The Quest of Excited-State Intramolecular Proton Transfer via Eight-Membered Ring [pi]-Conjugated Hydrogen Bonding System

• Published in: Chemistry, an Asian journal Vol. 12; no. 23; p. 3010
• Main Authors: Meng, Fan-Yi, Hsu, Yen-Hao, Zhang, Zhiyun, Wu, Pei-Jhen, Chen, Yi-Ting, Chen, Yi-An, Chen, Chi-Lin, Chao, Chi-Min, Liu, Kuan-Miao, Chou, Pi-Tai
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 05.12.2017
• Subjects: Chemical bonds; Chemical synthesis; Chemistry; Computer simulation; Fluorescence; Hydrogen bonding; Protons; Upconversion
• ISSN: 1861-4728; 1861-471X
• DOI: 10.1002/asia.201701057

Searching for eight-membered ring π-conjugated hydrogen bonding (8-MR H-bonding) systems with excited-state intramolecular proton transfer (ESIPT) property is seminal and synthetically challenging. In this work, a series of π-conjugated molecules (8-HB-1, 8-HB-L1 and 8-HB-2) potentially possessing 8-MR H-bonding are strategically designed, synthesized and characterized. The configurations of these three potential molecules are checked by their X-ray structures, among which 8-HB-L1 (a structurally locked 8-HB-1 core chromophore) is proved to be an 8-MR H-bonding system, whereas 8-HB-1 and 8-HB-2 are too sterically hindered to form the 8-MR intramolecular H-bond. The ESIPT property of 8-HB-L1 is confirmed by the dual fluorescence consisting of normal and proton-transfer tautomer emissions. The insight into the ESIPT process of 8-HB-L1 is provided by femtosecond fluorescence upconversion measurements together with computational simulation. The results demonstrate for the first time a successful synthetic route to attain the 8-MR H-bonding molecule 8-HB-L1 with ESIPT property.