Excited states and electronic spectra of annulated dinuclear free-base phthalocyanines: a theoretical study on near-infrared-absorbing dyes

The electronic excited states and electronic absorption spectra of annulated dinuclear free-base phthalocyanine (C(58)H(30)N(16)) are studied through quantum chemical calculations using the symmetry-adapted cluster-configuration interaction (SAC-CI) method. Three tautomers are possible with respect to the position of the pyrrole protons; therefore, the SAC-CI calculations for these tautomers were performed. The structures of the Q-band states are discussed based on the character of their molecular orbitals. The lower energy shift of the Q-bands because of dimerization is explained by the decrease in the HOMO-LUMO gaps resulting from the bonding and antibonding interactions between the monomer units. The electronic dipole moments of the nonsymmetric tautomer were calculated, and the possibility of charge-separated excited states is discussed. The relative energies of these tautomers are examined using density functional theory (DFT) calculations for several peripheral substituents. The relative energies of these tautomers significantly depend on the substituents, and therefore, the abundance ratios of the three tautomers were affected by the substituents. The absorption spectra were simulated from the SAC-CI results weighted by the Boltzmann factors obtained from the DFT calculations. The SAC-CI spectra reproduce the experimental findings well. The thermal-averaged SAC-CI spectra could explain the observed substituent effect on the structure of the Q-bands in terms of the relative stabilities and the abundance ratios of the tautomers. The SAC-CI and time-dependent density functional theory calculations are also compared. The CAM-B3LYP results agreed with the trends of the SAC-CI results; however, the CAM-B3LYP calculation overestimated the excitation energies in comparison with the SAC-CI and experimental results.     

Theoretical investigation of one- and two-photon absorption properties of platinum acetylide chromophores

In this paper, we have theoretically investigated bis((4-phenylethynyl)phenyl) ethynyl)bis(trimethylphosphine)platinum(II) (PE2) and its analogs three platinum acetylide complexes (1-3) that feature highly pi-conjugated ligands (alkynyl-dimethylfluorene substituted with electron-donating or -withdrawing moieties). The geometrical and electronic structures are calculated at the ECP60MWB//6-31G*(H, C, P, N, S) basis set level by the density functional theory (DFT) method; one-photon absorption properties have been calculated by using time-dependent DFT (TDDFT) and Zerner's intermediate neglect of differential overlap (ZINDO) methods, and two-photon absorption (TPA) properties are obtained with the ZINDO/sum-over-states method. The values of beta(sp) and beta(d) for Pt are adjusted to -1 eV and -28.5 eV, respectively, to make one-photon absorption spectra calculated by ZINDO closest to the experimental data and TDDFT results. The calculated results indicate that all molecules in this work (involving cis isomers of molecules 1-3) take on two TPA peaks in the 600-800 nm region. The peak at 700-750 nm should not be simply attributed to the appearance of noncentrosymmetric cis isomers in solution, although trans and cis isomers adhere to a different selection rule. Every TPA peak results from its transition character. Molecules 1-3 show greater two-photon absorption strength compared with PE2 and retain good transparency.     

1,3-二苯基-5-吡唑啉酮三种异构体的结构及其发光性能

本文以1,3-二苯基-5-吡唑啉酮(DPP)为研究对象,采用不同溶剂对其进行重结晶,得到了3种不同颜色和不同构型的异构体。通过XRD粉末衍射、IR、1H NMR等确定了3种异构体的组成和结构,通过荧光光谱研究了它们的发光行为。结果表明这类化合物具有聚集诱导发光性能和光异构化性能,而且溶剂对产物的构型及发光性能均有明显的影响。此外,将该化合物与无规聚苯乙烯复合制备的薄膜也具有很好的荧光性能,在防伪领域具有潜在的应用。     

Chemistry, photophysics, and ultrafast kinetics of two structurally related Schiff bases containing the naphthalene or quinoline ring

