Long‐range corrected functionals satisfy Koopmans' theorem: Calculation of correlation and relaxation energies

In this article, we show that the long‐range‐corrected (LC) density functionals LC‐BOP and LCgau‐BOP reproduce frontier orbital energies and highest‐occupied molecular orbital (HOMO)—lowest‐unoccupied molecular orbital (LUMO) gaps better than other density functionals. The negative of HOMO and LUMO energies are compared with the vertical ionization potentials (IPs) and electron affinities, respectively, using CCSD(T)/6‐311++G(3df,3pd) for 113 molecules, and we found LC functionals to satisfy Koopmans' theorem. We also report that the frontier orbital energies and the HOMO‐LUMO gaps of LC‐BOP and LCgau‐BOP are better than those of recently proposed ωM05‐D (Lin et al., J. Chem. Phys. 2012, 136 , 154109). We express the exact IP in terms of orbital relaxation, and correlation energies and hence calculate the relaxation and correlation energies for the same set of molecules. It is found that the LC functionals, in general, includes more relaxation effect than Hartree–Fock and more correlation effect than the other density functionals without LC scheme. Finally, we scan μ parameter in LC scheme from 0.1 to 0.6 bohr^?1 for the above test set molecules with LC‐BOP functional and found our parameter value, 0.47 bohr^?1, is usefully applicable to our tested systems. © 2013 Wiley Periodicals, Inc.     

Effects of different basis sets and donor‐acceptor groups on linear and second‐order nonlinear optical properties and molecular frontier orbital energies

The calculation of molecular hyperpolarizability, molecular frontier orbital energies of some donor‐acceptor oxadiazoles ( 5a – f , 8a – f , and 9a – f ) have been investigated using ab initio methods and different basis sets. Ab initio optimizations were performed at the Hartree–Fock (HF) and density functional (Beckee‐3–Lee–Yang–Parr; B3LYP) levels of theory with 6‐31G basis set. The polarizability (<α>), anisotropy of polarizability (Δα), and ground‐state dipole moment (μ), first hyperpolarizability (β), and molecular frontier orbital (HOMO, highest occupied molecular orbital and LUMO, lowest unoccupied molecular orbital) energies of 5a – f , 8a – f , and 9a – f have been calculated at the HF and B3LYP methods with 6‐31G, 6‐31G(d), 6‐31+G(d), 6‐31++G(d,p), 6‐311G, 6‐311G(d), 6‐311+G(d), and 6‐311++G(d,p) basis sets. Also, the molecular hardness (η) and electronegativity (χ) parameters have been obtained using molecular frontier orbital energies. The <α>, Δα, μ, β, HOMO, LUMO energies, η and χ parameters have been investigated as dependence on the choice of method and basis set. The variation graphics of <α>, Δα, μ, β, η, and χ parameters using HF and B3LYP methods with different basis sets are presented. We have examined the frontier molecular orbital pictures of 5a – f , 8a – f , and 9a – f using B3LYP/6‐31++G(d,p) level. The 5a – f , 8a – f , and 9a – f display significant linear, second‐order molecular nonlinearity, and molecular parameters and provide the basis for future design of efficient nonlinear optical materials having the 1,3,4‐oxadiazole core. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Convergent Modulation of Singlet and Triplet Excited States of Phosphine‐Oxide Hosts through the Management of Molecular Structure and Functional‐Group Linkages for Low‐Voltage‐Driven Electrophosphorescence

The controllable tuning of the excited states in a series of phosphine‐oxide hosts ( DPExPOCzn ) was realized through introducing carbazolyl and diphenylphosphine‐oxide (DPPO) moieties to adjust the frontier molecular orbitals, molecular rigidity, and the location of the triplet excited states by suppressing the intramolecular interplay of the combined multi‐insulating and meso linkage. On increasing the number of substituents, simultaneous lowering of the first singlet energy levels (S₁) and raising of the first triplet energy levels (T₁, about 3.0 eV) were achieved. The former change was mainly due to the contribution of the carbazolyl group to the HOMOs and the extended conjugation. The latter change was due to an enhanced molecular rigidity and the shift of the T₁ states from the diphenylether group to the carbazolyl moieties. This kind of convergent modulation of excited states not only facilitates the exothermic energy transfer to the dopants in phosphorescent organic light‐emitting diodes (PHOLEDs), but also realizes the fine‐tuning of electrical properties to achieve the balanced carrier injection and transportation in the emitting layers. As the result, the favorable performance of blue‐light‐emitting PHOLEDs was demonstrated, including much‐lower driving voltages of 2.6 V for onset and 3.0 V at 100 cd m^?2, as well as a remarkably improved E.Q.E. of 12.6 %.     

