Showing papers on "Substituent published in 2020"

Highly Efficient All-Small-Molecule Organic Solar Cells with Appropriate Active Layer Morphology by Side Chain Engineering of Donor Molecules and Thermal Annealing.

Abstract: It is very important to fine-tune the nanoscale morphology of donor:acceptor blend active layers for improving the photovoltaic performance of all-small-molecule organic solar cells (SM-OSCs). In this work, two new small molecule donor materials are synthesized with different substituents on their thiophene conjugated side chains, including SM1-S with alkylthio and SM1-F with fluorine and alkyl substituents, and the previously reported donor molecule SM1 with an alkyl substituent, for investigating the effect of different conjugated side chains on the molecular aggregation and the photophysical, and photovoltaic properties of the donor molecules. As a result, an SM1-F-based SM-OSC with Y6 as the acceptor, and with thermal annealing (TA) at 120 °C for 10 min, demonstrates the highest power conversion efficiency value of 14.07%, which is one of the best values for SM-OSCs reported so far. Besides, these results also reveal that different side chains of the small molecules can distinctly influence the crystallinity characteristics and aggregation features, and TA treatment can effectively fine-tune the phase separation to form suitable donor-acceptor interpenetrating networks, which is beneficial for exciton dissociation and charge transportation, leading to highly efficient photovoltaic performance.

Inhibitive and adsorption behavior of thiadiazole derivatives on carbon steel corrosion in CO2-saturated oilfield produced water: Effect of substituent group on efficiency

Abstract: Three thiadiazole derivatives with different substituent groups, 2-(benzylthio)-5-methyl-1,3,4-thiadiazole(BMT), 2-(benzylthio)-5-(butylthio)-1,3,4-thiadiazole(BBT), and 5-(benzylthio)-1,3,4-thiadiazole-2-thiol(BTT), were synthesized and studied as the corrosion inhibitors for N80 carbon steel in CO2-saturated oilfield produced water. It is found that the synthesized thiadiazole derivatives could effectively inhibit the corrosion of N80 carbon steel by chemisorption. The corrosion inhibition performance of the organic compounds is in the order: BTT > BBT > BMT. The theoretical calculations indicate that the tautomeric transformation from thiol-BTT to thione-BTT may be responsible for the high inhibition performance of BTT.

Novel cage-like MOF for gas separation, CO2 conversion and selective adsorption of an organic dye

Abstract: By incorporating the F substituent in tetrazolate–carboxylate ligands and combining the dipyridyl co-linkers, novel Zn-MOF, [(CH3)2NH2][Zn1.5(μ3-O)0.5(F-tzba)1.25(bpy)0.25(μ2-F)0.5]·2DMF·2H2O (1) (F-H2tzba = 2-F-4-(1H-tetrazol-5-yl) benzoic acid, bpy = 4,4′-bipyridine), was constructed. 1 was based on an unprecedented 12-connected hexanuclear cluster and formed an fcu topological framework, which contained intriguing 3D polar pores formed by intersected octahedral and tetrahedral cages with the modification using F. The framework not only showed high adsorption capacity for CO2, C2H2, and C2H6 but also exhibited excellent selective capture for CO2, C2H2, and C2H6 over CH4 and C2H2 over CO2 at 298 K. The framework as a Lewis acid heterogeneous catalyst also displayed highly efficient catalytic activity in the cycloaddition reaction of CO2 with different epoxides to produce cyclic carbonate chemicals. Grand canonical Monte Carlo simulations were studied to identify the different CO2, C2H2 and C2H6 binding sites as well as the catalytic interactions between the framework and the propylene oxide substrate. Simultaneously, the MOF could selectively adsorb the methylene blue (MB) dye from other organic dyes.

Tuning the intermolecular interaction of A 2 -A 1 -D-A 1 -A 2 type non-fullerene acceptors by substituent engineering for organic solar cells with ultrahigh V OC of ~1.2 V

