The phase transitions of 4-aminopyridine-based indolocarbazoles: twinning, local- and pseudo-symmetry

Abstract

The phase transitions and polymorphism of three 4-aminopyridine-based indolocarbazole analogues are analyzed with respect to symmetry relationships and twinning. Seven polymorphs were structurally characterized using single-crystal diffraction. 5NICz (the indolo[3,2,1-jk]carbazole derivative with the C atom in the 5-position replaced by N) crystallizes as a P21/a high-temperature (270 K) polymorph and as a Pca21 low-temperature (150 K) polymorph. Even though their space-group symmetry is not related by a group–subgroup relationship, the local symmetries of both belong to the same order–disorder (OD) groupoid family. Both are polytypes of a maximum degree of order and are twinned by point operations of the other polytype. 2NICz (C atom in the 2-position replaced by N) likewise crystallizes in a high-temperature (Pcca, 280 K) polymorph and a low-temperature (P21/c, 150 K) polymorph. Here, the space-group symmetries are related by a group–subgroup relationship. The low-temperature phase is twinned by the point operations lost on cooling. The crystal structure of bulk 2,5NICz (N-substitution at the 2- and 5-positions) was unrelated to 2NICz and 5NICz and no phase transition was observed. Isolated single crystals of a different polymorph of 2,5NICz, isotypic with 2NICz, were isolated. However, the analogous phase transition in this case takes place at distinctly higher temperatures (> 300 K).

Azaindolo[3,2,1‐jk]carbazoles: New Building Blocks for Functional Organic Materials

“…Compounds 2NICz, 5NICz,a nd 2,5NICz featured temperature-dependentp olymorphism and twinning, which is beyond the scope of this contribution and will be discussed in detail elsewhere. [60] Atomsw ere labeled as outlined in Figure 1. In the case of more than one crystallographically unique molecule (Z' = 2), prime characters are added to the atom names.…”

“…In both cases, the molecules are located on a( pseudo-)twofold rotationa xis;t his (pseudo)symmetry is the crucial feature of the phase transitions described elsewhere. [60] The mutual inclination of adjacent molecules with respectt ot his axis is determined by the crystal packing: In 2NICz,t he least-squares (LS) planes defined by the Ca nd Na toms of the individual aromatic planeso ft wo adjacent molecules are inclinedb y6 3.48.I n contrast, 2,5NICz exists as two polymorphs;the first is isostructural with 2NICz,w hereas in the second, adjacent molecules are perfectly coplanar (adjacent moleculesr elatedb yab + c lattice translation). In both 2,5NICz polymorphs, the molecule is 1:1d isordered with respect to the N5 atom, which is not involved in hydrogen bonding.…”

Thienopyrrolo[3,2,1-jk]carbazoles: Building Blocks for Functional Organic Materials

“…Inspired by these results, we set out to reverse the effect of increased electron deficiency by replacement of one benzene unit of the ICz scaffold with thiophene. Substitution of one benzene ring with thiophene should increase the electron-donating power and destabilize the HOMO level of the annulated system, yet retain planarity, which is an important feature for intermolecular interactions, the overall alignment, and thus interaction of individual molecules in the solid state. , Accordingly, three novel thienopyrrolo­[3,2,1- jk ]­carbazoles were prepared.…”

Thienopyrrolocarbazoles: New Building Blocks for Functional Organic Materials

“…Substitution of one benzene ring by thiophene should increase the electron donating power and the HOMO level of the annulated system, yet retaining planarity, which is an important feature for intermolecular interactions and the overall alignment and thus interaction of individual molecules in the solid state. 25,30 Accordingly, three novel thienopyrrolocarbazoles were prepared.…”