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Adapting (4,4) Networks through Substituent Effects and Conformationally Flexible 3,2’:6’,3”-Terpyridines

ABSTRACT: Coordination networks formed between Co(NCS)2 and 4’-substituted-[1,1’-biphenyl]-4-yl-3,2’:6’,3”-terpyridines in which the 4’-group is Me (1), H (2), F (3), Cl (4) or Br (5) are reported. [Co(1)2(NCS)2]n·4.5nCHCl3, [Co(2)2(NCS)2]n·4.3nCHCl3, [Co(3)2(NCS)2]n·4nCHCl3, [Co(4)2(NCS)2]n, and [Co(5)2(NCS)2]n·nCHCl3 are 2D-networks directed by 4-connecting cobalt nodes. Changes in the conformation of the 3,2’:6’,3”-tpy unit coupled with the different peripheral substituents lead to three structure types. In [Co(1)2(NCS)2]n·4.5nCHCl3, [Co(2)2(NCS)2]n·4.3nCHCl3, [Co(3)2(NCS)2]n·4nCHCl3, cone-like arrangements of [1,1’-biphenyl]-4-yl units pack through pyridine…arene π-stacking, whereas Cl…π interactions are dominant in the packing in [Co(4)2(NCS)2]n. The introduction of the Br substituent in ligand 5 switches off both face-to-face π-stacking and halogen…π-interactions, and the packing interactions are more subtly controlled. Assemblies with organic linkers 1–3 are structurally similar and the lattice accommodates CHCl3 molecules in distinct cavities; thermogravimetric analysis confirmed that half the solvent in [Co(3)2(NCS)2]n·4nCHCl3 can be reversibly removed.

SUBMITTER: Rocco D

PROVIDER: S-EPMC8587907 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Structurally engineered molecules which can behave as stimuli-controlled mechanical nanomachines such as molecular shuttles, rotors, ratchets, and springs are important in several research areas, including molecular robotics, actuation, sensing, cargo transportation, etc. Helicenes, by virtue of their unique screw-type structures, were proposed as functional models for molecular springs; however, experimental realization has remained an elusive and unmet task until now, because of the lack of appropriate helicene molecules consisting of backbone-decorated dynamic architectures. Aiming to explore this unearthed direction, we present herein a novel class of modular flexible heterohelicenes with a stimuli (acid/base and light)-responsive core and peripheral modules. By applying pH (at core-embedded free imidazole sites) and light (at backbone-tethered dithienylethene units) stimuli, we demonstrate that these flexible heterohelicenes exhibit spring-like movement, with the reversible contraction/extension of the helical pitch. The uniquely functionalized structure of these molecules played a critical role in bestowing such capability, as revealed by crystallographic, spectroscopic and computational data. Careful assessment disclosed that the protonation/deprotonation-induced reversible generation and delocalization of positive charge throughout the π-conjugated helical rim switch the operative interactions between the π clouds of the terminal overlapping arene rings of the helicenes between repulsive and attractive, leading to extension/contraction of the helical pitch. On the other hand, in the case of the light stimulus, it was analyzed that the light-induced ring-closure of the photoactive dithienylethene units created a geometric distortion causing the helicenic wings to bend outward from the helicene rim, which resulted in extension of the helical pitch. The photo-assisted (or thermal) reverse ring-opening reaction converted the system to its original conformation, thus enabling the helicene molecule to display spring-like reversible extension/contraction motion. The new insights on the reversible dynamic features of this class of heterohelicenes under the influence of external stress would guide crucial design principles of helicene-based molecular springs for potential applications.

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Adapting (4,4) Networks through Substituent Effects and Conformationally Flexible 3,2’:6’,3”-Terpyridines

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