A theoretical investigation into the photophysical properties of ruthenium polypyridine-type complexes

Excited states of ruthenium polypyridine-type complexes have always attracted the interest of chemists. We have recently found evidence of a remarkable long-lived excited state (30 micros) for a Ru(II) complex containing a heteroditopic ligand that can be viewed as a fused phenanthroline and salophen ligand.1 To unravel this intriguing electronic property, we have used density functional theory (DFT) calculations to understand the ground-state properties of [(bpy)(2)Ru(LH(2))](2+), where LH(2) represents N,N'-bis(salicylidene)-(1,10-phenanthroline)diamine. Excited singlet and triplet states have been examined by the time-dependent DFT (TDDFT) formalism and the theoretical findings have been compared with those for the parent complex [Ru(bpy)(3)](2+). The outstanding result is the presence of excited states lower in energy than the metal-to-ligand charge-transfer states, originating from intraligand charge transfer (ILCT) from the phenolic rings to the phenanthroline part of the coordinated LH(2). The spin density distribution for the lowest triplet state provides evidence that it is in fact the lowest triplet state of the free ligand. Correlation between the energy level diagram of orbitals for the ground state and that for the (3)ILCT state clearly establishes that the ruthenium retains its formal Ru(II) oxidation state. The quenching of the luminescence and the evidence of the long-lived excited state observed for [(bpy)(2)Ru(LH(2))](2+) are discussed in the light of the computational results.     

Meta-substituted Ru rigid rods for sensitization of TiO2

Ruthenium polypyridyl rigid-rod compounds with phenylene–ethynelene (OPE) spacers and an isophthalic acid (Ipa) binding group were synthesized and characterized for sensitization of nanocrystalline TiO₂ (anatase) thin films. Density functional theory predicted that the most stable structure oriented the isophthalic group about 45° from normal to the TiO₂ surface. Comparative experimental studies of meta- and para-isomers revealed small changes in the ground state absorption spectra and very similar excited state and redox properties. The excited state injection yields (inj = 0.15 ± 0.03) into nanocrystalline TiO₂ and the subsequent charge recombination rates were found to be insensitive to the isomer utilized. Meta-substitution enabled the synthesis of sensitizers with two Ru^II sensitizers that displayed enhanced sunlight absorption relative to the monomeric compound.     

Theoretical studies on the electronic structures and spectroscopic properties of a series of novel N?C?N‐coordinating Pt(II) complexes

The electronic structures and spectroscopic properties of the three tridentate cyclometalated Platinum(II) complexes PtL¹Cl [L¹ = 1,3‐di(2‐pyridyl)‐5‐methyl‐benzene] ( 1 ), PtL²Cl [L² = 1‐(2‐pyridyl)‐3‐(1‐pyrazolyl)‐5‐methyl‐benzene] ( 2 ), and PtL³Cl [L³ = 1,3‐bis(1‐pyrazolyl)‐5‐methyl‐benzene] ( 3 ) were calculated to explore their spectroscopic nature. The geometry structures of 1 – 3 in the ground and excited states were optimized under the density functional theory (DFT) and the single‐excitation configuration interaction (CIS) level, respectively. The absorption and emission spectra in CH₂Cl₂ solution were calculated by the time‐dependent density‐functional theory (TD‐DFT) with the polarized continuum model solvent model. As revealed from the calculations, the LUMO of 1 and 2 are localized on phenyl and pyridyl, but that of 3 has 50.3% π*(pyrazolyl) and 47.8% π*(phenyl). The energy gap of the d‐d state was much greater than that of the CT transitions. With the replacement of pyridyl by pyrazolyl, the electron‐donating ability of N atom decreases, whereas the LUMO energy level increases. The lowest‐energy absorptions and emissions are blue‐shifted in the order 1 > 2 > 3 , which are assigned as the ILCT/MLCT/LLCT and ³ILCT/³MLCT/³LLCT characters, respectively. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Verbenone-based push–pull chromophores with giant first hyperpolarizabilities: A new structure–property correlation study

