Reversible Vapochromic Luminescence Accompanied by Planar Half‐Chair Conformational Change of a Propeller‐Shaped Boron β‐Diketiminate Complex

• Published in: Chemistry : a European journal Vol. 27; no. 36; pp. 9302 - 9312
• Main Authors: Ito, Shunichiro, Yaegashi, Misao, Tanaka, Kazuo, Chujo, Yoshiki
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 25.06.2021
• Subjects: Boron; boron complexes; Chemistry; Climate change; Color; crystal transition; Crystallization; crystallization-induced emission; Crystals; Exposure; Fluorescence; Global warming; Leakage; Organic compounds; Phases; Time constant; vapochromism; Vapors; VOCs; Volatile organic compounds; Crystal Transition; Crystallization-Induced Emission; Vapochromism; fluorescence; Boron Complex
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.202101107

Leakage of volatile organic compounds (VOCs) is one of the most severe industrial problems, because it can cause environmental pollution, global warming, fire, and explosion. Hence, the visualization of leakage is an essential technology to detect it at an early stage. Molecular crystals, fluorescence color of which can be changed by the exposure to VOCs could potentially serve as the sensing materials for realizing rapid and facile VOC detection. However, these materials usually require harsh conditions, such as heating or a vacuum, to recover their initial phases for reuse. Therefore, it remains a challenge to obtain completely reversible sensing systems without such energy‐consuming recycling processes. Herein, the reversible color change of fluorescence from the crystals of a propeller‐shaped boron β‐diketiminate complex is reported. The complex was crystallized in distinct crystalline phases having different luminescent colors. Importantly, these phases were interconverted very rapidly (time constant <60 s) and repeatedly upon exposure to the vapors of the appropriate VOCs. The small energy differences between conformers of the complex could lead to this pseudopolymorphic behavior. This finding could be applied for the development of further eco‐friendly reversible sensing materials based on four‐coordinated boron complexes. A propeller‐shaped boron β‐diketiminate complex exhibits a reversible color change of fluorescence originating from pseudopolymorphism. The emission color rapidly changes from green to blue when its pure crystals are exposed to an appropriate group of volatile organic compounds and vice versa. Such luminescent color changes are derived from crystal–crystal transitions accompanied by the planar‐to‐half‐chair conformational changes of the complex. The small energy differences between the conformers of the complex can afford this pseudopolymorphic behavior.