Abstract: For non-fullerene acceptors (NFAs) with linear A2-A1-D-A1-A2 backbone, there are three kinds of possible intermolecular interaction, A1-A1, A1-A2 and A2-A2 stacking. Hence, it is a huge challenge to control this interaction and investigate the effect of intermolecular stacking model on the photovoltaic performance. Here, we adopt a feasible strategy, by utilizing different substituent groups on terminal A2 unit of dicyanomethylene rhodanine (RCN), to modulate this stacking model. According to theoretical calculation results, the molecule BTA3 with ethyl substituent packs via heterogeneous interaction between A2 and A1 unit in neighboring molecules. Surprisingly, the benzyl group can effectively transform the aggregation of BTA5 into homogeneous packing of A2-A2 model, which might be driven by the strong interaction between benzyl and A1 (benzotriazole) unit. However, different with benzyl, phenyl end group impedes the intermolecular interaction of BTA4 due to the large steric hindrance. When using a BTA-based D-π-A polymer J52-F as donor according to “Same-A-Strategy”, BTA3-5 could achieve ultrahigh open-circuit voltage ( V OC) of 1.17–1.21 V. Finally, BTA5 with benzyl groups realized an improved power conversion efficiency (PCE) of 11.27%, obviously higher than that of BTA3 (PCE=9.04%) and BTA4 (PCE=5.61%). It is also worth noting that the same trend can be found when using other four classic p-type polymers of P3HT, PTB7, PTB7-Th and PBDB-T. This work not only investigates the intermolecular interaction of A2-A1-D-A1-A2 type NFAs for the first time, but also provides a straightforward and universal method to change the interaction model and improve the photovoltaic performance.

Substituent effect of conjugated microporous polymers on the photocatalytic hydrogen evolution activity

Abstract: The construction of a donor–acceptor (D–A) organic photocatalyst is a facile approach to improve photocatalytic performances because of the efficient separation of light-generated electrons and holes. The rational design of molecular skeletons and the selection of functional groups are of great importance to an organic photocatalyst with a high photocatalytic activity. Herein, we designed two D–A conjugated microporous polymers (CMPs) with different substituent groups of fluorine atoms and methyl groups on the acceptor unit of dibenzothiophene-dioxide (DBTDO). This study reveals that the introduction of fluorine atoms with strong electron-withdrawing ability onto the acceptor unit can further enhance the electron acceptability of the DBTDO unit, leading to the efficient separation of light-generated electrons and holes, while the introduction of methyl with electron-pushing ability decreases the electron acceptability of the acceptor unit, suppressing the separation of light-generated charge carriers. As a result, the polymer PyDF with fluorine atoms shows an excellent photocatalytic activity compared to PyDM with methyl groups. Under UV/Vis light irradiation, PyDF shows an attractive photocatalytic hydrogen generation rate of 18.93 mmol h−1 g−1, which is much higher than that of PyDM (3.96 mmol h−1 g−1), implying that the functional group acts as a vital role in the catalytic activity of polymer semiconducting photocatalysts.

A Triazole-Substituted Aryl Iodide with Omnipotent Reactivity in Enantioselective Oxidations.

Abstract: A widely applicable triazole-substituted chiral aryl iodide is described as catalyst for enantioselective oxidation reactions. The introduction of a substituent in ortho-position to the iodide is key for its high reactivity and selectivity. Besides a robust and modular synthesis, the main advantage of this catalyst is the excellent performance in a plethora of mechanistically diverse enantioselective transformations, such as spirocyclizations, phenol dearomatizations, α-oxygenations, and oxidative rearrangements. DFT-calculations of in situ generated [hydroxy(tosyloxy)iodo]arene isomers give an initial rational for the observed reactivity.

Photoredox Catalytic α-Alkoxypentafluorosulfanylation of α-Methyl- and α-Phenylstyrene Using SF6.

Abstract: SF6 was applied as pentafluorosulfanylation reagent to prepare ethers with a vicinal SF5 substituent through a one-step method involving photoredox catalysis. This method shows a broad substrate scope with respect to applicable alcohols for the conversion of α-methyl and α-phenyl styrenes. The products bear a new structural motif with two functional groups installed in one step. The alkoxy group allows elimination and azidation as further transformations into valuable pentafluorosulfanylated compounds. These results confirm that non-toxic SF6 is a useful SF5 transfer reagent if properly activated by photoredox catalysis, and toxic reagents are completely avoided. In combination with light as an energy source, a high level of sustainability is achieved. Through this method, the proposed potential of the SF5 substituent in medicinal chemistry, agrochemistry, and materials chemistry may be exploited in the future.

Ruthenium(II) Complexes of Heteroditopic N-Heterocyclic Carbene Ligands: Efficient Catalysts for C-N Bond Formation via a Hydrogen-Borrowing Strategy under Solvent-Free Conditions.

