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

Abstract

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.

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

“…On the other hand, from toluene, CHCl 3 , and cyclohexane, a solvated colorless crystal without π‐stacking interactions is alternatively obtained (crystal b ) [54] . In this work, we will discuss only crystal a , whose crystal structure was determined by powder X‐ray diffraction analysis using the Rietveld method in our previous work [55] . In addition, to collect deep information on the structure–property relationship, the series of compounds were prepared by introducing o ‐carborane to the 1‐position of anthracene ( 1‐H ) and 1,4‐positions ( 14‐H ).…”

“…Previously, we reported thermochromic and mechanochromic luminescent properties of bis‐ o ‐carborane‐modified anthracene ( 18‐H , Scheme 1). [54,55] From the spectroscopic and crystallographic analyses, it was shown that these multiple luminochromic properties should be commonly originated from the π‐stacking crystal structure. Thermochromic luminescence was attributed to the elongation and shortening of π–π distance, [54] and mechanochromic luminescence was induced by the destruction and construction of the π‐stacking structure [55] …”

Near-infrared aggregation-induced emission characteristics of new o-carborane fluorophores with large stokes shifts and self-recovering mechanochromic luminescence

“…The former emission band is attributed to the LE state emission localized at the PXZ and PTZ derivatives, while the latter belongs to the ICT state emission. 30,34 Moreover, we measured the emission spectra at a low temperature of 77 K in 2-MeTHF (Fig. 2).…”

Solid-state excimer emission ofo-carborane derivatives and applications for stimuli-responsive luminescent materials

“…6). 35 In the case of 13 , the bathochromic emission band was observed after grinding; meanwhile the hypsochromic emission band appeared from 14 . Moreover, self-recovery of the luminescent color proceeded in 13 at room temperature but in 14 it proceeded at 323 K. In the bis- o -carborane systems, similar to a previous report in which an excimer was not mentioned, 36 the self-recovering behaviors from the ground color to the pristine color were observed after the mechanical treatments.…”