Research Digest 15structures Pyrene-derived carboxamide with alkylsilyl and tert-butyl groups were prepared, and all compounds exhibited similar purple-to-blue bathochromic MCL upon grinding (Figure 2, black and blue lines). However, the spontaneous fluorescence recovery rates were significantly different, despite their slight differences in the chemical components and molecular packing motifs. Single-crystal XRD experiments and Hirshfeld and energy framework analyses indicated that the chromic direction was dictated by the packing motif, while fluorescence recovery was not simply influenced by the steric hinderance but by the Fig. 1. A schematic of MCLand distribution of intermolecular interaction network patterns (Figure 2, right). Statistic nanomechanical testing also revealed the reversibility of deformation after unloading, and the dynamic responses of molecular solids were demonstrated by temperature-dependent spectroscopy, crystallography and FT-IR measure-ments either in crystalline or ground/annealed samples. These correlations were established by independent variables obtained from spectroscopy, crystallography, and nanomechanics.The outcomes of our study contribute to a broader and deeper understanding of the MCL behaviour, including spontaneous fluorescence recovery processes, and inspire further exploration of innovative materials and devices based on simple organic systems.Fig. 2. MCL profiles (black: pristine, blue: ground, red: 30 min at RT after grinding, green: 30 min at RT and 30 min heating at 50˚C after grinding) and the determinant factors of chromic directions and self recovery kinetics.References 1) Y. Sagara, T. Kato, Nat. Chem. 2009, 1, 605-610. 2) K. Muthamma, D. Sunil, P. Shetty, Mater. Today Chem. 2020, 18, 100361. 3) P. Shi, D. Deng, C. He, L. Ji, Y. Duan, T. Han, B. Suo, W. Zou, Dye. Pigment. 2020, 173, 107884. 4) Y. Sagara, H. Traeger, J. Li, Y. Okado, S. Schrettl, N. Tamaoki, C. Weder, J. Am. Chem. Soc. 2021, 143, 5519. 5) H. Ito, T. Saito, N. Oshima, N. Kitamura, S. Ishizaka, Y. Hinatsu, M. Wakeshima, M. Kato, K. Tsuge, M. Sawamura, J. Am. Chem. Soc. 2008, 130, 10044. 6) G. R. Krishna, M. S. R. N. Kiran, C. L. Fraser, U. Ramamurty, C. M. Reddy, Adv. Funct. Mater. 2013, 23, 1422. 7) A. Wrona-Piotrowicz, M. Ciechańska, J. Zakrzewski, R. Métivier, A. Brosseau, A. Makal, Dye. Pigment. 2016, 125, 331.integrating Solid-state Recovery of Organic MechanophoresYuichi HIRAI1. Outline of ResearchMechanochromic luminescence (MCL), the phenomenon where organic and coordination compounds exhibit reversible changes in their emission intensity and/or wavelength under mechanical stimuli, has emerged as a captivating area of research in materials science, chemistry, and photonics.1) It has garnered considerable attention owing to its potential applications in sensors to visualize the location/magnitude of the stress and information encryption systems for anticounterfeiting technologies.2,3)MCL is driven by reversible breaking and formation of non-covalent interactions, such as π–π stacking, hydrogen bonding, or metallophilic interactions, which play a crucial role in the molecular packing and electronic communication within the material.4,5) Thus, understanding the fundamental principles governing MCL and elucidating structure–property relationships are necessary for designing and optimising materials with tailored MCL behaviour. However, there have been rare comprehensive demonstrations of the intricate interplay between molecular their dynamic mechanical/photophysical responses in a bulk solid state, including spontaneous recovery processes (Figure 1).6)In this study, we focused on a family of pyrene-derived carboxamides with alkylsilyl groups7) owing to their reported monomer-like purple fluorescence in the solid state and the characteristic “half-stacking” arrangement, which may trigger MCL by increasing or decreasing the effective π-orbitals overlaps. We investigated the fluorescence responsivity from a broad perspective using crystallography, spectroscopy, and nanomechanics to guide the design and development of novel materials with enhanced MCL properties.2. Research Activities
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