Abstract: Both imidazol-2-ylidene (ImNHC) and 1,2,3-triazol-5-ylidene (tzNHC) have evolved to be elite groups of N-heterocyclic carbene (NHC) ligands for homogeneous catalysis. To develop efficient ruthenium(II)-based catalysts incorporating these ligands for C-N bond-forming reactions via hydrogen-borrowing methodology, we utilized chelating ligands integrated with ImNHC and mesoionic tzNHC donors connected via a CH2 spacer with a diverse triazole backbone. The synthesized ruthenium(II) complexes 3 are found to be highly efficient for C-N bond formation across a wide range of primary amine and alcohol substrates under solvent-free conditions, and among all of the complexes studied here, catalyst 3a with a mesityl substituent displayed maximum activity. To our delight, catalyst 3a is also effective for the selective mono-N-methylation of various anilines utilizing methanol as a coupling partner, known to be relatively more difficult than other alcohols. Furthermore, complex 3a also delivers various substituted quinolines successfully via the reaction of 2-aminobenzyl alcohol with several secondary alcohols. Importantly, catalyst 3a exhibited the highest activity among the reported ruthenium(II) complexes for both the N-benzylation of aniline [achieving a turnover number (TON) of 50000] and the realization of quinoline 8a by reacting 2-aminobenzyl alcohol with 2-phenylethanol (attaining a TON of 30000).

New wide-stability four-ring azo/ester/Schiff base liquid crystals: synthesis, mesomorphic, photophysical, and DFT approaches

Abstract: New four-groups-based azo/ester/Schiff base liquid crystals, ((4-substitutedphenylimino)methyl)phenyl 4-[2-(4-alkoxyhenyl)diazenyl]benzoate, Ina–d, were synthesized and analyzed for their mesomorphic stability and optical activity. In these compounds, a terminal alkoxy group of variable chain length from n = 6 to n = 16 carbons is attached to the end of a phenylazo benzoate moiety and the other end of the molecules is connected to a different polar compact substituent X (CH3O, CH3, H, and Cl). FT-IR, 1H NMR, mass spectroscopy and elemental analysis were carried out for molecular structure confirmation of the prepared compounds. The mesomorphic properties were confirmed using a combination of differential scanning calorimetry (DSC) and polarized light microscopy (PLM). The photophysical property was studied by UV-vis spectroscopy. All the prepared homologous series exhibited high thermal stability with a wide-temperature mesomorphic range. The thermal and geometrical parameters of the investigated compounds were estimated by density functional theory (DFT). The results revealed that all the compounds were not completely planar with a relatively high twisting moiety at the CHN part and their twist angles were affected by the electronic nature of the attached X group. Moreover, the calculated quantum chemical parameters as determined by the DFT approach of the investigated compounds were related to the experimentally determined values of the mesophase thermal stability (Tc) and mesophase temperature ranges (ΔTSmA and ΔTN) as well as the type of the mesophase.

Monocomponent Photoinitiators based on Benzophenone-Carbazole Structure for LED Photoinitiating Systems and Application on 3D Printing.

Abstract: In this article, different substituents (benzoyl, acetyl, styryl) are introduced onto the carbazole scaffold to obtain 8 novel carbazole derivatives. Interestingly, a benzoyl substituent, connected to a carbazole group, could form a benzophenone moiety, which composes a monocomponent Type II benzophenone-carbazole photoinitiator (PI). The synergetic effect of the benzophenone moiety and the amine in the carbazole moiety is expected to produce high performance photoinitiating systems (PISs) for the free radical photopolymerization (FRP). For different substituents, clear effects on the light absorption properties are demonstrated using UV-Visible absorption spectroscopy. Benzophenone-carbazole PIs can initiate the FRP of acrylates alone (monocomponent Type II photoinitiator behavior). In addition, fast polymerization rates and high function conversions of acrylate are observed when an amine and/or an iodonium salt are added in systems. Benzophenone-carbazole PIs have good efficiencies in cationic photopolymerization (CP) upon LED @ 365 nm irradiation in the presence of iodonium salt. In contrast, other PIs without synergetic effect demonstrate unsatisfied photopolymerization profiles in the same conditions. The best PIS identified for the free radical photopolymerization were used in three-dimensional (3D) printing. Steady state photolysis and fluorescence quenching experiments were carried out to investigate the reactivity and the photochemistry and photophysical properties of PIs. The free radicals, generated from the studied PISs, are detected by the electron spin resonance - spin trapping technique. The proposed chemical mechanisms are provided and the structure/reactivity/efficiency relationships are also discussed. All the results showed that the benzophenone-carbazole PIs have a good application potential, and this work provides a rational design route for PI molecules. Remarkably, BPC2-BPC4, C6, C8 were never synthetized before; therefore, 5 of the 8 compounds are completely new.

