Intermolecular H-bonding Interactions Research Articles

Efficient deep-blue fluorescent OLEDs based on a D‒π‒A emitter profiting from intramolecular hydrogen bonds and a hybridized excited state.

High performance deep-blue emitters with a Commission International de l'Eclairage (CIE) coordinate of CIEy ≤ 0.08 are highly desired in ultrahigh-definition displays. Herein, we designed and synthesized an efficient D‒π‒A deep-blue emitter, 2-(6-([1,1':3',1''-terphenyl]-5'-yl)pyridin-3-yl)-1-phenyl-1H-phenanthro[9,10-d] imidazole (mPTPH), using the synergistic effect of intramolecular hydrogen bond (H-bond) and hybridized excited state. Single-crystal structure analysis confirmed that there exist intra- and intermolecular H-bond interactions which could inhibit the structure vibration and increase photoluminescence efficiency. The photophysical and theoretical results show that mPTPH exhibited hybridized local and charge-transfer (HLCT) feature with strong deep-blue emission. Ultimately, the non-doped device based on mPTPH exhibited high maximum luminance of 20610 cd m-2. The doped device achieved high maximum external quantum efficiency of 5.4% and small efficiency roll-off with deep-blue emission peak of 413 nm and CIE coordinate of (0.16, 0.08).

Mechanically customizable lignin bio-elastomers based on tailorable multiscale microstructures

The development of bio-based polyurethanes (PU) elastomers with well-designed multiscale microstructures to customize their mechanical performances was desired, but remained an ongoing challenge. Herein, a novel strategy of integrating tailorable hard-soft nanophases with multiple hydrogen bond (H-bond) interactions was proposed to construct mechanically customizable PU bio-elastomers. In this strategy, highly reactive lignin with high hydroxyl contents was employed as bio-polyol monomer reacting with hexamethylene diisocyanate (HDI) to construct carbamate bonds with a function of tailoring H-bond degree via altering the feeding ratio of lignin. The rigid lignin cooperating with HDI as hard segments self-assembled to generate phase separated nanostructures. Consequently, the integration of well-defined hard-soft nanophases and multiple H-bond interactions in the synthesized lignin-based PU (LPU) achieved excellent and customizable mechanical performances ranging from highly elastic rubber to highly stiff plastic with ultrahigh strength of 72.8 MPa and unprecedented modulus of 3.5 GPa. Impressively, rubber-like LPU elastomers could recover 90 % of initial stress even after 500 stretching cycles, indicating fascinating resilience and fatigue resistance. More especially, rigid LPU plastics with fully hard domains and dense H-bond networks could be transformed into flexible and bendable paper-like elastomers once eliminating intermolecular H-bond interactions under 60 °C hot water. Thus, this work provides a feasible and promising approach to construct supramolecular PU elastomers with excellent and customizable mechanical performances to extend their on-demand applications.

Comparative Study of Two Spectral Methods for Estimating the Excited State Dipole Moment of Non-Fluorescent Molecules.

The electronic absorption spectral characteristics of cycloimmonium ylids with a zwitterionic structure have been analyzed in forty-three solvents with different hydrogen bonding abilities. The two ylids lack fluorescence emission but are very dynamic in electronic absorption spectra. Using the maximum of the ICT band, the goal was to establish an accurate relationship between the shift of the ICT visible band and the solvent parameters and to estimate two of the descriptors of the first (the) excited state: the dipole moment and the polarizability. Two procedures were involved: the variational method and the relationships of the Abe model. The results indicate that the excited state dipole moment of the two methylids decreases in the absorption process in comparison with the ground state. The introduction of a correction term in the Abe model that neglects the intermolecular H-bonding interactions leads to a more accurate determination of the two descriptors. The strong solvatochromic response of both ylids has been further applied in distinguishing the solvents as a function of their specific parameters. Principal component analysis was applied to five selected properties, including the maximum of the charge transfer band. The results were further applied to discriminate several binary solvent mixtures.