The two structurally related Schiff bases, 2-hydroxynaphthylidene-(8-aminoquinoline) (HNAQ) and 2-hydroxynaphthylidene-1(')-naphthylamine (HNAN), were studied by means of steady-state and time resolved optical spectroscopies as well as time-dependent density functional theory (TDDFT) calculations. The first one, HNAQ, is stable as a keto tautomer in the ground state and in the excited state in solutions, therefore it was used as a model of a keto tautomer of HNAN which exists mainly in its enol form in the ground state at room temperature. Excited state intramolecular proton transfer in the HNAN molecule leads to a very weak (quantum yield of the order of 10(-4)) strongly Stokes-shifted fluorescence. The characteristic time of the proton transfer (about 30 fs) was estimated from femtosecond transient absorption data supported by global analysis and deconvolution techniques. Approximately 35% of excited molecules create a photochromic form whose lifetime was beyond the time window of the experiment (2 ns). The remaining ones reach the relaxed S(1) state (of a lifetime of approximately 4 ps), whose emission is present in the decay associated difference spectra. Some evidence for the back proton transfer from the ground state of the keto form with the characteristic time of approximately 13 ps was also found. The energies and orbital characteristics of main electronic transitions in both molecules calculated by TDDFT method are also discussed.     

Investigation of the electronic spectra and excited-state geometries of poly(para-phenylene vinylene) (PPV) and poly(para-phenylene) (PP) by the symmetry-adapted cluster configuration interaction (SAC-CI) method

The symmetry-adapted cluster-configuration interaction (SAC-CI) method has been used to investigate the optical and geometric properties of the oligomers of poly(para-phenylene vinylene) (PPV) and poly(para-phenylene) (PP). Vertical singlet and triplet absorption spectra and emission spectra have been calculated accurately; the mean average deviation from available experimental results lies within 0.2 eV. The chain length dependence of the transition energies has been improved in comparison to earlier TDDFT and MRSDCI calculations. The present analysis suggests that conventional TDDFT with the B3LYP functional should be used carefully, as it can provide inaccurate estimates of the chain length dependence of the excitation energies of these molecules with long pi conjugation. The T1 state was predicted to be at a lower energy, by 1.0-1.5 eV for PPV and by 0.9-1.7 eV for PP, than the S1 state, which indicates a localized T1 state with large exchange energy. By calculating the SAC-CI electron density difference between the ground and excited states, the geometry relaxations due to excitations can be analyzed in detail using electrostatic force theory. For trans-stilbene, the doubly excited 21Ag state was studied, and the calculated transition energy of 4.99 eV agrees very well with the experimental value of 4.84 eV. In contrast to previous ab initio calculations, we predict this doubly excited 21Ag state to lie above the 11Bu state.     

Low-lying excited states of C120 and C151: a multireference perturbation theory study

Excited states of two 7-aminocoumarin derivatives, coumarin 120 (7-amino-4-methylcoumarin) and coumarin 151 (7-amino-4-trifluoromethylcoumarin), were investigated using generalized multiconfigurational quasidegenerate perturbation theory (GMC-QDPT), multiconfigurational quasidegenerate perturbation theory (MC-QDPT) and time-dependent density functional theory (TDDFT) with the B3LYP and CAM-B3LYP functionals. The absorption and fluorescence spectra of C120 and C151 were calculated. We elucidated the characters of the low-lying states of C120 and C151. The absorption spectra calculated with GMC-QDPT and TDDFT B3LYP agreed well with the experimental data, while for the fluorescence spectra, the TDDFT calculations overestimated the fluorescence spectra compared to GMC-QDPT calculations. Utilizing active spaces with large numbers of electrons and orbitals for reference functions, GMC-QDPT showed a better performance than MC-QDPT with a complete active space self-consistent field (CASSCF) reference of active space with smaller number of electrons and orbitals. In our gas phase calculation, we found that the optimized structures for the first excited states have a planar amino group with a CN single bond, while the amino group is pyramidal in the ground state.     