Intermolecular electronic coupling of 9-methyl-9H-dibenzo[a,[c] carbazole for strong emission in aggregated state by substituent effect

Abstract: Bright emission of organic luminogens at aggregated state has attracted increasing attention for their potential applications in opto-electronic devices and bio-/chemo-sensors. In this article, upon the introduction of different substituents (Br, Ph and TPh) to the large conjugated core of 9-methyl-9 H -dibenzo[ a , c ]carbazole (DBC) moiety, the resultant luminogens demonstrated PL quantum yields in solid state ranging from 4.81% to 47.39%. Through the systematic investigation of molecular packing, together with theory calculation, the strong intermolecular electronic coupling in the dimers is proved as the main factor to the bright emission in the solid state. The results afforded a new avenue to investigate the intrinsic relationship among the molecular structures, packing modes and emission properties.

Molecular Bismuth Cations: Assessment of Soft Lewis Acidity.

Abstract: Three‐coordinate cationic bismuth compounds [Bi(diaryl)(EPMe\(_{3}\))][SbF\(_{6}\)] have been isolated and fully characterized (diaryl=[(C\(_{6}\)H\(_{4}\))\(_{2}\)C\(_{2}\)H\(_{1}\)]\(^{2-}\), E=S, Se). They represent rare examples of molecular complexes with Bi⋅⋅⋅EPR\(_{3}\) interactions (R=monoanionic substituent). The \(^{31}\)P NMR chemical shift of EPMe3 has been found to be sensitive to the formation of LA⋅⋅⋅EPMe\(_{3}\) Lewis acid/base interactions (LA=Lewis acid). This corresponds to a modification of the Gutmann–Beckett method and reveals information about the hardness/softness of the Lewis acid under investigation. A series of organobismuth compounds, bismuth halides, and cationic bismuth species have been investigated with this approach and compared to traditional group 13 and cationic group 14 Lewis acids. Especially cationic bismuth species have been shown to be potent soft Lewis acids that may prefer Lewis pair formation with a soft (S/Se‐based) rather than a hard (O/N‐based) donor. Analytical techniques applied in this work include (heteronuclear) NMR spectroscopy, single‐crystal X‐ray diffraction analysis, and DFT calculations.

Chiral Phosphoric Acid Dual-Function Catalysis: Asymmetric Allylation with α-Vinyl Allylboron Reagents.

Abstract: We report a dual function asymmetric catalysis by a chiral phosphoric acid catalyst that controls both enantioselective addition of an achiral α-vinyl allylboronate to aldehydes and pseudo-axial orientation of the α-vinyl group in the transition state. The reaction produces dienyl homoallylic alcohols with high Z-selectivities and enantioselectivities. Computational studies revealed that minimization of steric interactions between the alkyl groups of the diol on boron and the chiral phosphoric acid catalyst influence the orientation of α-vinyl substituent of the allylboronate reagent to occupy a pseudo-axial position in the transition state.

Arene C−H Activation at Aluminium(I): meta Selectivity Driven by the Electronics of SNAr Chemistry

Abstract: The reactivity of the electron-rich anionic Al(I) ('aluminyl') compound K 2 [(NON)Al] 2 (NON = 4,5-bis(2,6-diisopropylanilido)-2,7-di- tert -butyl-9,9-dimethylxanthene) towards mono- and disubstituted arenes is reported. C-H activation chemistry with n -butylbenzene gives exclusively the product of activation at the arene meta position. Mechanistically, this transformation proceeds in a single step via a concerted Meisenheimer-type transition state. Selectivity is therefore based on similar electronic factors to classical S N Ar chemistry, which implies the destabilization of transition states featuring electron-donating groups in either the ortho or the para positions. In the cases of toluene and the three isomers of xylene, benzylic C-H activation is also possible, with the product(s) formed reflecting the feasibility (or otherwise) of competing arene C-H activation at a site which is neither ortho or para to a methyl substituent.