Comprehensive insights of a Salamo-like Oligo(N,O-donor) ligand and its self-assembled di-nuclear Mn(III) and tetra-nuclear Cd(II) complexes

The self-assembled di-nuclear Mn(III) & tetra-nuclear Cd(II) salamo-like oligo(N,O-donor) complexes, [Mn2(L)2(CH3OH)2]·4CH3OH (1) and [Cd4(L)2(η-OAc)2(CH3OH)2] (2) have been constructed successfully applying the measure of solvent evaporation and characterized structurally by X-ray diffraction analyses of single crystal, IR & UV visible analyses. The single crystals of the salamo-like oligo(N,O-donor) compound H3L have been obtained by wet-chemical technique, its established structure is H3L∙CH3OH. The structure of complex 1 is centrally symmetrical, and both Mn(III) atoms are hexa-coordination and have slightly distorted octahedral geometries. There are two sets of intermolecular H-bonding interactions which are connected with adjacent units of the Mn(III) complexes and form a two-dimensional network structure. For the complex 2, all of the Cd(II) atoms are also hexa-coordination and possess slightly twisted octahedral configurations. And five groups of intermolecular H-bonding interactions form a honeycomb shaped three-dimensional supramolecular structure. Additionally, the intermolecular interactions of H3L, complexes 1 and 2 have been quantified by Hirshfeld surface analysis for further study. Fluorescence emission spectra of H3L, complexes 1 and 2 were also investigated.

Tannic acid self-aggregation and adsorption onto a polyethersulfone membrane: An all-atom molecular dynamics study

Atomic scale modeling is crucial for characterizing the interactions responsible for fouling, which is a major limitation in the use of membrane filtration technologies for the recovery of polyphenols. In this work, a methodology to model a porous ultrafiltration polyethersulfone (PES) membrane is presented. Subsequently, various systems containing tannic acid (TA) molecules at different concentrations (9 or 30 g/L) were studied, with two additional systems incorporating a PES membrane, through 100 ns all-atom molecular dynamics simulations. The results show that up to 90% of the TAs are self-aggregated, associated with the formation of intermolecular H-bond and π-stacking interactions. Furthermore, adsorption of 48–67% of the TAs onto PES was observed. TA-PES H-bond and π-stacking interactions are also formed. The number of adsorbed TAs molecules over time and the evolution of the mean size of TA aggregates exhibits similar temporal trends, suggesting a parallel progression in both phenomena. Moreover, the same atoms were involved in both aggregation and adsorption, leading to the conclusion that the two phenomena compete. These results shed light on the fouling mechanism, which appears to occur through the formation of a cake layer combined with adsorptive fouling, and could support the design of new antifouling agents adapted for polyphenol filtration.

Metal-free functionalization of tyrosine residues in short peptides and study of the morphological alterations.

An efficient functionalization of tyrosine residues in phenolic regions is achieved under metal-free conditions. The strategy involves the conversion of a tyrosine residue to 4-amino phenylalanine or 4-amino-3-methoxy phenylalanine in short peptides through a controlled oxidative dearomatization. This transformation is achieved in one pot with good yields and excellent regioselectivity. Consequently, the self-assembly of the peptide compounds has been studied at the nanoscopic level before and after functionalization. The results suggest that the peptide derivatives comprising amide groups promote intermolecular H-bonding interactions and the difference in -OH and -NH2 functional groups is found to be responsible for the morphological changes. Morphological transitions from 1D nanowires to 2D nanosheets were observed during functional group modification.

Description of an original molecular ordering process into a disordered crystalline form: the atypical low-temperature transformation of the disordered form III of linezolid.

Form III of linezolid was prepared by heating the commercial form above 150 °C and subsequently analyzed upon cooling down to -160 °C, by low- and high-frequency Raman spectroscopy, differential scanning calorimetry and powder X-ray diffraction (PXRD). It was observed that form III was preserved down to 0 °C. At lower temperatures a soft mode was clearly detected by low-frequency Raman spectroscopy associated with the detection of additional Raman bands distinctive of additional intermolecular H-bond interactions. Raman spectroscopy investigations performed in a wide frequency range revealed a continuous transformation characterized by both displacive and order-disorder signatures. By contrast, PXRD highlighted the absence of symmetry breaking, Bragg peaks being still indexed in the same unit cell from room temperature down to -160 °C. Additionally, a significant broadening of Bragg peaks was observed with decreasing temperature interpreted as being a consequence of a distribution of frozen molecular conformations.

Supramolecular polymerization of [6]helicene-based cyano-luminogens: on the overall efficiency of self-assembled circularly polarized emitters.

