Highly Efficient and Thermally Durable Luminescence of 1D Eu3+ Coordination Polymers with Arsenic Bridging Ligands.

In this work, bisarsine oxides were evaluated as novel bridging ligands, aiming to develop practical and efficient luminescent lanthanide coordination polymers. We have synthesized one-dimensional (1D) Eu3+ coordination polymers that incorporate bisarsine oxide bridging ligands and hexafluoroacetylacetonate anions. These polymers exhibited a denser packing of chains compared to analogous polymers bridged with bisphosphine oxides. The coordination polymers demonstrated exceptional thermal stability and substantial emission quantum yields. Additionally, the bisarsine oxides induced a pronounced polarization effect, facilitating a sensitive electric dipole transition that yields considerably narrow band red emission. Remarkably, the Eu3+ coordination polymers with bisarsine oxides maintained intense emission even at 550 K. A distinctive feature of these polymers is their heating-induced emission enhancement observed when the temperature was increased from 300 K to 400 K.

The Photosalient Effect and Thermochromic Luminescence Based on o-Carborane-Assisted π-Stacking in the Crystalline State.

Herein, we report the unique multiple-stimuli responsiveness of anthracene-tethered o-carborane derivatives. We designed and synthesized anthracene derivatives with different substitution positions and numbers of the o-carborane units. Two compounds had characteristic crystal structures involving the columnar π-stacking structures of the anthracene units. From the analysis of crystalline-state structure-property relationships, it was revealed that the crystals exhibited the photosalient effect accompanied by photochemical [4+4] cycloaddition reactions and temperature-dependent photophysical dual-emission properties including excimer emission of anthracene. Those properties were considered as non-radiative and radiative deactivation pathways through the excimer formation in the excited state and the formation of excimer species was facilitated by the π-stacking structure of anthracene units. Moreover, we found unusual temperature dependency on the occurrence of the photosalient effect. According to the data from variable temperature X-ray crystallography, a strong correlation between lattice shrinkage and strain accumulation is suggested.

Direction Switching and Self-Recovering Mechanochromic Luminescence of Anthracene-Modified o-Carboranes.

Luminochromic behaviors regarding mechanochromic luminescence (MCL) of o-carborane-modified anthracene derivatives are reported. We have previously synthesized bis-o-carborane-substituted anthracene and found that its crystal polymorphs show dual-emission properties composed of excimer and charge transfer (CT) emission bands in the solid state. Initially, we observed the bathochromic MCL behavior from 1 a originating from emission mechanism alteration from dual emission to CT emission. By inserting the ethynylene spacers between anthracene and o-carboranes, compound 2 was obtained. Interestingly, 2 showed hypsochromic MCL originating from the emission mechanism alteration from CT to excimer emission. Furthermore, luminescent color of ground 1 a can be recovered to the initial state by allowing to stand at room temperature, meaning that self-recovery proceeds. Detailed analyses are described in this study.

Controlling the Dual-Emission Character of Aryl-Modified o-Carboranes by Intramolecular CH⋠⋠⋠O Interaction Sites.

Invited for the cover of this issue is the group of Kazuo Tanaka at Kyoto University. The image depicts the control of solid-state dual-emissive properties by modulating the intramolecular hydrogen bonding in boron clusters. Read the full text of the article at 10.1002/chem.202200155.

Controlling the Dual-Emission Character of Aryl-Modified o-Carboranes by Intramolecular CH⋠⋠⋠O Interaction Sites.

It is still challenging to realize a dual-emission system, in which two luminescent bands simultaneously appear by photoexcitation, in solid with organic dyes due to the difficulty in regulation of electronic properties in the excited state and concentration quenching. o-Carborane is known to be a versatile platform for constructing solid-state emitters since the sphere boron cluster is favorable for suppressing intermolecular interactions and subsequently concentration quenching. Here, we show solid-state dual-emissive o-carborane derivatives. We prepared 4 types of o-carborane derivatives and found dual-emission behaviors both in solution and solid states. By regulating the rotation at the o-carborane unit with the intramolecular Ccage H⋅⋅⋅O interaction, the dual-emission intensity ratios were changed. Finally, it was demonstrated that the overall photoluminescence spectra can be estimated using the binding energy of intramolecular interactions.