Reversibly/irreversibly stimuli-responsive inks based on N-heteroacene liquids

Abstract

These liquid materials can be applied into reversibly/irreversibly stimuli-responsive inks for security.

Stimuli-responsive Behaviors for Room-temperature Fluorescent Liquid Materials based on N-Heteroacenes and their Mixtures in Response to HCl Vapor and their Facile Synthesis

“…Also, the previous report has evaluated the protonated position by the single crystallographic X-ray analysis as well as 1 H NMR measurement of similar p-conjugated framework to Py and Phen. [25][26] These result suggests that the protonation of Bz and Phen occurs at imino-N atom of quinoxaline framework, whereas Py captures with proton at imino-N atom of pyridine ring. 26 Further, corresponding conjugated acids Figure 4a-c. 26,[49][50] The Commission Internationale de l'Eclairage (CIE) 1931 chromaticity diagram [53][54] in Figure 4d shows that each point for Bz, Py, and Phen before exposure to HCl vapor changes into each one after exposure, corresponding to the color change seen in the right photographs in Figure 3c.…”

“…In this study, we resolved this disadvantage by the redesigning of novel molecular structures for a series of SFLs, benzene-substituted (Bz), pyridine-substituted (Py), and phenanthrene-based quinoxaline (Phen), shown in Scheme 1. As a result, we successfully reduce the reaction step from 6 to 3 steps, compared to previous scheme, [25][26][27][28][29] increasing product yields up to 40%.…”

“…The exposure of proPy-Phen to air dominantly allows the deprotonation of proPhen with lower pKa. 26,[49][50] In contrast, proPy as conjugated acid has so higher pKa that HCl molecule could be retained in proPy films. Accordingly, the exposure of proPy-Phen to air should retain proPy and recover into Phen in the film.…”

“…As a result, the combination with each other as well as the exposure time to HCl vapor / air can provide emission color variations, which are expected to be applied into stimuli-responsive inks as security. 26…”

“…fluorescent liquid materials (SFLs) based on N-heteroacene frameworks. [25][26][27][28][29] However, SFLs reported involve disadvantage on the product yield that previously molecular designs need at least 6 steps started from commercially available compound, to afford SFLs in very low yield (<10% in total steps). In this study, we resolved this disadvantage by the redesigning of novel molecular structures for a series of SFLs, benzene-substituted (Bz), pyridine-substituted (Py), and phenanthrene-based quinoxaline (Phen), shown in Scheme 1.…”