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

Abstract

Herein, we report 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 the characteristic crystal structure 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 exhibit the photosalient effect accompanied with 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 formation of those species was facilitated by the π‐stacking structure of anthracene units. Moreover, we found unusual temperature dependency of the occurrence of the photosalient effect. According to the data from variable temperature X‐ray crystallography, the strong correlation between lattice shrinkage and strain accumulation is suggested.

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

“…Based on anthracene analogs, we aimed to clarify the structural factors which are required for the excimer formation. 42 As a result, we found that two structural features are essential. The first is that aromatic ring moieties need to stack and form a columnar structure.…”

“…In particular, it has recently been discovered that an o -carborane-modified anthracene derivative exhibits photo-triggered dimerization and a subsequent photosalient effect. 42 In this section, the mechanism is described.…”

“…8b). 42 It was found that 13 and 15 form the characteristic crystal structure involving the columnar π-stacking structures of the anthracene units. In particular, it was shown that these crystals can exhibit the photosalient effect accompanied by photochemical [4 + 4] cycloaddition and temperature-dependent photophysical dual-emission properties including excimer emission of anthracene.…”

Disproportionation Thermochromic Response in a Luminescent Lanthanide Metal–Organic Framework

“…Stimuli-responsive luminescent materials show high prospects for applications in sensing and information security on account of the diverse and reversible changes in emission signals, such as intensity, − color, − and lifetime, , in correlation with environmental parameters. A variety of methods, including light, − mechanical force, , temperature, − water, , electricity, and chemicals, , have been used as the stimulation sources. As a basic physical parameter, temperature is one of the most common stimuli due to its accessibility, controllable range, and diverse application scenarios.…”

Influence of Intermolecular Structural Effects on Radiative Efficiency in Xanthene-Based Carboranyl Luminophores

“…38−45 For example, a geometry restricting the rotation of the aromatic group relative to the carborane cage in an ocarboranyl compound with a dimethylfluorene D group was shown to not only promote high-efficiency ICT-based emission but also enhance thermally activated delayed fluorescence. 34 Furthermore, compounds featuring o-carborane units linked to various π-aromatic fluorescent donors, such as naphthyl, 36,46,47 anthracenyl, 30,35,39,43,44,48 tetraphenylethenyl, 49,50 pyrenyl, 14,40,42 chrysenyl, 51 and indolocarbazole 52,53 moieties, can exhibit multiple photoluminescence and specific emissive features (e.g., mechanochromism, thermochromism, photosalient effect, etc.) in the TICT state.…”