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

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.

Advances in the Chemistry of 2,4,6‐Tri(thiophen‐2‐yl)‐1,3,5‐triazine

“…The initial blue shift occurs due to the decreased ICT donor capacity of the amino‐donor‐type receptors on binding with cations and the second red shift was attributed to the enhanced acceptor ability of the triazine core upon binding cations. [93] Such systems can be used for visual and distinct detection of both protons and metals ions.…”

“…SM7.1 also exhibited a similar shift upon stepwise complexation of Mg 2+ (Figure 6A), whereas SM7.2 exhibited a blue shift upon complexation with Zn 2+ (Figure 6B). The initial blue shift occurs due to the decreased ICT donor capacity of the amino‐donor‐type receptors on binding with cations and the second red shift was attributed to the enhanced acceptor ability of the triazine core upon binding cations [93] . Such systems can be used for visual and distinct detection of both protons and metals ions.…”

Molecular Tuning Nanoarchitectonics for Molecular Recognition and Molecular Manipulation

“…Designing of multiple binding sites for optimized binding motif and possible outputs such as photonic responses are commonly researched for various targets. Muraoka developed 1,3,5‐triazine‐cored star‐shaped (donor‐π) 3 ‐acceptor units with receptor residues such as 1‐aza‐15‐crown‐5‐ether and dipicolylamino (Figure B) for cation sensing through intramolecular charge transfer process . Kim and co‐workers reported fluorescence turn‐on detection of Zn 2+ ion using (E)‐1‐((((1Hbenzo[d]imidazol‐2‐yl)methyl)imino)methyl)naphthalen‐2‐ol as a sensing receptor (Figure C)…”