Organic Solar Cells Based on Non-fullerene Small-Molecule Acceptors: Impact of Substituent Position

Abstract: Summary Molecular engineering of non-fullerene small-molecule acceptors (SMAs) plays a key role in enhancing the performance of organic solar cells. An effective strategy is to introduce functional groups into SMA end groups to tune the electronic and morphological properties of polymer/SMA blends. Here, molecular dynamics simulations and long-range corrected density functional theory calculations are combined to examine the impact of the position of methoxy substitution in the SMA end groups. As representative systems, blends of the IT-OM small-molecule acceptor with the PBDB-T polymer donor are explored; three different positions of the methoxy substitution of the IT-OM end groups are examined. By considering intermolecular mixing and packing, the energetic distribution of the charge-transfer electronic states, the exciton-dissociation and non-radiative recombination processes, and the electron-transfer rates among adjacent acceptors, we provide a comprehensive molecular-scale rationalization of the significant experimental variations in device performance for PBDB-T/IT-OM-based solar cells as a function of methoxy position.

Remote Perfluoroalkyl Substituents are Key to Living Aqueous Ethylene Polymerization

Abstract: In various nickel(II) salicylaldiminato ethylene polymerization catalysts, which are a versatile mechanistic probe for substituent effects, longer perfluoroalkyl groups exert a strong effect on catalytic activities and polymer microstructures compared to the trifluoromethyl group. This effect is accounted for by a reduced electron density on the active sites, and is also supported by electrochemical studies. Thus, β-hydride elimination, the key step of chain transfer and branching pathways, is disfavored while chain-growth rates are enhanced. This enhancement occurs to an extent that enables living polymerizations in aqueous systems to afford ultra-high-molecular-weight polyethylene for various chelating salicylaldimine motifs. These findings are mechanistically instructive as well as practically useful for illustrating the potential of perfluoroalkyl groups in catalyst design.

A General Strategy to Enhance Donor-Acceptor Molecules Using Solvent-Excluding Substituents.

Abstract: While organic donor-acceptor (D-A) molecules are widely employed in multiple areas, the application of more D-A molecules could be limited because of an inherent polarity sensitivity that inhibits photochemical processes. Presented here is a facile chemical modification to attenuate solvent-dependent mechanisms of excited-state quenching through addition of a β-carbonyl-based polar substituent. The results reveal a mechanism wherein the β-carbonyl substituent creates a structural buffer between the donor and the surrounding solvent. Through computational and experimental analyses, it is demonstrated that the β-carbonyl simultaneously attenuates two distinct solvent-dependent quenching mechanisms. Using the β-carbonyl substituent, improvements in the photophysical properties of commonly used D-A fluorophores and their enhanced performance in biological imaging are shown.

Substituent Effect on Triplet State Aromaticity of Benzene.

Abstract: Density functional theory calculations have been performed to explore the substituent effect on benzene's structure and aromaticity upon excitation to the first triplet excited state (T1). Discussion is based on spin density analysis, HOMA (harmonic oscillator model of aromaticity), NICS (nucleus-independent chemical shift), ACID (anisotropy of the induced current density), and monohydrogenation free energies and shows that a large span of aromatic properties, from highly antiaromatic to strongly aromatic, could be achieved by varying the substituent. This opens up a possibility of controlling benzene's physicochemical behavior in its excited state, while molecular motion, predicted for several derivatives, could be of interest for the development of photomechanical materials.

The interplay of conformations and electronic properties in N -aryl phenothiazines

Abstract: A broad series of electronically diverse N-aryl substituted phenothiazines was readily synthesized by Buchwald–Hartwig amination of 10H-phenothiazine and aryl bromides with variable electronic nature in moderate to excellent yields (61–97%). This library of N-aryl phenothiazines was studied with respect to their electronic properties by absorption and emission spectroscopy, cyclic voltammetry, and quantum chemical calculations to elucidate the electronic structure. Furthermore, DFT calculations allow assigning substituent dependent dominance of intra or extra conformations by virtue of the electronic nature of the remote N-aryl substituent. Electron releasing substituents favor intra and electron withdrawing substituents favor extra conformations in the electronic ground state. The experimentally determined oxidation potentials as well as the calculated molecular geometries strongly correlate with Hammett σp parameters of the remote para-substituents. Therefore, transmission of the substituent effect operates by both resonance and inductive mechanisms. This linear correlation equation can be applied to assign new sigma parameters σp for several substituents on the basis of the experimentally determined oxidation potentials.

Towards the Molecular Design of Spin-Crossover Complexes of 2,6-Bis(pyrazol-3-yl)pyridines.

