Probing the Role of Glycol Chain Lengths in π-Donor–Acceptor [2]Pseudorotaxanes Based on Monopyrrolo-Tetrathiafulvalene and Cyclobis(paraquat-p-phenylene)

Abstract

We have investigated and quantified the role that the glycol chain length has on the strength of the noncovalent bonding interactions taking place between cyclobis(paraquat-p-phenylene) (CBPQT) and five different monopyrrolo-tetrathiafulvalene (MPTTF) derivatives that only differ in the length of the N-substituted glycol chain. The MPTTF derivatives were used to form [2]pseudorotaxanes by mixing them with CBPQT. The binding constants (K) associated with the complexation process leading to the formation of the [2]pseudorotaxanes were obtained using the UV-vis-NIR dilution method and the [2]pseudorotaxanes were characterized structurally using H NMR spectroscopy. These experimental investigations clearly indicate that the glycol chains provide additional stability to the [2]pseudorotaxanes findings that were further supported by density functional theory (DFT) studies. The DFT calculated superstructure of the [2]pseudorotaxane 3⊂CBPQT reveal that [C-H···O] hydrogen bonding interactions between the acidic α-H protons in CBPQT and the oxygen atoms present in the glycol chain can take place on the exterior of the [2]pseudorotaxane. However, the length of the glycol chain is of paramount importance and the present studies show that the first and second oxygen atom in the [2]pseudorotaxanes 2-5⊂CBPQT are engaged in [C-H···O] hydrogen bonding interactions with CBPQT, whereas the third and fourth oxygen atoms are not.

Naphtho[1,2‐b:5,6‐b′]dithiophene Building Blocks and their Complexation with Cyclobis(paraquat‐p‐phenylene)

“…To account for solvation an implicit Poisson‐Boltzmann solvation model was used to simulate a solution of MeCN ( R 0 = 2.2 Å; ε = 37.5). This combination of functional, basis set, and solvent model has previously been used to describe the structural and energetic properties of related superstructures and mechanically interlocked molecules , , …”

“…It has been concluded[9a], [12b], that the most electron rich (i.e., the stronger π‐electron donors) form more stable host–guest complexes with the CBPQT 4+ ring. Most recently, it has been demonstrated that ethylene glycols can also assist the complexation process[12b], between TTF derivatives and CBPQT 4+ by forming tertiary (3°) superstructures . Consequently, several catenanes and rotaxanes incorporating TTF derivatives and CBPQT 4+ have been reported in the last two decades.…”

Redox‐Active Monopyrrolotetrathiafulvalene‐Based Rotaxane Incorporating the Dihydroazulene/Vinylheptafulvene Photo/Thermoswitch

“…Preliminary structures for geometry optimization have been generated by merging CBPQT 4+ from previous work and a DHA crystal structure [CCDC 792112] followed by dynamics calculations in Maestro 10 release 2016–2 Schrödinger using MMFFS as the force field, as structure search method to find 1000 superstructures. From these minimized superstructures, 10 were chosen for optimization at higher level of theory which was done stepwise with HF/STO‐3G, HF/6‐31G, HF/6‐31G* and finally in HF/6‐31+G* using a MeCN PCM solvent model using quadratically convergent SCF procedure .…”

Tetrathiafulvalene – a redox-switchable building block to control motion in mechanically interlocked molecules

“…In later reports, differently substituted TTF derivatives as for example 2 , 4 , and 5 have been investigated towards their binding to host 3 [ 24 , 59 – 63 ]. π-Electron-rich TTFs form significantly stronger donor–acceptor complexes as π-electron-poor TTFs.…”

“…π-Electron-rich TTFs form significantly stronger donor–acceptor complexes as π-electron-poor TTFs. However, also the type of substituent on the TTF moiety plays a role in terms of weak secondary binding interactions such as hydrogen bonds [ 63 ]. For example TTF 5 which is substituted by ethylene glycol chains displays a high association constant of K a = 50,000 M −1 in acetonitrile.…”