Effect of small flanking donor group on mechanofluorochromism and enhanced emission: A comparative study between ester and acid linked solid state emitters Madhuparna Chakraborty Birla Institute of Technology and Science-Pilani, India
Mechanofluorochromic small organic molecules bring immense attention to the scientific community due to their wide range of applications and academic interest. 1-2 New Strategic design of mechanofluorochromic (MFC) and mechanical force-induced enhanced emission (MIEE) active materials, governed by twisted molecular conformation and various intermolecular interactions, are highly preferred due to their unpredictability. In this context, herein we present a facile synthesis of monoacid and ester linked small unsymmetrical π-conjugates by varying the flanking donor substituents. Alteration in H-bonding and molecular packing style directs the MFC and MIEE behavior of acid and ester analogs, respectively, as observed in the tiny thiophene flanked emitters. Hence, acid analogs are MFC active but not the ester one. However, the variation in MFC/MIEE feature by tuning the donor substituent from thiophene to dimethoxybenzene has been observed for the first time. Single-crystal X-ray structures revealed the diversity in intermolecular interactions and molecular packing. The observed fact is further supported by determining the non-covalent interactions and void space using Hirshfeld surface analysis, powder X-ray diffraction, lifetime measurement, and differential scanning calorimetry (DSC) studies. Thus, flanking donor-dependent MFC and MIEE active acid and ester analogs are found to be a promising candidate for reusable security writings. References 1. J. Zhao, Z. Chi, Y. Zhang, Z. Mao, Z. Yang, E. Ubba and Z. Chi. J. Mater. Chem. C , 2018, 6 , 6327-6353. 2. H. Liu, Y. Gu, Y. Dai, K. Wang, S. Zhang, G. Chen, B. Zou and B. Yang, J. Am. Chem. Soc. , 2020, 142, 1153 - 1158.
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