3-(3’-吡啶基)-6-芳基-1,2,4-三唑并[3,4-b]-1,3,4-噻二唑衍生物基态和激发态性质

用密度泛函B3LYP方法对3-(3’-吡啶基)-6-芳基-1,2,4-三唑并[3,4-b]-1,3,4-噻二唑衍生物(芳基为苯基、3-吡啶基和苯乙烯基)进行基态几何构型全优化, 计算分子的电离势IP和电子亲和势EA等相关能量, 并用Zerner间略微分重叠(ZINDO)和含时密度泛函(TDDFT)方法计算吸收光谱, 用单组态相互作用方法(CIS)优化三种化合物分子的S1激发态结构, 分析其能量与发射光谱的关系, 计算溶剂中分子的吸收和发射光谱, 并与实验结果对照. 计算结果表明, 从3-(3’-吡啶基)-6-苯基-1,2,4-三唑并[3,4-b]-1,3,4-噻二唑分子(化合物A)到3-(3’-吡啶基)-6-(3’-吡啶基)-1,2,4-三唑并[3,4-b]-1,3,4-噻二唑分子(化合物B)以及3-(3’-吡啶基)-6-对乙烯苯基-1,2,4-三唑并[3,4-b]-1,3,4-噻二唑分子(化合物C)的电子亲和势依次增大, 愈来愈容易接受电子, 吸收光谱和发射光谱红移.     

Experimental and theoretical study of three new benzothiazole-fused carbazole derivatives

Three new D-π-A type compounds, each containing one benzothiazole ring as an electron acceptor and one N-ethylcarbazole group as electron donor, were synthesized and characterized by elemental analysis, NMR, MS and thermogravimetric analysis. The absorption and emission spectra of three compounds were experimentally determined in several solvents and were simultaneously computed using density functional theory (DFT) and time-dependent density functional theory (TDDFT). The calculated reorganization energy for hole and electron indicates that three compounds are in favor of hole transport than electron transport. The calculated absorption and emission wavelengths are well coincident with the measured data. The calculated lowest-lying absorption spectra can be mainly attributed to intramolecular charge transfer (ICT). And the calculated fluorescence spectra can be mainly described as originating from an excited state with intramolecular charge transfer (ICT) character. The results show that three compounds exhibited excellent thermal stability and high fluorescence quantum yields, indicating their potential applications as excellent optoelectronic material in optical field.     

Experimental and quantum chemical investigation of photochemical properties of a covalently bound bis(styrylquinoline) dyad

1,3-Bis(4-(2-quinoline-2-vynyl)phenoxy)propane a bis(styrylquinoline) dyad (S3S), has been synthesized and investigated. A comparison of S3S with the model 2-(4-methoxystyryl)quinoline (MeOSQ) has shown that integration of two styrylquinoline fragments (SQ) into the covalently bound dyad affects neither spectral properties nor the initial rate of the transcis photoisomerization reaction, but it results in both a change of the photolysis kinetics in general and the enrichment of the photostationary state in the isomer that has had a higher molar absorption coefficient at the irradiation wavelength. The kinetic scheme of the dyad photolysis including four isomers and eight reactions has been analyzed. The photoisomerization quantum yield of the SQ moiety of the dyad is half that of MeOSQ. Density functional theory (DFT) B3LYP/6–31G* calculation has revealed that the styrylquinoline nuclei in both MeOSQ and the S3S dyad have close geometrical parameters and electron structure. Absorption spectra have been calculated by the TDDFT method in the isolated-molecule approximation for an intermolecular hydrogen bonding-stabilized cluster with the ethanol molecule and in terms of the polarized continuum model (PCM). The absorption spectrum of the trans (E)-isomer is represented as spectra of two s-conformers, and the TDDFT method for the cis (Z)-isomer underestimates the energy of the long-wavelength absorption band.     