The effect of conjugated spacer on novel carbazole derivatives for dye‐sensitized solar cells: Density functional theory/time‐dependent density functional theory study

The ground‐state structure and frontier molecular orbital of D‐π‐A organic dyes, CFT1A, CFT2A, and CFT1PA were theoretically investigated using density functional theory (DFT) on B3LYP functional with 6‐31G(d,p) basis set. The vertical excitation energies and absorption spectra were obtained using time‐dependent DFT (TD‐DFT). The adsorptions of these dyes on TiO₂ anatase (101) were carried out by using a 38[TiO₂] cluster model using Perdew–Burke–Ernzerhof functional with the double numerical basis set with polarization (DNP). The results showed that the introduction of thiophene–thiophene unit (T–T) as conjugated spacer in CFT2A could affect the performance of intramolecular charge transfer significantly due to the inter‐ring torsion of T–T being decreased compared with phenylene–phenylene (P–P) spacer of CFP2A in the researhcers' previous report. It was also found that increasing the number of π‐conjugated unit gradually enhanced charge separation between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of these dyes, leading to a high‐efficiency photocurrent generation. The HOMO–LUMO energy gaps were calculated to be 2.51, 2.37, and 2.50 eV for CFT1A, CFT2A, and CFT1PA respectively. Moreover, the calculated adsorption energies of these dyes on TiO₂ cluster were ～14 kcal/mol, implying that these dyes strongly bind to TiO₂ surface. Furthermore, the electronic HOMO and LUMO shapes of all dye–TiO₂ complexes exhibited injection mechanism of electron via intermolecular charge‐transfer transition. © 2012 Wiley Periodicals, Inc.     

Synthesis,structural analysis,spectral investigations,and DFT calculations of 1‐(3‐amino‐4‐thia‐1,2‐diazaspiro[4.11]hexadec‐2‐en‐1‐yl)ethan‐1‐one

1‐(3‐amino‐4‐thia‐1,2‐diazaspiro[4.11]hexadec‐2‐en‐1‐yl)ethan‐1‐one was synthesized and experimentally characterized by using FT‐IR, ¹H NMR, ¹³C NMR, and UV–Vis spectroscopy. The structure of the compound was confirmed by single‐crystal X‐ray diffraction. In the crystal structure, the molecules are linked by pairs of N‐H⋯N hydrogen bonds, forming centrosymmetric dimers with the graph‐set motif. The water molecule also plays an important role in the stabilization of the crystal structure, bridging the dimers to form a two‐dimensional supramolecular network. The molecular geometry, frontier molecular orbitals, vibrational frequencies, electronic properties, and molecular electrostatic potential were calculated using density functional theory (DFT) with the B3LYP/6‐311G(d,p) basis set. Geometric parameters, vibrational assignments, and electronic properties such as calculated energies, excitation energies, and oscillator strengths were compared with the experimental data, and it was seen that the theoretical results support the experimental parameters.     

DFT/TDDFT Studies on the Electronic Structures and Spectral Properties of Carbazole‐based Blue Light‐emitting Dendrimers

The purpose of this paper is to provide an in‐depth investigation of the electronic and optical properties of two series of carbazole‐based blue light‐emitting dendrimers, including 1 – 6 six oligomers. These materials show great potential for application in organic light‐emitting diodes as efficient blue‐light and red‐light emitting materials due to the tuning of the optical and electronic properties by the use of different electron donors (D) and electron acceptors (A). The geometric and electronic structures of these compounds in the ground state are calculated using density functional theory (DFT) and the ab initio HF, whereas the lowest singlet excited states were optimized by ab initio single excitation configuration interaction (CIS). All DFT calculations are performed using the B3LYP functional on 6‐31G* basis set. The outcomes show that the highest occupied molecular orbitals (HOMOs), lowest occupied molecular orbitals (LUMOs), energies gaps, ionization potentials, electron affinities and reorganization energies of each molecular are affected by different D and A moieties and different substitute positions.     

