Abstract
ABSTRACTA series of star‐shaped oligofluorene molecules, each containing a TPE core, have been specifically designed and produced to show effective aggregation‐induced emission (AIE). Each molecule differs either in the number of fluorene units within the arms (e.g., 1 or 4, compounds 4 and 5), or the terminal group positioned at the end of each arm (e.g., H, TMS, or TPA, compounds 4, 6, and 7). Although they are all poor emitters in solution phase they become efficient yellow‐green luminogens in the condensed state. Their AIE properties were investigated in THF/H2O mixtures, with each molecule exhibiting a clear emission enhancement at specific water contents. An all‐organic distributed feedback (DFB) laser was fabricated using compound 4 as the gain material and exhibited an average threshold energy fluence of 60 ± 6 μJ/cm2 and emission in the green region. Furthermore, piezofluorochromism studies on a thin film of this material displayed a linear dependence of the amplified spontaneous emission (ASE) peak position on applied pressure, indicating potential applications as lasing‐based pressure sensors. © 2016 The Authors. Journal of Polymer Science Part A: Polymer Chemistry Published by Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 734–746
Highlights
Many light-emitting materials present efficient fluorescence in dilute solutions, while more concentrated solutions, or solid-state samples, exhibit no emission. This is due to aggregation of chromophores via p–p stacking leading to formation of species that undergo decay via nonradiative pathways,[1] commonly described as aggregation-caused quenching (ACQ)
Such an issue can be detrimental for application of organic materials in a series of optoelectronic and photonic devices such as organic light-emitting diodes (OLED), lasers, and down-converters, where the emissive layer is in the solid state
Among the whole series the highest Stokes shift of 182 nm was observed for compound 4. Their aggregation-induced emission (AIE) properties were investigated in water:THF mixtures in which compound 4 showed emission enhancement after the addition of 50% of water to the mixture, being maximized with 80% water content
Summary
Many light-emitting materials present efficient fluorescence in dilute solutions, while more concentrated solutions, or solid-state samples, exhibit no emission. A benzene-cored star-shaped material with pendant TPE arms exhibited AIE with a morphological change in the aggregates formed upon addition of water.[22] At low water concentrations, crystalline aggregates were formed, while at high water concentrations, the aggregates were amorphous, resulting in a bathochromic shift of the emission and a decrease in intensity.
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