) and 2,2′-(pyrene-1,6-diylbis(4,1-phenylene))diacetonitrile (PDPD) as monomers. This COF consisted of a periodic single-pore rhombic (R) structure and was in an eclipsed stacking mode (AA-R). Its powders emitted bright orange light which was mainly located at 555∼750 nm with the maximum emission wavelength (λem,max) of 612 nm, and its photoluminescence quantum yield (PLQY) was 21.0 %. The COF showed high thermal stability, its thermal decomposition temperature (Td) was up to 509 °C, and its relative emission intensity at 90 °C remained 93.1 % of that at 30 °C, at 150 °C was 70.4 % of that at 30 °C, which suggested it was suitable for LEDs. The COF together with a quasi-green-emitting graphitic C3N4 derivative (s-g-C3N4-Ph) as rare-earth free phosphors under the excitation of GaN-based blue light chips (around 460 nm, 25.0 lm·W−1), a series of cold/neutral/warm white LEDs with good light quality were successfully fabricated. For example, one of white LEDs showed high color rendering index (CRI) of 83.1, its correlated color temperature (CCT) was 6384 K, luminous efficacy (LE) was 19.19 lm·W−1, moreover, its CIE chromaticity coordinates (0.32, 0.32) was very close to (0.33, 0.33) of pure white light.