Yumei Zhao

Stacking-induced broadband near-infrared absorption beyond 2500 nm and deep-red phosphorescence from purely organic radicals

Herein, we present two new purely organic radicals which exhibit unusual stacking-induced broadband near-infrared (NIR) absorption beyond 2500 nm and deep-red phosphorescence. These interesting properties make them promising light harvesting and solid-state NIR phosphorescent materials.

Morphology-controllable fabrication of organic microcrystals by solid-phase reactions: revealing morphology-sensitive highly efficient phosphorescence and enhanced near-infrared absorption

The vapor-solid and solid-phase anion exchange reactions provide useful strategies for the morphology-controllable fabrication of organic microcrystals. The changes in morphology induce interesting changes in the photophysical properties of organic microcrystals. Significantly, hexangular microflakes exhibit higher phosphorescence quantum yield (up to 57.5%) and enhanced near-infrared absorption.

Positional isomerism in triarylmethyl carbocation radical salts: positional isomeric effects, crystal structures and properties

Through a simple and mild approach, we unprecedentedly synthesized three novel triarylmethyl carbocation radical salts, namely bisimidazo[1,2-a]pyridin-2-one-yl(2-pyridyl)methyl carbocation radical salt (1), bisimidazo[1,2-a]pyridin-2-one-yl(3-pyridyl)methyl carbocation radical salt (2), and bisimidazo[1,2-a]pyridin-2-one-yl(4-pyridyl)methyl carbocation radical salt (3). Single-crystal X-ray diffraction analyses reveal that 1, 2 and 3 are positional isomers with different one-dimensional (1D) chain structures. Through supramolecular interactions, the 1D chains of 1 are further assembled into a 1D double-stranded chain, then into a two-dimensional (2D) layer structure, and the 1D chains of 2 and 3 are also assembled into 2D layer structures. This work indicates that the positional isomeric effects of pyridyl groups in the three carbocation radical salts are significant in the construction of isomers, because 1, 2 and 3 were synthesized and crystallized under the same conditions. Furthermore, these positional isomers exhibit different magnetic susceptibility values at 300 K. 1 with 1D double-stranded chains consists of one repetitive unit having four carbocation radical moieties, giving a magnetic susceptibility value of 1.636 emu K Oe−1 mol−1 at 300 K. 2 with 1D chains consists of one repetitive unit with two carbocation radical moieties, giving a magnetic susceptibility value of 0.747 emu K Oe−1 mol−1 at 300 K. 3 exhibits a magnetic susceptibility value of 0.326 emu K Oe−1 mol−1 for one isolated spin of the carbocation radical. Compared with 2 and 3, 1 shows broad and stronger NIR absorption bands from 800 nm to 1951 nm, probably ascribed to its 1D double-stranded chain structure, antiparallel arrangements of 2-pyridinium rings in the 1D chains, and/or tetra-connecting hydrogen-bonding bridge.

Stimuli-responsive switching of magnetic properties and solid-state colors for 2,3′-biimidazo[1,2-a]pyridin-2′-one radical derivatives

The reversible switching of properties for organic materials is an attractive field for both fundamental research and practical application. We report herein a novel class of organic radicals, which exhibits the reversible magnetic behavior or color switching in response to acid–base stimuli. The reversibly switchable behaviors are ascribed to the proton-triggered molecular structure and conformation conversions. The responsive dynamic magnetic properties are unique in terms of the acid–base vapor stimuli. The present work provides new access to develop dynamic multifunctional materials which can be reversibly switched between different colors or magnetic behaviors based on external stimuli.

Phosphorescence, near-infrared absorption and nonlinear optical property of a new chiral organic crystal

A new enantiomerically pure compound was synthesized by the single step reduced reaction from 2-(imidazo[1,2-a]pyridin-2-yl)-2-oxo-N-(pyridin-2-yl)acetamide via chiral induction with D-tartaric acid in good yield. Single crystal data confirm this compound crystallizes in chiral space group P21. Transmission spectrum reveals that the crystal has low UV cut-off of 372 nm and has a good transmittance in the entire visible and near-infrared (NIR)region to 1100 nm, indicating its optical application. Kurtz powder test shows a good second harmonic generation (SHG) which also demonstrates its chiral structure. Moreover, this material exhibits blue phosphorescence with quantum yield of 3.6% and unusually NIR absorption between 1500 nm and 2500 nm. Therefore, this new chiral crystal is a promising multifunctional material for the blue phosphorescence, NIR absorption and nonlinear optical (NLO) applications.