Hydrogen Bonding Effects on the Photophysical Properties of 2,3-dihydro-3-keto-1H-pyrido[3,2,1-kl]phenothiazine

Time-dependent density functional theory (TDDFT) and femtosecond transient absorption spectroscopy were used to investigate the photophysical properties of 2,3-dihydro-3-keto-1H-pyrido[3,2,1-kl]phenothiazine (PTZ4) and 3-keto-1H-pyrido[3,2,1-kl]phenothiazine (PTZ5). The calculated results obtained from TDDFT suggest that the red-shifts of the absorption spectra of these two fluorophores in methanol are due to the formation of hydrogen-bonded complexes at the ground state. Four conformers of PTZ4 were obtained by TDDFT. The two fluorescence peaks of PTZ4 in tetrahydrofuran (THF) came from the ICT states of the four conformers. The fluorescence of PTZ4 in THF showed a dependence on the excitation wavelength because of butterfly bending. The excited state dynamics of PTZ4 in THF and methanol were obtained by transient absorption spectroscopy. The lifetime of the excited PTZ4 in methanol was 53.8 ps, and its relaxation from the LE state to the ICT state was completed within several picoseconds. The short lifetime of excited PTZ4 in methanol was due to the formation of out-of-plane model hydrogen bonds between PTZ4 and methanol at the excited state.     

Optical and photophysical properties of indolocarbazole derivatives

We present a study of the optical and photophysical properties of five ladder indolo[3,2-b]carbazoles, namely, M1, M2, M3, M4, and M5. The ground-state optimized structures were obtained by B3LYP/6-31G* density functional theory (DFT) calculations, whereas the optimization (relaxation) of the first singlet excited electronic state (S1) was performed using the restricted configuration interaction (singles) (RCIS/6-31G*) approach. The excitation to the S1 state does not cause important changes in the geometrical parameters of the compounds, as corroborated by the small Stokes shifts. The excitation and emission energies have been obtained by employing the time-dependent density functional theory (TDDFT). For all the compounds, excitation to the S1 state is weakly allowed, whereas the S2 <-- S0 electronic transition of each oligomer possesses a much larger oscillator strength. The absorption and fluorescence spectra of the compounds have been recorded in chloroform. A reasonable agreement is obtained between TDDFT vertical transition energies and the (0,0) absorption and fluorescence bands. On one hand, the pattern of the aliphatic side chains does not affect the absorption and fluorescence maxima of the compounds. On the other hand, the replacement of aliphatic chains by phenyl or thiophene rings induces hypsochromic shifts in the absorption and fluorescence spectra. Finally, the fluorescence quantum yield and lifetime of the compounds in chloroform have been obtained. From these data, the radiative and nonradiative rate constants of the deactivation of the S1 state have been determined.     

Ground-state, excited-singlet-state, and excited-triplet-state energy levels and photophysics of the three rotational isomers of isophthalaldehyde vapor

Emission, excitation, and absorption spectra of isophthalaldehyde (benzene-1,3-dicarboxaldehyde) vapor have been measured at different temperatures, along with the UV-vis and IR absorption spectra in solution. Analyses of the temperature dependence of the phosphorescence and excitation spectra of isophthalaldehyde vapor revealed the energetic relationships among the three rotational isomers in the T1(n, pi*), S1(n, pi*), and ground states. This appears to be the first example of the system where the S0, T1, and S1 energy levels are determined for the three rotational isomers. The phosphorescence, fluorescence, and excitation origins of the three rotamers were assigned on the basis of the results of the density functional theory (DFT) and semiempirical SCF-MO calculations and infrared data as well as on the basis of the temperature dependence of the emission and excitation spectra.     

