Studies of the Optical and Sensing Properties of 1,3,5-Triazine-Cored Star-Shaped (D-π)3-A Molecules with Various Amino-Donor-Type Cation Receptors

Abstract

Abstract We newly designed and synthesized two kinds of 1,3,5-triazine-cored star-shaped (D-π)3-A molecules with 1-aza 15-crown 5-ether receptors (TSM-ACE) and dipicolylamino receptors (TSM-DPA), which possess an intramolecular charge transfer (ICT) nature and exhibit ICT-based optical properties (ICT transition absorption and fluorescence from a ICT excited state). Both TSM-ACE and TSM-DPA display proton-induced optical spectral blue-shifts followed by red-shifts depending on their inherent two-step protonation behavior. Furthermore, TSM-ACE displays optical spectral blue-shifts followed by red-shifts upon stepwise complexation of Mg2+, whereas TSM-DPA displays optical spectral blue-shifts upon the complexation of Zn2+. The cation sensing mechanism can be explained as follows: (i) the initial blue shift is caused by the decreased ICT donor abilities of three amino-donor-type receptors (a decrease of the ICT efficiency) upon binding cations, and (ii) the second red shift is caused by an increased acceptor ability of the 1,3,5-triazine core upon binding cations. Consequently, we revealed that TSM-ACE and TSM-DPA with different cation-recognition functionalities serve as a unique optical sensor capable of visual and distinct detection of not only protons but also different kinds of metal ions.