The synthesis of the [6]helicene-based luminophores 1 and 2 is reported. These chiral systems, endowed with cyano-stilbene fragments, form supramolecular polymers by the operation of intermolecular H-bonding interactions between the amides present in the peripheral side chains. The dissimilar disubstitution of 1 and 2 plays a crucial role in their self-assembling features. Thus, 1 does not show an efficient π-stacking of the central aromatic moiety. Instead, its self-assembling process results in a zig-zag arrangement of the monomeric units to form the aggregated species. On the other hand, 2 presents an efficient overlap of the aromatic backbones that affords a co-facial arrangement of the monomeric units. The solvent-dependent studies indicate that both [6]helicenes self-assemble following a cooperative supramolecular polymerization mechanism with a higher degree of cooperativity and stability for compound 2. The enantioenriched samples of both 1 and 2 display a rich dichroic pattern that changes when the supramolecular polymerization takes place. Furthermore, the presence of the cyano-stilbene moieties gives rise to an aggregation induced emission effect. The inherent chirality of both the monomeric and aggregated species of 1 and 2 provides the systems with CPL-emitting properties, presenting a remarkable overall CPL-efficiency, quantified by the BCPL parameter, that increases upon supramolecular polymerization.

Preparation and Interfacial Properties of Hydroxyl-Containing Polyimide Fibers.

Developing polyimide (PI) fibers with excellent interfacial adhesion and high mechanical properties for the PI fiber-reinforced polymer matrix composites (PFRPs) industry has been challenging. In this work, 4,4'-diamino-(1,1'-biphenyl)-3,3'-diol (HAB) diamine was introduced into the rigid molecular chains, and the high-performance PI fibers, presenting an interfacial shear strength (IFSS) value of 46.33 MPa, tensile strength of 2.62 GPa, and modulus of 100.15 GPa, were successfully manufactured when the content of HAB in mixed diamines was 30 mol %. Fourier transform infrared (FTIR) spectroscopy identified the presence of intermolecular H-bonding interactions, and 2D small-angle X-ray scattering indicated that the introduction of HAB moiety contributed to reducing the radii of microvoids in the fibers, which were considered to be the key factors leading to a significant enhancement in the mechanical properties of the fibers. X-ray photoelectron spectroscopy (XPS) and the static contact angle intuitively illustrated that the synthetic fiber surface contained active hydroxyl groups. The IFSS value of PI fiber/epoxy resin composites (PI/EPs) was 56.47 MPa when the content of HAB reached 70 mol %. Failure morphologies confirmed that the interfacial adhesion of PI/EPs was enhanced owing to the surface activity of PI fibers. Consequently, this study provides an effective strategy to the long-standing problems of high mechanical performances and poor surface activity for traditional PI fibers used in the PFRPs industry.

Weak intra and intermolecular interactions via aliphatic hydrogen bonding in piperidinium based ionic Liquids: Experimental, topological and molecular dynamics studies

Hydrogen bonding interaction plays an important role in the stability of the building blocks of various materials. In present work, both intra- and inter- molecular aliphatic H-bond interactions stabilize piperidinium based ionic liquids (ILs: MPDNP, PPDNP, BPDNP and HPDNP) and play crucial role on physical properties of these ILs. Further, the significance of multiple intermolecular aliphatic H-bonding interactions in the formation of molecular clusters, ion-pair, dimeric ion-pairs, and also corrugated sheet array of ILs has been investigated here. UV–vis study of these ILs has also been performed to understand the electronic properties of these ILs in solution. The DSC, TGA, SCXRD, vibrational spectroscopic techniques have been employed to understand the effect of intra and intermolecular aliphatic hydrogen bonding interaction on physical property and molecular cluster formation of ILs in their ambient phases. The DSC and TGA studies demonstrate that the intermolecular interaction between cation and anion remains nearly unvaried on increasing of alkyl chain length but the physical properties of ILs changes. SCXRD and vibrational spectroscopic techniques describe the presence of aliphatic H-bonding interaction between ion pairs, dimeric ion-pairs and corrugated sheet having contacts in the range 2.46–2.63 Å. NBO analysis is performed to calculate the second order stabilization energy for better understanding of the intramolecular interactions at a molecular level. The second order stabilization energy for the transfer lone pair charge of oxygen to antibonding orbital of CH is measured in the range of 3.46–3.73 Kcal/mol for ILs. Topological and ab initio molecular dynamics (AIMD) simulations studies are performed to get closer insight of underlying interactions and the stability of ILs. AIMD study depicts that the total energy of IL attains a maximum of −1045.84 a.u. close to 100 fs, whereas relatively low energy is measured between 250 and 350 fs.

