Ionic Organic Microcrystals with Bright Deep-Blue Luminescence and Acid/Base Vapor Response

Abstract

A new class of high-quality ionic organic microcrystals with bright deep-blue luminescence (with up to 60% quantum yield) have been prepared in situ by the protonation of 2,2′-di­(pyrid-2-yl)­biphenyl (1) with different proton acids (HCl, HClO4, CH3SO3H, or CF3SO3H). The obtained rod-shaped microcrystals are characterized by SEM and PXRD analyses. As a result of the deprotonation and reprotonation of the pyridine groups, the microcrystals of 1(HCl)2 show reversible blue luminescence switching in response to NEt3/HCl vapor. In addition, single crystals of the ionic salts of 1(HCl)2, 1(HClO4)2, 1(CH3SO3H)2, and 1(CF3SO3H)2 have been obtained. X-ray analyses show that the counteranions are connected to the pyridinium protons by hydrogen bonding.

Full‐Color and White Circularly Polarized Luminescence of Hydrogen‐Bonded Ionic Organic Microcrystals

“…The crystals of 1 – 7 are circular dichroism (CD) and CPL silent (Figure S3). Upon the addition of (−)‐CSA, the absorptions of 1 – 7 in THF solutions showed the generation of a new charge transfer (CT) absorption band due to the protonation of the pyridine units (Figure S4) [13–15] . In the meantime, the short congeners 1 – 3 display red‐shifted and enhanced CT emissions, while the longer congeners 4 – 7 exhibit red‐shifted but decreased emissions upon protonation.…”

Reversible on/off conformational switching of pentafluorobenzoyl amide triggered by acid vapor and sublimation

“…Herein, we describe an on/off-type amide conformational transformation in the crystalline state induced by HCl vapor in one direction and by sublimation with pumping to remove HCl in the other direction. Although some acid-responsive crystals have been reported, [13][14][15][16][17] most involve stacking changes or subtle geometry changes, rather than a drastic change of the stable conformation such as conversion between E and Z conformations. Thus, the fact that our molecular switch 3 (Fig.…”

Selective, Anisotropic, or Consistent Polarized‐Photon Out‐Coupling of 2D Organic Microcrystals

“…Upon the addition of HClO 4 to the solutions of 1-5, lower-energy intramolecular charge transfer (CT) absorptions and emissions from the substituted phenyl group to the pyridinium group appeared as a result of the protonation of the pyridine unit (Figure S3). [13,14] Using the in situ protonation and nanoprecipitation method, [13] high-quality 2D microplates were obtained by adding excessive aq HClO 4 (72 %) to the solution of 1-5 (4-40 mM) under ultrasonication (see details in Supporting Information). NMR, mass spectra, and elemental analyses all indicate that the obtained microcrystals are quantitatively protonated by HClO 4 .…”