Novel chromophores Ch1–8 based verbenone bridge with various strong donors and acceptors were designed for applications in nonlinear optics, and the nonlinear optical (NLO) properties of those verbenone-type chromophores were systematically investigated using the bond length alteration (BLA) theory, two states model (TSM) and sum-over-states (SOS) model. The results show that several verbenone-based chromophores possess remarkably large molecular second-order hyperpolarizabilities, which is due to its electron distribution close to the cyanine limit, the appropriate strength of acceptor, rather large change in dipole moment and low excitation energy. Computed hyperpolarizability (β_tot) of Ch6 also approach an outstanding 2922 × 10⁻³⁰ esu in TFE. The hyperpolarizability density analyses and two states model (TSM) were carried out to make a further insight into the origination of molecular nonlinearity of this unique system, suggesting that tuning structure of acceptor and polarity of the medium have great influence on the second-order nonlinear optical properties. More importantly, chromophores Ch1–Ch8 exhibited distinct features in two-dimensional second order NLO responses, and the strong electro-optical Pockels effect and optical rectification responses. The excellent electronic sum frequency generations (SFG) and difference frequency generations (DFG) effect are observed in these verbenone-type chromophores. These chromophores have a possibility to be appealing second-order nonlinear optical (NLO) materials, data storage materials and DSSCs materials from the standpoint of large β values, high LHE, and excellent two-dimensional second order NLO responses.     

Potential functions of inversion of R2CO (R=H, F, Cl) molecules in the lowest excited electronic states

The inversion potentials of R₂CO (R=H, F, Cl) molecules in the lowest excited electronic states were determined from experimental data using various model potential functions and approximations for the kinetic energy operator of inversion motion. The estimates of the heights of the barriers to inversion and the equilibrium values of the inversion coordinate for the H₂CO molecule in the S₁ and T₁ states are fairly stable. The results for the F₂CO and Cl₂CO molecules are strongly dependent on the approximation used; for these molecules, the most reliable parameters of the potential functions were chosen. The problem of qualitative characteristics of the shape of inversion potentials is discussed using the results ofab initio quantum-chemical calculations of the molecules under study. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 645–651, April, 1999.     

Synthesis of substituted poly(1-vinylpyrene)s and investigation of their fluorescent properties

A series of functionalized linear poly(1-vinylpyrene) (PVP) polymers bearing substituents such as ? NO₂, ? CHO, ? NH₂, ? Br, and ? CH?C(CN)₂, were prepared by chemical modification of PVP in solution. The degree of substitution in PVP? CH?C(CN)₂ was varied from 40% to nearly 100% by control of the reaction conditions. The other polymers were partially functionalized. The UV-visible and fluorescence spectroscopy of the polymers were studied in solution. The influence of solvent polarity, excitation energy, and degree of substitution on the fluorescence of the polymers were examined. © 1993 John Wiley & Sons, In     

Molecular electric properties in electronic excited states: multipole moments and polarizabilities of H2O in the lowest1 B 1 and3 B 1 excited states

Summary The dipole and quadrupole moments and the dipole polarizability tensor components are calculated for the¹ B ₁ and³ B ₁ excited states of the water molecule by using the complete active space (CAS) SCF method and an extended basis set of atomic natural orbitals. The dipole moment in the lowest¹ B ₁ (0.640 a.u.) and³ B ₁ (0.416 a.u.) states is found to be antiparallel to that in the ground electronic state of H₂O. The shape of the quadrupole moment ellipsoid is significantly modified by the electronic excitation to both states investigated in this paper. All components of the excited state dipole polarizability tensor increase by about an order of magnitude compared to their values in the ground electronic state. The present results are used to discuss some aspects of intermolecular interactions involving molecules in their excited electronic states.     

Time-dependent Hartree-Fock calculations for the excited ‘S’ states of lithium isoelectronic sequence

Time-dependent HF (RPA) calculations have been performed to estimate the transition energies and excited state wavefunctions of Li, Be⁺, B²⁺ and C³⁺ for the transitions 1s ²2s ² S 1s ² ns ² S (n = 3,4, ... 8). The excitation energies and excited state wavefunctions are extracted from the position of the poles of a linearised variational functional. The excitation energies are in excellent agreement with those obtained spectroscopically. The excited state wavefunctions are utilised to find the matrix elements of different operators and the cusp values.     

Structures and Spectroscopic Properties of NaAs4 and Its Anions and Cations

The equilibrium geometries, vibrational frequencies, atomization energies, adiabatic electron separations, adiabatic detachment energies （ADE）, and adiabatic ionization potentials of the low-lying electronic states for the NaAs4 clusters and its ions were investigated employing the DFT method, and then compared with the photoelectron spectra. According to the computed results, reasonable assignments for the photoelectron spectra of NaAs4^- were suggested.     