Induction and rationalization of supramolecular chirality in a Zn(II)porphyrin dimer using chiral substrates: Role of substrates in the architectural selectivity

A flexible Zn(II)porphyrin dimer has been utilized as an efficient host for the selective binding of several diols and diamines as substrates. Stepwise formation of a 1:1 host-guest polymer and 1:2 host-guest monomer via intermolecular self-assembling and disassembling processes, has been demonstrated with a series of diamine/diols. Transfer of chirality from the molecular to the supramolecular level has been rationalized with structural elucidation. The formation of the 1:1 host-guest polymer displays a bisignate CD couplet. X-ray structure demonstrates the presence of both clockwise and anticlockwise conformers, however, the conformer formed as per pre-organization in the substrate chirality contributes more towards the overall CD couplet in solution. The addition of the substrate in excess leads to the inversion of the CD couplet due to the formation of the monomeric complex. Architectural selectivity has been illustrated for the 1:1 host-guest complexation by simply tuning the length of the substrates. Crystallographic characterizations revealed linear 1D polymeric structures for the 1:1 host-guest complexes with longer diamines while shorter substrates stabilize cyclic dimer via intermolecular H-bonding between the urea bridge (cis-NH-CO-) of the two porphyrin dimers. Interestingly, the molecular structure of 1:1 host-guest complexes with diols displays a linear polymer despite the shorter length of the substrates. Along with weaker coordination of the alcoholic oxygen towards the Zn(II) ion, the presence of bulky substituents at the coordinating sites of the diols renders the formation of intermolecular H-bonding interactions. Thus, the nature of metal ion and their binding affinity towards the substrate, host-guest size complementarity, and the bulk of the substituents contribute cumulatively towards the architectural selectivity. The cyclic dimers display larger upfield shifts of the substrate protons in the 1H NMR spectra as compared to the linear polymers. Moreover, the computational calculations further substantiate the experimental observations.

Synthesis, crystal structure, molecular dynamics, docking and in-vitro studies of cyclododecanonethiosemicarbazone, a promising anti tuberculosis agent

Cyclododecanonethiosemicarbazone (CDT), crystallises in triclinic crystal system in spacegroup P-1 having unit cell parameters as a = 5.6152(2)Å, b = 8.3747(4) Å, c = 16.1901(7) Å, α = 91.186(2)°, β = 90.880(2)° and γ = 108.014(2)°, V = 723.68(5) Å3 and Z = 2.The macrocyclic ring structure shows close resemblance to the most stable conformation for a 12 membered aliphatic cyclic ketone, where three C-C bonds are present on each side of the heavy atom framework's square structure. Existence as thione form of the compound is confirmed by IR, NMR and Crystallographic data. There is extensive electron delocalisation along its thiosemicarbazone moiety. A number of short term interactions, including three intermolecular H-bonding interactions involving each S, forms infinite interlinked chains of molecules along a axis. Results of anti tuberculosis activity studies reveal that minimum inhibitory concentration (MIC) of CDT is 800 µg/mL for the test organism Mycobacterium smegmatis. Hirshfeld surface analysis, docking and molecular dynamics studies suggest stable protein –ligand binding with the related 1TEX protein.

Theoretical insight into the acidity and cooperativity effect of the LLM-105∙(HNO3)2 system.

In order to reveal the nature of the acidity in explosive product, the acidities and cooperativity effects from the intermolecular H-bonding interactions in the LLM-105∙∙∙(HNO3)2 ternary systems were investigated at the B3LYP/6-311 + + G** and M062X/6-311 + + G** levels, with the integral equation formalism polarized continuum model (IEFPCM) based on the self-consistent-reaction-field. The results show that for the ternary systems, the intermolecular H-bonding interactions are stronger than those in the binary complexes, resulting in the lower [H+] concentrations and larger pKa1 values upon the ternary-complex formations. However, there is no obvious correlation between the acidities and cooperativity effects or APT charges of the H atoms involving the H-bonds. Surface electrostatic potential (ESP) and reduced density gradient are used to reveal the nature of the H-bond and acidity. Interestingly, the acidity is closely related to the ESPs of the H atom (VS,H) involving the intermolecular H-bond, but not to the statistical quantities. This is mainly because both acidity and VS,H are the local properties of system, whereas the cooperativity and statistical quantity of ESP are the global property.

Quantitative Measurement of Cooperativity in H-Bonded Networks.