Density functional study on electronic structures and reactivity in methyl‐substituted chelates used in organic light‐emitting diodes

The electronic structure and reactivity trends of a set of tris‐(n‐methyl‐8‐quinolinolato) metal (III) (n = 0, 3, 4, 5; metal = Al⁺³, Ga⁺³) used as electron‐transport layer in organic light‐emitting diodes were studied and compared. All geometries were optimized at B3LYP/6‐31G(d,p) level of theory. The geometries of the ground state (S₀) of unsubstituted molecules AlQ3 and GaQ3 were found to be slightly affected by the methyl group, which is in agreement with previous works. Methyl‐derivatives conserve largely the electronic structures of AlQ3 and GaQ3. The energies of the frontier orbitals highest occupied and lowest unoccupied molecular orbital are raised by the electron‐releasing effect of methyl group. Molecular orbital contribution analysis reveals that the orbital population is essentially the same for both MQ3 and their derivatives. Analyses of the ionization potential and electron affinity showed that MQ3 tend to be better hole‐blockers than methylated analogues and 5Me‐MQ3 have higher hole‐injection capability than the other methyl‐substituted derivatives. The global reactivity analysis showed that the electrophilicity index can be an indicator of electron‐injection capability in these complexes. Local reactivity analysis showed that atomic sites that are prone to nucleophilic/electrophilic attack are atoms C‐4 in L3/C‐5 in L1. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Moving toward Ylide‐Stabilized Carbenes

The effect of ylide substitution at the α position to the carbene carbon (C_c) atom on the stability and σ‐donating ability of a number of cyclic carbenes has been studied theoretically. The stabilities of all of the carbenes were investigated from an evaluation of their singlet–triplet energy gaps and stabilization energies. All carbenes were found to have a stable singlet state. The energy of the σ‐symmetric lone‐pair orbital at the C_c atom increases as a result of the introduction of ylide centers near to the C_c atom. This indicates an enhanced σ‐donating ability of the ylide‐containing carbenes. The calculated carbonyl‐stretching frequencies of the corresponding rhodium complexes, proton affinities, and nucleophilicity index values correlate well with the σ basicity of the carbenes.     

Synthesis and electro‐optical properties of polyfluorene modified with randomly distributed electron‐donor and rotaxane electron‐acceptor structural units in the main chain

Polyfluorene PF?γCD rotaxane copolymer, composed of randomly distributed 9,9‐dioctylfluorene, methyltriphenylamine (electron‐donating) and 9‐dicyanomethylenefluorene complexed with γ‐cyclodextrin (γCD) (electron‐accepting) structural units, has been synthesized by Suzuki cross‐coupling reaction. The chemical structures were proved by FTIR and ¹H NMR spectroscopy. The surface morphology, thermal, optical, electrochemical behavior, and adhesion characteristics of the obtained rotaxane copolymer have been investigated and compared with those of the nonrotaxane counterpart ( PF ). Relatively high fluorescence efficiency, almost identical normalized absorbance maximum in solution and solid‐state of PF?γCD rotaxane copolymer, and a more uniform and smoother surface with lower adhesion forces provides the role of γCD encapsulation on the lower aggregation propensity. PF?γCD and PF copolymers exhibit n‐ and p‐doping processes and blue‐light emission in the film state. The optical and electrochemical band gaps (ΔE_g), as well as the highest occupied molecular orbital/lowest unoccupied molecular orbital positions in an energetic diagram indicate that both copolymers are promising blue‐emitting electroluminescent materials. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Phosphorescence Color Tuning by Ligand,and Substituent Effects of Multifunctional Iridium(III) Cyclometalates with 9‐Arylcarbazole Moieties

