In this paper, we describe here the first room temperature π‐conjugated liquid based on N‐heteroacene framework showing a fluorescent property. This π‐conjugated liquid N‐heteroacene molecule is composed of branched‐long alkoxy chains and thiophene moieties. Also, N‐heteroacene‐based liquid itself can function as a stimuli‐responsive photofunctional material unlike room temperature π‐conjugated liquids reported previously. When a coated film prepared from this liquid was exposed to HCl vapor, an adsorption of HCl molecules occurred accompanied to the change in color of film from yellow to deep yellow. Moreover, emission colors of a coated film markedly changed from blue to yellow. This result indicates that this π‐conjugated liquid N‐heteroacene can function as stimuli‐responsive functional material.

We have designed and synthesized two room-temperature-fluorescent π-conjugated liquids based on the N-heteroacene framework (1 and 2). These two π-conjugated liquids, which contained one and two thiophene rings, respectively, exhibited different electronic properties and rheology behaviors. Single-crystal X-ray analysis of dithiophene-appended compound 4 revealed that two thiophene rings hindered the interactions of the imino N atoms with acids through the formation of interactions between the S atoms of the thiophene rings and the imino N atoms of the pyrazine group. On the other hand, monothiophene-appended molecules 1 and 3 each contained an unhindered imino N atom on the opposite site to the thiophene ring. Upon dissolving various acids with different pK values in compounds 1 and 2, these slight structural differences gave rise to marked differences in their acid-response behaviors, thereby resulting in the emission of variously colored fluorescence in the liquid state. Furthermore, when acids with lower pK values was dissolved in compounds 1 and 2, phase transition occurred from an isotropic liquid state to a self-organized liquid-crystalline phase.

Herein, we report a stimulus-responsive supercooled πconjugated liquid and the possibility of its application in rewritable media. Supercooled liquid 1 showed a dramatic change in its photoluminescent color upon the transformation from liquid 1l (yellow emission) to solid 1s (green emission). These phenomena were revealed by fluorescence spectra as well as lifetime decay profiles.

Two room‐temperature fluorescent π‐conjugated liquids based on a N‐heteroacene framework were designed and prepared with one or two thiophene rings. These liquid materials can be utilized as inks to be coated on substrates and displayed different electronic properties and rheology behavior; for example, fluorescent colors were light blue and blue, respectively. Moreover, dissolving various acids substances in these liquids gave rise to different fluorescent colors. Furthermore, when acids with lower pKa values were dissloved in these liquids, a phase transition occurred to a self‐organized liquid‐crystalline phase. More information can be found in the Full Paper by Kyosuke Isoda et al. on page 2619 in Issue 18, 2018 (DOI: 10.1002/asia.201800631).