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

Fan-Yi Meng; Yen-Hao Hsu; Zhiyun Zhang; Pei-Jhen Wu; Yi-Ting Chen; Yi-An Chen; Chi-Lin Chen; Chi-Min Chao; Kuan-Miao Liu; Pi-Tai Chou

doi:10.1002/asia.201701057

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

Chem Asian J. 2017 Dec 5;12(23):3010-3015. doi: 10.1002/asia.201701057. Epub 2017 Oct 30.

Authors

Affiliations

¹ Department of Chemistry, National Taiwan University, Taipei, 10617, Taiwan, R.O.C.
² Department of Medical Applied Chemistry, Department of Medical Education, Chung Shan Medical University, Taichung, 40201, Taiwan, R.O.C.

PMID: 28980416
DOI: 10.1002/asia.201701057

Abstract

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.

Keywords: eight-membered rings; fluorescence; hydrogen bonds; proton transfer; single crystals.