The synthesis, isomeric studies, and photophysical characterization of a series of multifunctional cyclometalated iridium(III) complexes containing a fluoro‐ or methyl‐substituted 2‐[3‐(N‐phenylcarbazolyl)]pyridine molecular framework are presented. All of the complexes are thermally stable solids and highly efficient electrophosphors. The optical, electrochemical, photo‐, and electrophosphorescence traits of these iridium phosphors have been studied in terms of the electronic nature and coordinating site of the aryl or pyridyl ring substituents. The correlation between the functional properties of these phosphors and the results of density functional theory calculations was made. Arising from the propensity of the electron‐rich carbazolyl group to facilitate hole injection/transport, the presence of such a moiety can increase the highest‐occupied molecular orbital levels and improve the charge balance in the resulting complexes relative to the parent phosphor with 2‐phenylpyridine ligands. Remarkably, the excited‐state properties can be manipulated through ligand and substituent effects that allow the tuning of phosphorescence energies from bluish green to deep red. Electrophosphorescent organic light‐emitting diodes (OLEDs) with outstanding device performance can be fabricated based on these materials, which show a maximum current efficiency of approximately 43.4 cd A^?1, corresponding to an external quantum efficiency of approximately 12.9 % ph/el (photons per electron) and a power efficiency of approximately 33.4 Lm W^?1 for the best device. The present work provides a new avenue for the rational design of multifunctional iridium–carbazolyl electrophosphors, by synthetically tailoring the carbazolyl pyridine ring that can reveal a superior device performance coupled with good color‐tuning versatility, suitable for multicolor‐display technology.     

Density functional theory study of a molecular allosteric switch for 2,2′‐bipyridyl‐3,3′‐15‐crown‐5

A classical model of “molecular machine,” which acts as an ON–OFF switch for 2,2′‐bipyridyl‐3,3′‐15‐crown‐5 ( L ), has been theoretically studied. It is highly important to understand the mechanism of this switch. The alkali‐metal cations (Na⁺ and K⁺) and W(CO)₄ fragment are introduced to coordinate with the different active sites of L , respectively. The density functional theory (DFT) method is used for understanding the stereochemical structural natures and thermodynamic properties of all the target molecules at B3LYP/6‐31G(d) and SDD (Stuttgart–Dresden) level, together with the corresponding effective core potential (ECP) for tungsten (W). The fully optimized geometries have been performed with real frequencies, which indicate the minima states. The nucleophilicity of L has been investigated by the Fukui functions. The natural bond orbital analysis is used to study the intermolecular charge‐transfer interactions and explore the origin of the internal forces of the molecular switch. In addition, the binding energies, enthalpies, Gibbs free energies, and the cation exchange energies have been studied for L , W(CO)₄ L , and their corresponding complexes. The properties of the complexes displayed by in presence or absence of the W(CO)₄ fragment are also analyzed. The calculated results of allosterism displayed by L are in a good agreement with the experimental results. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2011     

An Insight of the Results Provided by Color‐Tuning Studies Made on Ir(III) Complexes: A pi‐Neutral CF3 Group Viewed by Adjusting Energies of pi‐type Molecular Orbitals

The pi‐nature of a CF₃ group can be understood through analysis of its bond orbitals (BOs) mixed into the pi‐type molecular orbitals of CF₃‐substituted Ir(ppy)₂MDPA⁺ complexes (ppy=2‐phenyl‐pyridine and MDPA=methylated 2,2′‐dipyridyl amine). It has been found that, through this natural bond orbital analysis, the parent’s molecular orbitals (MOs) can be stabilized by χρ^*_CF BO via negative hyperconjugation and, simultaneously, destabilized by electron lp(F) BO. Since these two competing pi‐effects are virtually counterbalanced as indicated by the vanishing values of crystal orbital overlap populations, the chemical substitution strategy originated from lowering of HOMO by using this electron‐withdrawing CF₃ group has been found effective in color‐tuning to blue region. Based on reduced shielding effect due to de‐ creased χρ‐electron density, the reported position dependent CF₃‐substitution effects on pi‐type MOs can also be understood through HOMO/LUMO wavefunction analysis.     

Core‐and‐Surface‐Functionalized Polyphenylene Dendrimers for Solution‐Processed,Pure‐Blue Light‐Emitting Diodes Through Surface‐to‐Core Energy Transfer

Several pyrene‐based polyphenylene dendrimers (PYPPDs) with different peripheral chromophores (PCs) are synthesized and characterized. Deep blue emissions solely from the core are observed for all of them in photoluminescence spectra due to good steric shielding of the core and highly efficient surface‐to‐core Förster resonant energy transfers (FRETs). Device performances are found in good correlation with the energy gaps between the work function of the electrodes and the frontier molecular orbital (FMO) levels of the PCs. Pure blue emission, luminance as high as 3700 cd m⁻² with Commission Internationale de l'Éclairage 1931 (CIE_xy) = (0.16, 0.21), and a peak current efficiency of 0.52 cd A⁻¹ at CIE_xy = (0.17, 0.20) are achieved. These dendrimers are among the best dendritic systems so far for fluorescent blue light‐emitting materials.