Quantum-chemical investigation of the mechanism of trans-cis photoisomerization of 4-[2-(2-chlorophenyl)vinyl]-6,6-dimethyl-2-oxo-1,2,5,6-tetrahydropyridine-3-carbonitrile

A quantum-chemical investigation has been carried out by the semiempirical AM1 method of the trans-cis photoisomerization mechanism of 4-[2-(2-chlorophenyl)vinyl]-6,6-dimethyl-2-oxo-1,2,5,6-tetra- hydropyridine-3-carbonitrile. It was shown that the isomerization process proceeds in the excited singlet state S₁ by rotation of the 2-chlorophenyl substituent around the C(2)–C(3) bond. Electronic absorption spectra of the isomers were calculated by the INDO/S method Transitions caused by exitation of an electron from HOMO to LUMO were characterized by the greatest intensity.     

Predictions of the electronic absorption and emission spectra of luciferin and oxyluciferins including solvation effects

The ground and excited state properties of luciferin (LH(2)) and oxyluciferin (OxyLH(2)), the bioluminescent chemical in the firefly, have been characterized using the configuration interaction singles (CIS) and time dependent density functional (TDDFT) methods. The effects of solvation on the electronic absorption and emission spectra of luciferin and oxyluciferin are predicted with a self-consistent isodensity polarized continuum model of the solvent using both the configuration interaction singles model and time dependent density functional theory. The S(0)-->S(1) vertical excitation energies in the gas phase and in water are obtained with both methods. Optimizations of the excited state geometries permit the first predictions of the fluorescence spectra for these biologically important molecules. Shifts in both the absorption and emission spectra on proceeding from the gas phase to aqueous solution also are predicted.     

Experimental and theoretical study of 10-methoxy-2-phenylbenzo[h]quinoline

10-Methoxy-2-phenylbenzo[h]quinoline (MPBQ) has been synthesized and characterized by NMR and X-ray single crystal diffraction. Both the ground and the lowest singlet excited-state geometries of MPBQ were optimized by B3LYP and ab initio CIS methods at 6-31G (d,p) level, respectively. The absorption and emission spectra of the compound were experimentally determined in CH(3)CN solution and were simultaneously computed using density functional theory (DFT) and time-dependent density functional theory (TDDFT) in CH(3)CN solution. The calculated absorption and emission wavelengths were in good agreement with the experimental ones. The calculated lowest-lying absorption spectra can be mainly attributed to intramolecular charge transfer (ICT). And the calculated fluorescence spectra can be mainly described as originating from an excited state with intramolecular charge transfer (ICT) character. These results show that MPBQ exhibited excellent thermal stability and could serve as a useful photoluminescence material.     

Investigation of the structure, the optical properties, and the photophysics of some indolocarbazoles having terminal aromatic rings

Structures, optical properties, and photophysics of ladder indolo[3,2-b]carbazoles substituted symmetrically by phenylene and thiophene rings have been investigated theoretically and experimentally. The ground state optimized structures were obtained using the density functional theory (DFT) as approximated by the B3LYP functional and employing the 6-31G^* basis set. All derivatives were found nonplanar in their electronic ground states. The character and the energy of the singlet–singlet electronic transitions have been investigated by applying the time-dependent density functional theory (TDDFT) to the correspondingly optimized-ground-state geometries. The ab initio restricted configuration interaction (singles) method (RCIS/6-31G^*) was adopted to obtain the first singlet excited-state structures (S₁) of the molecule. TDDFT calculations performed on the S₁ optimized geometries was used to obtain emission energies. UV–vis and fluorescence spectroscopies were analyzed in conjunction with theoretical calculations. The computed excitation and emission energies were found in reasonable agreement with the experimental absorption and fluorescence spectra. Finally, the photophysical behavior of the indolocarbazoles have been studied by means of steady state and time resolved fluorescence. The overall data have allowed the determination of the rate constants for the radiative and nonradiative decay processes. Both theoretical and experimental data show that the replacement of phenylene rings by thiophene units induces a red shift in the absorption and fluorescence spectra. This behavior is interpreted in terms of the electron donor properties of the thiophene ring. On the other hand, the change of the substitutional pattern, from 2,8 to 3,9, causes a significant hypsochromic shift of the absorption and fluorescence bands.     

