Fluorescent Crystals of Zwitterionic Imidazolium Pyridinolates: A Rational Design for Solid‐State Emission Based on the Twisting Control of Proemissive N‐Aryl Imidazolium Platforms

Abstract

The synthesis and structural variations in solid‐state emission of zwitterionic imidazolium pyridinolates are described. N‐Alkylimidazolium 2‐pyridin‐3‐olate 1 exhibits intense blue emission at ambient temperature (Φ298 K = 0.44, λmax = 424 nm) in the crystalline state, while phenolate 2, another pyridinolate analogue bearing the nitrogen atom at a different position on the pyridine ring 3, and N‐phenylimidazolium ring 4 are less emissive (Φ298 K = 0.05, 0.05, and 0.04) under the same measurement conditions. Temperature‐dependent emission spectra indicate that crystal 1 exhibits high heat‐resistance properties towards emission decay and redshifting thermochromism upon increasing temperature, both of which are in contrast with the heat quenching and blueshift properties of phenolate analogue crystal 2 under the same measurement conditions. XRD analysis and DFT calculations revealed that the effect of the 2‐pyridinolate functionality on the specific efficiency and thermochromism in the crystalline‐state fluorescence of imidazolium arenolates arises from specific restriction of molecular rotation and the resultant molecular constraints in the crystals.

Facile synthesis, aggregation-induced emission, mechano- and thermochromism of o-carborane–tetraphenylethene dyads with a short CH(OH) linker

“…[59][60][61][62] Most organic luminescent materials have disadvantages in this respect such as reduction in luminescence intensity and widening of the emission peak at high temperature, to some extent. [63][64][65] Therefore, it is necessary to study the thermofluorochromic properties of organic luminescent materials. The emissions of the solid compounds were studied, in the range of r.t. to 160 1C.…”