     

Basis set effects on frontier molecular orbital energies and energy gaps: a comparative study between plane waves and localized basis functions in molecular systems

In order to study the Kohn-Sham frontier molecular orbital energies in the complete basis limit, a comparative study between localized functions and plane waves, obtained with the local density approximation exchange-correlation functional is made. The analyzed systems are ethylene and butadiene, since they are theoretical and experimentally well characterized. The localized basis sets used are those developed by Dunning. For the plane-waves method, the pseudopotential approximation is employed. The results obtained by the localized basis sets suggest that it is possible to get an estimation of the orbital energies in the limit of the complete basis set, when the basis set size is large. It is shown that the frontier molecular orbital energies and the energy gaps obtained with plane waves are similar to those obtained with a large localized basis set, when the size of the supercell and the plane-wave expansion have been appropriately calibrated.     

Synthesis and Luminescence Property of 4,4＇-Bis（2,2-di（4-fluorophenyl）vinyl）biphenyl for Organic Blue-Light-Emitting Diodes

The novel fluorinated distyrylarylene, 4,4＇-bis（2,2-di（4-fluorophenyl）vinyl）biphenyl （DFPVBi）, was synthesized and fully characterized. The structure was confirmed with IR, 1↑H NMR, 13↑C NMR, 19↑F NMR and MS analyses. Its electronic and photoluminescence properties were investigated by UV-Vis absorption, cyclic voltammetry and fluorescence spectroscopy. The energy levels of the highest occupied molecular orbital （HOMO） and the lowest unoccupied molecular orbital （LUMO） are --5.77 and --2.75 eV, respectively. The electroluminescence proper- ties of the organic light-emitting diode fabricated by DFPVBi were also studied. The device exhibits a pure blue emission peaked at 454 nm, which indicates a maximum luminance of 5872 cd/m ^2 at 14.2 V and a maximum current efficiency of 2.82 cd/A at 10V, respectively.     

Optimizing Optoelectronic Properties of Pyrimidine‐Based TADF Emitters by Changing the Substituent for Organic Light‐Emitting Diodes with External Quantum Efficiency Close to 25 % and Slow Efficiency Roll‐Off

A series of green butterfly‐shaped thermally activated delayed fluorescence (TADF) emitters, namely PXZPM , PXZMePM , and PXZPhPM , are developed by integrating an electron‐donor (D) phenoxazine unit and electron‐acceptor (A) 2‐substituted pyrimidine moiety into one molecule via a phenyl‐bridge π linkage to form a D –π–A–π–D configuration. Changing the substituent at pyrimidine unit in these emitters can finely tune their emissive characteristics, thermal properties, and energy gaps between the singlet and triplet states while maintaining frontier molecular orbital levels, and thereby optimizing their optoelectronic properties. Employing these TADF emitters results in a green fluorescent organic light‐emitting diode (OLED) that exhibits a peak forward‐viewing external quantum efficiency (EQE) close to 25 % and a slow efficiency roll‐off characteristic at high luminance.     

Quantum‐chemical,IR, NMR,and X‐ray diffraction studies on 2‐(4‐chlorophenyl)‐1‐methyl‐ 1H‐benzo[d]imidazole

The title molecule, 2‐(4‐chlorophenyl)‐1‐methyl‐1H‐benzo[d]imidazole (C₁₄H₁₁ClN₂), was prepared and characterized by ¹H NMR, ¹³C NMR, IR, and single‐crystal X‐ray diffraction. The molecular geometry, vibrational frequencies, and gauge including atomic orbital (GIAO) ¹H and ¹³C NMR chemical shift values of the title compound in the ground state have been calculated by using the Hartree‐Fock (HF) and density functional theory (DFT/B3LYP) method with 6‐31G(d) basis sets, and compared with the experimental data. The calculated results show that the optimized geometries can well reproduce the crystal structural parameters, and the theoretical vibrational frequencies and GIAO ¹H and ¹³C NMR chemical shifts show good agreement with experimental values. The energetic behavior of the title compound in solvent media has been examined using B3LYP method with the 6‐31G(d) basis set by applying the Onsager and the polarizable continuum model (PCM). Besides, molecular electrostatic potential (MEP), frontier molecular orbitals (FMO) analysis, and nonlinear optical (NLO) properties of the title compound were investigated by theoretical calculations. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

