Syntheses and photophysical properties of natural dehydroabietic acid-based ligands and their zinc complexes

• Published in: Journal of molecular structure Vol. 1229; p. 129793
• Main Authors: Cai, Xu-Min, Mu, Tianqi, Lin, Yuting, Zhang, Xuedan, Tang, Zhenguo, Huang, Shenlin
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 05.04.2021
• Subjects: Dehydroabietic acid; Fluorescence; Molecular Motion; Solvatochromism; Fluorescence; Solvatochromism; Molecular Motion; Dehydroabietic acid
• ISSN: 0022-2860; 1872-8014
• DOI: 10.1016/j.molstruc.2020.129793

•An easily obtained derivative 1 from natural dehydroabietic acid was applied as a precursor in this work, which could further derivatize to its Schiff base ligands and corresponding zinc complexes with a high crystalline yield.•The larger dihedral angles of the ligands are indicative of strong molecular motion, resulting in their luminescence quenching.•When the ligands were structurally restricted via coordination to zinc ion, their fluorescence occurred, most probably due to the restriction of intramolecular motion.•This work not only discusses the relationship between their photophysical properties and molecular structures, but also provides a new natural resource for further research in fluorescent materials. Two Schiff base ligands (2a and 2b) and their zinc complexes (3a and 3b) have been designed and facilely synthesized through simple condensation reactions using compound 1 derived from natural dehydroabietic acid as the precursor. The larger dihedral angles of the ligands shown by the single crystal X-ray diffraction analysis indicate their stronger molecular motion, which is in consistence with their low fluorescence efficiency that is verified by the photophysical measurements. After coordination with zinc ions, the fluorescence intensity of the zinc complexes is larger, which might be explained by the structural rigidification via coordination, thereby reducing the energy loss from molecular motion. Furthermore, complex 3b exhibits a specific negative solvatochromic effect, and the absorption of its maximum wavelength shows a hypsochromic shift with increased polarity. Such solvatochromic phenomena can be explained by the synergy of intramolecular charge transfer and the proximity effect that may increase the energy difference between the ground state and the excited state in polar solvents. This work not only discusses their relationship between photophysical properties and structures, but also provides a new natural source for further research in fluorescent materials. [Display omitted]