3-(3′-吡啶基)-6-芳基-1，2，4-三唑并[3，4-b]-1，3，4-噻二唑衍生物基态和激发态性质

用密度泛函B3LYP方法对3-(3'-吡啶基)-6-芳基-1,2,4-三唑并[3,4-b]-1,3,4-噻二唑衍生物(芳基为苯基、3-吡啶基和苯乙烯基)进行基态几何构型全优化,计算分子的电离势I_p和电子亲和势E_A等相关能量,并用Zerner间略微分重叠(ZINDO)和含时密度泛函(TDDFT)方法计算吸收光谱,用单组态相互作用方法(CIS)优化三种化合物分子的S_1激发态结构,分析其能量与发射光谱的关系,计算溶剂中分子的吸收和发射光谱,并与实验结果对照.计算结果表明,从3-(3'-吡啶基)-6-苯基-1,2,4-三唑并[3,4-b]-1,3,4-噻二唑分子(化合物A)到3-(3'-吡啶基)-6-(3'-吡啶基)-1,2,4-三唑并[3,4-b]-1,3,4-噻二唑分子(化合物B)以及3-(3'-吡啶基)-6-对乙烯苯基-1,2,4-三唑并[3,4-b]- 1,3,4-噻二唑分子(化合物C)的电子亲和势依次增大,愈来愈容易接受电子,吸收光谱和发射光谱红移.     

C62及其吡啶衍生物结构与电子光谱的密度泛函理论研究

采用密度泛函理论(DFT)方法, 在TZP基组水平下计算C62及其吡啶衍生物几何与电子结构, 在全优化构型基础上, 采用TD-DFT方法对其低激发态进行计算, 预测其电子吸收光谱. 结果表明, 四种异构体的电子光谱中, 特征吸收来自C62内部的跃迁贡献, 也包括取代基到C62的电子转移. 取代基中N原子位置对490 nm左右吸收带的强度有影响, 两种顺式结构表现较为明显, 而两种反式结构衍生物光谱特征基本相同.     

7-氮杂吲哚衍生物分子基态和激发态性质的理论研究

用从头算HF和密度泛函B3LYP方法对7-氮杂吲哚衍生物1,3-二(N-7-氮杂吲哚基)苯、1,3,5 三(N-7-氮杂吲哚基)苯和4,4′-二(N-7-氮杂吲哚基)联苯进行全优化, 计算分子的电离势IP和电子亲和势EA等相关能量, 并用ZINDO和TDDFT方法计算吸收光谱, 用CIS优化三种化合物分子的S1激发态结构, 并分析其能量与发射光谱的关系, 计算溶剂中分子的吸收和发射光谱, 并与实验结果对照. 计算结果表明, 从7-氮杂吲哚到上述三种衍生物依次愈来愈容易接受空穴, 吸收和发射光谱红移.     

Theoretical study of vibrational and optical spectra of methylene-bridged oligofluorenes

We report a systematic characterization of methylene-bridged fluorene oligomers constructed of two, four, six, and eight aromatic rings using time-dependent density functional theory (TDDFT), the ab initio approximate coupled-cluster singles and doubles (CC2) method, and semiempirical spectroscopic Zerner's intermediate neglect of differential overlap method (ZINDO/S). Geometry optimizations have been performed for the ground state and for the first electronically excited state. Vertical excitations and the fluorescence transition from the lowest excited state have been calculated. Computed ground-state geometries and infrared spectra for fluorene are in good agreement with experimental results. The RI-CC2 and ZINDO/S absorption and fluorescence spectra agree very well with the available experimental data for studied fluorene oligomers and for para oligophenylenes films. On the other hand, TDDFT calculations underestimate excitation and fluorescence energies systematically for larger systems (N > 4) in comparison with the above-mentioned results. The effective conjugation length was estimated to 13-14 repeat units. The computed radiative lifetimes for the fluorene molecule show good agreement with experiment within realistic expectations. The decrease of the radiatiave fluorescence lifetime with the increase in the conjugation length has been discussed also.