A DFT/TDDFT study of porphyrazines and phthalocyanine oxo‐titanium derivatives as potential dyes in solar cells

Density functional theory and time dependent density functional theory calculations at the level of LDA/BP86/TZ2P were performed systematically on several Ti(IV) complexes of porphyrazines and one phthalocyanine. We performed an analysis of the frontier molecular orbitals of the ground state electronic structures and also discuss in particular the good concordance of our results with the experimental data, which affords to predict the geometrical and optical properties of new complexes ( 3 , 4 , and 7 ). We also emphasize the characterization of the UV–vis absorption spectra and propose transitions that contribute to the Q and B bands. Some useful calculated properties in complexes 2 , 3 , and 7 , like: high light absorption in the visible region of the spectra, transitions involved in these bands with a determined direction, charge separation, bigger highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO‐LUMO) gaps than complexes 4 and 5 , and the energy of their LUMO orbitals (that are higher than the lowest energy level of the conduction band of the TiO₂) indicate that system complexes 2 , 3 , and 7 could act as light‐harvesting sensitizers for dye‐sensitized solar cells (DSCs). These proposals were made using a model of the previously experimentally known phthalocyanine, which was used as sensitizer in DSCs devices, comparing its electronic properties with the herein proposed sensitizers. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Ab initio and semiempirical computational studies on 1‐{(2E)‐2‐[(aminocarbonothioyl)hydrazono]‐2‐(3‐mesityl‐3‐methylcyclobutyl)ethyl}‐pyrrolidine‐2,5‐dione

The molecular geometry, vibrational frequencies, and gauge including atomic orbital (GIAO) ¹H‐ and ¹³C NMR chemical shift values of the title compound in the ground state have been calculated using the Hartree‐Fock (HF) and density functional theory (DFT) methods with 6‐31G(d) basis sets, and compared with the experimental data. The calculated results show that the optimized geometries can well reproduce the crystal structural parameters and the theoretical vibrational frequencies, and ¹H‐ and ¹³C NMR chemical shift values show good agreement with experimental data. To determine conformational flexibility, the molecular energy profile of the title compound was obtained by semiempirical (AM1) calculations with respect to the selected torsion angle, which was varied from ?180° to +180° in steps of 10°. The energetic behavior of the title compound in solvent media was examined using the B3LYP method with the 6‐31G(d) basis set by applying the Onsager and the polarizable continuum model (PCM). The results obtained with these methods reveal that the PCM method provided more stable structure than Qnsager's method. By using TD‐DFT method, electronic absorption spectra of the title compound have been predicted and a good agreement with the TD‐DFT method and the experimental one is determined. The predicted nonlinear optical properties of the title compound are much greater than ones of urea. In addition, the molecular electrostatic potential (MEP), frontier molecular orbitals (FMO) analysis, NBO analysis and thermodynamic properties of the title compound were investigated using theoretical calculations. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

DFT study of the carbon‐ and nitrogen‐pivot lariat crown ethers and their complexes with alkali metal cations: Na+, K+

In this work, a quantum mechanical research of five lariat crown ethers(LCEs), 2‐methoxy‐15‐crown‐5( A ), N‐methoxy‐4‐aza‐15‐crown‐5( B ), N‐methoxy‐4‐aza‐18‐crown‐6( C ), N‐methoxyethyl‐4‐aza‐18‐crown‐6( D ), N,N′‐bis(2‐metho xyethyl)‐4,13‐diaza‐18‐crown‐6( E ), which are based on either 15‐crown‐5 or 18‐crown‐6 frameworks and contain various pendant arms extending from either carbon or nitrogen atoms on the crown frameworks, had been done using density functional theory with B3LYP/6‐31G* method to obtain the electronic and geometrical structures of the LCEs and their complexes with alkali metal ions: Na⁺ and K⁺. The nucleophilicity of LCEs had been investigated by the Fukui functions. For complexes, the match between the cation and cavity size, the status of interaction between alkali metal ions and donor atoms in the LCEs, and the sidearm effect of the LCEs had been analyzed through the other calculated parameters, such as, highest occupied molecular orbital energy, lowest unoccupied molecular orbital energy, and energy gaps. In addition, the enthalpies of complexation reaction had been studied by the calculated thermodynamic data (298 K). The calculated results are all in a good agreement with the experimental data for the complexes. © 2009 Wiley Periodicals, Inc. J Comput Chem 2009