Abstract: The molecular design of spin-crossover complexes relies on controlling the spin state of a transition metal ion by proper chemical modifications of the ligands. Herein, the first N,N'-disubstituted 2,6-bis(pyrazol-3-yl)pyridines (3-bpp) are reported that, against the common wisdom, induce a spin-crossover in otherwise high-spin iron(II) complexes by increasing the steric demand of a bulky substituent, an ortho-functionalized phenyl group. As N,N'-disubstituted 3-bpp complexes have no pendant NH groups that make their spin state extremely sensitive to the environment, the proposed ligand design, which may be applicable to isomeric 1-bpp or other families of popular bi-, tri- and higher denticity ligands, opens the way for their molecular design as spin-crossover compounds for future breakthrough applications.

The substituent guest effect on four-step spin-crossover behavior

Abstract: Until now, the synthesis of new multi-step spin-crossover (SCO) materials is still a great challenge although they have attracted significant attention due to their potential applications in high-order data storage and multi-switches. Here, based on the four-step SCO complex [Fe(dpoda){Ag(CN)2}2]·1.5naph (1·1.5naph, dpoda = 2,5-di-(pyridyl)-1,3,4-oxadiazole, naph = naphthalene), the strategy of incorporating a substituent on an aromatic guest is applied. Since the replacement of H with an F atom can be regarded as isosteric substitution, the introduction of the 2-fluoronaphthalene (Fnaph) guest does not give rise to large structural changes and the four-step SCO behavior is maintained in 1·1.5Fnaph; however, fine-tuning of the framework is indeed achieved by the fluoro substituent. The spin transition temperatures of 1·1.5Fnaph shift to the low-temperature region, which should be due to the contributions of the size effect and the decrease in the Fe–NC angle. Meanwhile, the thermal hysteresis loop disappears, which results from the competitive contributions of the π⋯π and F⋯Ag interactions. Therefore, the F substituent on the guest can effectively modify the four-step SCO behavior, which provides a simple solution to synthesize more multi-step SCO materials.

Enhancing Chain Initiation Efficiency in the Cationic Allyl-Nickel Catalyzed (Co)Polymerization of Ethylene and Methyl Acrylate

Abstract: Improving the efficiency of chain initiation is highly important and also highly challenging in the development of olefin polymerization catalysts. A series of 2-methylallyl-based nickel complexes supported by aryl-N-bridged diphosphazane monoxide (PNPO) ligands containing different electronic and steric substituents were prepared and characterized. These nickel complexes are highly active single-component catalysts for ethylene polymerization and copolymerization with methyl acrylate (MA). 2-Methylallyl substituent on the μ-allyl catalysts led to an increase in the efficiency of chain initiation compared with the corresponding allyl-based analogues, improving the catalytic performances with high activity (up to 4.02 × 106 g PE (mol Ni)-1 h-1). Linear polyethylenes with high molecular weight, narrow PDI values, and high melting temperatures were generated. Most importantly, these 2-methylallyl nickel catalysts can promote ethylene-MA copolymerization to afford functionalized polyethylenes with MA incorporation of up to 7.0 mol %. The current work demonstrates that the change of initiating units can lead to enhancement in catalyst performances. This provides an alternative, simple, and potentially general strategy to improve the properties of different catalyst systems.

Influence of Substituent Groups on Chemical Reactivity Kinetics of Nonfullerene Acceptors

Abstract: Substitution (such as fluorine substitution, F) of terminal groups or atoms in nonfullerene acceptors (NFAs) is an effective strategy to tune the optoelectronic properties of nonfullerene electron ...

Preorganization: A Powerful Tool in Intermolecular Halogen Bonding in Solution.

Abstract: Preorganization is a powerful tool in supramolecular chemistry which has been utilized successfully in intra- and intermolecular halogen bonding. In previous work, we had developed a bidentate bis(iodobenzimidazolium)-based halogen bond donor which featured a central trifluoromethyl substituent. This compound showed a markedly increased catalytic activity compared to unsubstituted bis(iodoimidazolium)-based Lewis acids, which could be explained either by electronic effects (the electron withdrawal by the fluorinated substituent) or by preorganization (the hindered rotation of the halogen bonding moieties). Herein, we systematically investigate the origin of this increased Lewis acidity via a comparison of the two types of compounds and their respective derivatives with or without the central trifluoromethyl group. Calorimetric measurements of halide complexations indicated that preorganization is the main reason for the higher halogen bonding strength. The performance of the catalysts in a series of benchmark reactions corroborates this finding.