Exohedral functionalization of fullerenes and supramolecular chemistry

We have investigated the exohedral functionalization of [60]fullerene, especially bisaddition; we have revealed the regioselectivity of bisaddition and the properties of obtained bisadducts. The bisaddition without any restriction generally shows low regioselectivity. The electronic and photophysical properties of bisadducts mainly depend on the addition patterns and are almost independent of the nature of addends. We have also attained the regioselective synthesis of bisadducts by controlling the distance and orientation between two reactive species with suitable covalent templates and their application into some functional materials. The synthesis of fullerene‐containing interlocked molecules, such as catenanes and rotaxanes, was accomplished by using a noncovalent interaction, mainly a donor‐acceptor interaction, in addition to the covalent functionalization. The bistable rotaxanes, which can serve as a molecular shuttle or switch, were also successfully prepared. DOI 10.1002/tcr.201000036     

Structure of electronically excited complexes in styrene and α-methylstyrene anion polymerizations

The spatial and electronic structure of styrene and α-methylstyrene monomer molecules and their complexes with living polymers in the ground singlet state (S ₀) and excited singlet (S ₁) and triplet (T ₁) states has been studied by RHF, ROHF/6-31G*, and DH quantum-chemical methods. The mechanism of anionic polymerization is considered in the context of the concept of electronic excitation in an elementary process. The excited states of (S·T)₁ biradical type are characterized by low energies (6–15 kcal/mole), which have the sense of activation energies E _a of chain propagation. Calculation gave higher values of E _a for free C^? anions compared to those for C^?M⁺ ion pairs, which indicates that anions show lower chemical activity in the general polymerization process.     

密度泛函理论处理激发态与多重态结构研究进展

用密度泛函理论处理分子激发态和电子多重态结构是密度泛函理论发展的重要方面, 研究工作一直很活跃。本文对近年来在这一领域取得的重要进展作简要的综述。     

Comparison of the capacity of nitrogen, oxygen, sulfur, and selenium atoms to exist in onium states. quantum-chemical investigation of isomeric model systems with two heteroatoms

HF, B3LYP, and MP2 calculations with the 6-31+G(d) basis set with correction to the energy of zero-point vibrations were carried out to determine the energy characteristics of model molecules containing two heteroatoms in the sp ³- and sp ²-hybrid states; different combinations of N, O, S, and Se atoms were studied. The stability of the onium states of the nitrogen atom was found to be greater than for its chalcogen analogs and the relative stability of onium states of the chalcogen analogs was found to depend on the hybridization of these atoms. Analysis of these results permitted us to construct a stability series of onium derivatives and to interpret the positional selectivity in electrophilic substitution reactions of five-membered heterocyclic compounds with one heteroatom. To J. Stradins, an outstanding and tireless scientist, with our deep respect and sincere affection. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1801–1808, December, 2008.     

Photophysical Properties of Benzoylgermane and para‐Substituted Derivatives: Substituent Effects on Electronic Transitions

In the present study, a selection of basic substitution patterns on benzoyl(trimethyl)germane was investigated using time‐dependent density‐functional theory (TDDFT) to explore the influence on the stability and on the relative order of the lowest excited electronic states. The theoretical results are in agreement with absorption and fluorescence measurements. We show that electron‐withdrawing groups decrease the energetic level of the lowest singlet and triplet state relative to the electron‐pushing systems resulting in red‐shifted radiative transitions (fluorescence). In the first triplet state electron‐withdrawing groups lead to an increased dissociation barrier and a close approach with the singlet ground state before the transition state in the triplet state is reached, favoring radiationless ground‐state recovery. The results are also in good agreement with empirical concepts of organic chemistry, therefore providing simple rules for synthetic strategies towards tuning the excited‐state properties of benzoylgermanes.     

三原子分子振转激发态的理论研究

三原子分子振转激发态的理论研究谢代前,鄢国森,田安民（四川大学化学系,成都,６１００６４）关键词振转激发态,三原子分子,变分法能级较高的振转激发态通常包含大振幅运动,其波函数分布于很广的势能面区域内,传统的正则模理论已不适合于解决这类问题．近年来,Ｈ...