Thermochromism of Polydiacetylenes Containing Robust 2D Hydrogen Bond Network of Naphthylmethylammonium Carboxylates

Abstract

We investigated the molecular packing structure and the solid-state polymerization behavior of diacetylene compounds containing a naphthylmethylammonium carboxylate group in the side chain, which forms robust and two-dimensional hydrogen bond networks. The resulting polydiacetylenes (PDAs) showed thermochromic behaviors dependent on the structure of the substituents in the side chain. The maximum wavelength of the absorption bands in the UV-vis spectra of the poly(m,0-DA-Naph)s, which were obtained by the polymerization of the 1-naphthylmethylammonium 2,4-alkadiynoates (m ) 4-13, 16), shifted to a longer wavelength region with an increase in the alkyl chain length of the side chain. The poly(m,0-DA-Naph)s showed a reversible color change upon heating in a temperature range wider than that for poly(1-naphthylmethylammonium 10,12pentacosadiynoate) [poly(12,8-DA-Naph)] due to the different position of the two-dimensional hydrogen bond network supporting the chain structures in the solid state. We further investigated the structure and chromatic properties of PDAs containing the phenylene substituent groups that are directly connected to the conjugating main chain. Eventually, we found the occurrence of the solid-state polymerization of the 4-carboxyphenylsubstituted diacetylenes as not only naphthylmethylammonium salts (m,Ph-DA-Naphs, where m ) 8, 10, 12, and 16), but also precursor carboxylic acid derivatives (m,Ph-DA-CO 2 Hs). The poly(16,Ph-DA-Naph)s showed a reversible color change upon heating, but the mechanism was different from that of the other PDAs. The thermochromism of poly(16,Ph-DA-Naph) included the conformational changes in the aromatic substituent and the conjugating backbone structure.

Synthesis, Structure, Chromatic Properties, and Induced Circular Dichromism of Polydiacetylenes with an Extended Conjugated System in the Side Chain

“…[11] The 2,4-alkadiynoic acids (m,0-DA-CO 2 Hs) were synthesized by the method described in our previous paper. [11] The 1-naphthylmethylammonium salts, m,Ph-DA-Naphs and m,0-DA-Naphs, were prepared by the quantitative reaction of m,Ph-DA-CO 2 Hs and m,0-DA-CO 2 Hs with 1-naphthylmethylamine, respectively.…”

“…[11] The 2,4-alkadiynoic acids (m,0-DA-CO 2 Hs) were synthesized by the method described in our previous paper. [11] The 1-naphthylmethylammonium salts, m,Ph-DA-Naphs and m,0-DA-Naphs, were prepared by the quantitative reaction of m,Ph-DA-CO 2 Hs and m,0-DA-CO 2 Hs with 1-naphthylmethylamine, respectively. The commercially available chiral amines, (R)-(À)-(1-cyclohexyl)ethylamine [(R)-CHA, Aldrich, 95%ee] and (S)-(þ)-(1-cyclohexyl)ethylamine [(S)-CHA, Aldrich, 95%ee], were used without further purification.…”

“…These wavelength values are greater than those for the PDAs without conjugating groups in the side chain, and similar to those for the other PDAs with an expanded p-conjugated system. [12] Previously, a more intense effect of the alkyllength dependence on the wavelength of the absorption bands was observed for the poly(m,0-DA-Naph)s. [11] This is due to the more significant effects of the alkyl stacking in the crystals including the 2D hydrogen bond networks. Namely, the more conjugated conformation of the PDA main chain is preferred in the crystals with the strong interaction between the side alkyl chains, because the repeating distance due to the alkyl chain stacking matches the repeating period of the main chain of the PDAs.…”

“…This peak completely disappeared during the photoirradiation for several hours, suggesting the higher polymerization reactivity of 16,Ph-DA-Naph due to the robust crystal structures appropriate for the solid-state polymerization supported by the 2D hydrogen bond network structure. [11,13] …”

“…[11] In the literature, only a few studies on the synthesis of PDA which includes a conjugating side group connected to the main chain have been reported. [12] In the present study, the chromatic properties of poly(m,Ph-DA-CO 2 H)s and poly(m,Ph-DA-Naph)s were examined and compared with those for poly(m,0-DA-CO 2 H)s and poly(m,0-DA-Naph)s containing no phenylene substituent (Scheme 2).…”