Cooperative H-bonding interactions are a feature of supramolecular networks involving alcohols. A family of phenol oligomers, in which the hydroxyl groups form intramolecular H-bonds, was used to investigate this phenomenon. Chains of intramolecular H-bonds were characterized using nuclear magnetic resonance (NMR) spectroscopy in solution and X-ray crystallography in the solid state. The phenol oligomers were used to make quantitative measurements of the effects of the intramolecular interactions on the strengths of intermolecular H-bonding interactions between the H-bond donor on the end of the chain and a series of H-bond acceptors. Intramolecular H-bonding interactions in the chain increase the strength of a single intermolecular H-bond between the terminal phenol and quinuclidine by up to 14 kJ mol-1 in the n-octane solution. Although the magnitude of the effect increases with the length of the H-bonded chain, the first intramolecular H-bond has a much larger effect than subsequent interactions. H-bond cooperativity is dominated by pairwise interactions between nearest neighbors, and longer range effects are negligible. The results were used to develop a simple model for cooperativity in H-bond networks using an empirical parameter κ to quantify the sensitivity of the H-bond properties of a functional group to polarization. The value of κ measured in these systems was 0.33, which means that formation of the first H-bond increases the polarity of the next H-bond donor in the chain by 33%. The cumulative cooperative effect in longer H-bonded chains reaches an asymptotic value, which corresponds to a maximum increase in the polarity of the terminal H-bond donor of 50%.

Synthesis, spectroscopic, topological, hirshfeld surface analysis, and anti-covid-19 molecular docking investigation of isopropyl 1-benzoyl-4-(benzoyloxy)-2,6-diphenyl-1,2,5,6-tetrahydropyridine-3-carboxylate

Isopropyl 1-benzoyl-4-(benzoyloxy)-2,6-diphenyl-1,2,5,6-tetrahydropyridine-3-carboxylate (IDPC) was synthesized and characterized via spectroscopic (FT-IR and NMR) techniques. Hirshfeld surface and topological analyses were conducted to study structural and molecular properties. The energy gap (Eg), frontier orbital energies (EHOMO, ELUMO) and reactivity parameters (like chemical hardness and global hardness) were calculated using density functional theory with B3LYP/6–311++G (d,p) level of theory. Molecular docking of IDPC at the active sites of SARS-COVID receptors was investigated. IDPC molecule crystallized in the centrosymmetric triclinic (P1¯) space group. The topological and Hirshfeld surface analysis revealed that covalent, non-covalent and intermolecular H-bonding interactions, and electron delocalization exist in the molecular framework. Higher binding score (-6.966 kcal/mol) of IDPC at the active site of SARS-COVID main protease compared to other proteases suggests that IDPC has the potential of blocking polyprotein maturation. H-bonding and π-cationic and interactions of the phenyl ring and carbonyl oxygen of the ligand indicate the effective inhibiting potential of the compound against the virus.

Organic Electroluminescent Materials Possessing Intra- and Intermolecular Hydrogen Bond Interactions: A Mini-Review.

Organic light-emitting diodes (OLEDs) have become the predominant technology in display applications because of their superior light weight, flexibility, power conservation, and environmental friendliness, among other reasons. The device’s performance is determined by the intrinsic properties of organic emitters. The aggregation structure of emitters, in particular, is crucial for color purity and efficiency. Intra- and intermolecular interactions, such as hydrogen bonds (H-bonds), can reduce structural vibrations and torsions, which affect the stability of emitting layer films and optoelectronic properties of emitting materials. Hence, by regulating the H-bond interaction, the desired properties could be obtained. This mini-review focuses on the influence of intra- and intermolecular H-bond interactions on the optoelectronic properties of high-performance emitters.

Tautomeric, spectroscopic, electronic and NLO analyses of purpald (4-amino-3-hydrazino-5-mercapto-1,2,4-triazole)

Thione and thiol tautomeric structural forms of 4-Amino-3-hydrazino-5-mercapto-1,2,4-triazole (purpald) were theoretically analyzed based on energetic and molecular structural geometry by using the DFT/B3LYP method with the 6–311++G(3df,3pd) basis set. The existence of the inter-molecular H-bond or close contact interactions within solid state crystal packing diagram was determined by Hirshfeld surface analysis. The experimental and theoretical investigations on the NMR chemical shifts were used for determination of more dominant tautomeric form between thione and thiol structures. The characteristic vibrations of functional groups within the compound were analyzed with IR and Raman wavenumbers. The experimental and computational UV spectral study was made to examine nature of the intra-molecular electronic transitions within DMSO solution phase. Some global quantum mechanical descriptors were determined with FMOs (HOMO and LUMO) investigation. The presence of hyperconjugation interactions within NBO analysis helped to explain thione-thiol tautomeric equilibrium and inter-molecular N4-H15···N8′ and N7′-H12′···S9 interactions within thione dimeric form. The reactive sites of all tautomeric forms were examined with MEP surface analysis. The static NLO properties were theoretically investigated to test whether all tautomeric forms have a non-linear optical material profile. A theoretical investigation on the molar volume, dielectric constant and refractive index of the compound was carried out at mentioned computational level of theory. Comparison and detailed presentation of the structural and spectral experimental and calculated related properties of the compound were done in this study.

ICT based photoacid probe for microsolvation and H-bonding assisted proton transfer process from solute to solvents

The present work recognises 2-(3,4-Dihydroxybenzylidene)malononitrile (Hy34DC) as a photoacid and intramolecular charge transfer (ICT) probe for proton transfer process from solute to solvent at the ground and excited state. Microsolvation and intermolecular H-bonding interactions play a significant role in enhancing the proton transfer process. Solvent-dependent enhancement of proton transfer process is observed comparing the relative intensity of ICT band from UV–Vis results at ground state. Solvent-specific dual fluorescence properties of Hy34DC are also detected in solution. Polar protic solvents boost the proton transfer process from solute to solvent via intermolecular H-bonding interaction. DFT calculations are also performed to investigate the solvent-dependent solute–solvent interactions.

Nitrogen doped activated carbon derived from chitosan/hexamethylenetetramine: structural and CO2 adsorption properties

Chitosan and chitosan/hexamethylenetetramine (HMT) macrospheres were prepared respectively by dropping the solution of chitosan and chitosan/HMT (in wt/wt ratios of 1:1 and 1:3) in aq. NaOH solution. Here, HMT served as an additional nitrogen precursor for in situ N-doping with chitosan derived activated carbon (AC). The as-formed macrospheres were impregnated using ZnCl2, freeze-dried and carbonized at 500 °C under inert atmosphere to yield ACs of size ranging from 2.5 to 2.8 mm. All the samples were characterized using SEM, EDS, CHNS Analyzer, TGA, FT-IR, Raman, XRD and BET surface area analyzer. All the samples showed mesoporous characteristics. The surface area of the AC without HMT, with 1:1 HMT and 1:3 HMT were 391.502, 259.017 and 111.717 m2/g respectively. Similarly, the pore volumes of AC without HMT, with 1:1 HMT and 1:3 HMT were 0.138, 0.095 and 0.075 cc/g respectively. The chitosan/HMT derived AC possessed higher N-content and better thermal stability, however exhibited lower surface properties with increasing HMT content. The CO2 adsorption capacity of chitosan derived AC was 97.98 mg/g while that of AC with 1:1 HMT and 1:3 HMT were 72.95 mg/g, 55.11 mg/g respectively at 25 °C and 1 bar. Deterioration in adsorption capacity of chitosan/HMT derived AC may be attributed to the physical cross-linking of chitosan polymer chains induced by increase in pH with addition of HMT and also the intermolecular H-bonding interaction between HMT and chitosan, which in turn reduces the surface area of as-formed N-doped ACs progressively.

Expanding the Scope of Metastable Species in Hydrogen Bonding-Directed Supramolecular Polymerization.

We reveal unique hydrogen (H‐) bonding patterns and exploit them to control the kinetics, pathways and length of supramolecular polymers (SPs). New bisamide‐containing monomers were designed to elucidate the role of competing intra‐ vs. intermolecular H‐bonding interactions on the kinetics of supramolecular polymerization (SP). Remarkably, two polymerization‐inactive metastable states were discovered. Contrary to previous examples, the commonly assumed intramolecularly H‐bonded monomer does not evolve into intermolecularly H‐bonded SPs via ring opening, but rather forms a metastable dimer. In this dimer, all H‐bonding sites are saturated, either intra‐ or intermolecularly, hampering elongation. The dimers exhibit an advantageous preorganization, which upon opening of the intramolecular portion of the H‐bonding motif facilitates SP in a consecutive process. The retardation of spontaneous self‐assembly as a result of two metastable states enables length control in SP by seed‐mediated growth.