The electronic absorption spectrum and excited state dipole moment of 3-fluoropyridine

The electronic absorption spectrum of 3-fluoropyridine in the vapour state and in solutions in different solvents in the region 3000-1900 Å has been measured and analysed. Three systems of absorption bands; n→π* transition I, π→π* transition II and π→π* transition III are identified. The oscillator strength of the absorption band systems due to the π→π* transition II and π→π* transition III and the excited state dipole moments associated with these transitions have been determined by the solvent-shift method.     

Synthesis,Electrochemistry, and Photophysical Studies of Ruthenium(II) Polypyridine Complexes with D–π–A–π–D Type Ligands and Their Application Studies as Organic Memories

A new class of ruthenium(II) polypyridine complexes with a series of D–π–A–π–D type (D=donor, A=acceptor) ligands was synthesized and characterized by ¹H NMR spectroscopy, mass spectrometry, and elemental analysis. The photophysical and electrochemical properties of the complexes were also investigated. The newly synthesized ruthenium(II) polypyridine complexes were found to exhibit two intense absorption bands at both high‐energy (λ=333–369 nm) and low‐energy (λ=520–535 nm) regions. They are assigned as intraligand (IL) π→π* transitions of the bipyridine (bpy) and π‐conjugated bpy ligands, and IL charge‐transfer (CT) transitions from the donor to the acceptor moiety with mixing of dπ(Ru^II)→π*(bpy) and dπ(Ru^II)→π*(L) MLCT characters, respectively. In addition, all complexes were demonstrated to exhibit intense red emissions at approximately λ=727–744 nm in degassed dichloromethane at 298 K or in n‐butyronitrile glass at 77 K. Nanosecond transient absorption (TA) spectroscopy has also been carried out, establishing the presence of the charge‐separated state. In order to understand the electrochemical properties of the complexes, cyclic voltammetry has also been performed. Two quasi‐reversible oxidation couples and three quasi‐reversible reduction couples were observed. One of the ruthenium(II) complexes has been utilized in the fabrication of memory devices, in which an ON/OFF current ratio of over 10⁴ was obtained.     

trans–cis Photoisomerization of Azobenzene‐Conjugated Dithiolato‐Bipyridine Platinum(II) Complexes: Extension of Photoresponse to Longer Wavelengths and Photocontrollable Tristability

Azobenzene derivatives modified with dithiolato‐bipyridine platinum(II) complexes were synthesized, revealing their highly extended photoresponses to the long wavelength region as well as unique photocontrollable tristability. The absorptions of trans‐ 1 and trans‐ 2 with one azobenzene group on the dithiolene and bipyridine ligands, respectively, cover the range from 300 to 700 nm. These absorptions are ascribed, by means of time‐dependent (TD)DFT calculations, to transitions from dithiolene(π) to bipyridine(π*), namely, interligand charge transfer (CT), π–π*, and n–π* transitions of the azobenzene unit, and π–π* transitions of the bipyridine ligand. In addition, only trans‐ 1 shows distinctive electronic bands, assignable to transitions from the dithiolene(π) to azobenzene(π*), defined as intraligand CT. Complex 1 shows photoisomerization behavior opposite to that of azobenzene: trans‐to‐cis and cis‐to‐trans conversions proceed with 405 and 312 nm irradiation, which correspond to excitation with the intraligand CT, and π–π* bands of the azobenzene and bipyridine units, respectively. In contrast, complex 2 shows photoisomerization similar to that of azobenzene: trans‐to‐cis and cis‐to‐trans transformations occur with 365 and 405 nm irradiation, respectively. Irradiation at 578 nm, corresponding to excitation of the interligand CT transitions, results in cis‐to‐trans conversion of both 1 and 2 , which is the longest wavelength ever reported to effect the photoisomerization of the azobenzene group. The absorption and photochromism of 4 , which has azobenzene groups on both the dithiolato and bipyridine ligands, have characteristics quite similar to those of 1 and 2 , which furnishes 4 with photocontrollable tristability in a single molecule using light at 365, 405, and 578 nm. We also clarified that 1 and 2 have high photoisomerization efficiencies, and good thermal stability of the cis forms. Complexes 3 and 5 have almost the identical photoresponse to those of their positional isomers, complexes 2 and 4 .     

Crystal structure, electronic properties and cytotoxic activity of palladium chloride complexes with monosubstituted pyridines

Palladium(II) complexes attract great attention due to their remarkable catalytic and biological activity. In the present study X-ray characterization, UV-Vis and Time-Dependent Density Functional Theory (TD-DFT) calculations for six PdCl(2)(XPy)(2) complexes (where: Py = pyridine; X = H, CH(3) or Cl) were applied in order to investigate substituent effects on their crystal structures and electronic properties and to combine the results with their catalytic and cytotoxic activity. The structures of complexes PdCl(2)(3-MePy)(2), PdCl(2)(4-MePy)(2) and PdCl(2)(2-ClPy)(2), have been described for the first time and we compared our results with available data for the whole series of six complexes. All compounds exhibit a square planar coordination geometry in which the palladium ion coordinates two nitrogen atoms of pyridine ligands and two chlorine atoms in trans positions. For complexes with ortho substituted XPy ligands a cis disposition of substituents takes place, whereas for other ligands: 3-MePy and 3-ClPy--the substituents are in trans positions. For XPy the energies of π-π* and n-π* transitions depend on the position and nature of the X substituent in the XPy ring. After complex formation a hipsochromic shift (24-34 nm) of π-π* and a bathochromic shift of n-π* bands are observed. The UV-Vis spectra of PdCl(2)(XPy)(2) confirm that square planar coordination geometry of complexes I-VI and two dπ-π* transitions are expected. With the help of the TD-DFT calculations we proved that dπ-π* transitions in solutions of PdCl(2)(XPy)(2) complexes result from MLCT (metal-to-ligand charge transfer) with contribution from chlorine atoms to palladium. We also studied substituent effects on cytotoxic properties of Pd(II) complexes against the human breast cancer cell line MCF7, the human prostate cancer cell line PC3, and the human T-cell lymphoblast-like cell line CCRF. The studied complexes were the most active against the CCRF cell line and less or even no cytotoxic effect was observed for PC3 cells. Complexes with MePy ligands showed increased cytotoxic activity compared to unsubstituted pyridine ligands.     

Nonlinear Absorbing Platinum(II) Diimine Complexes: Synthesis, Photophysics, and Reverse Saturable Absorption

A series of platinum(II) diimine complexes with different substituents on fluorenyl acetylide ligands (1?a-1?e) were synthesized and characterized. The influence of the auxiliary substituent on the photophysics of these complexes has been systematically investigated spectroscopically and theoretically (using density functional theory (DFT) methods). All complexes exhibit ligand-centered (1) π,π* transitions in the UV and blue spectral region, and broad, structureless (1) MLCT/(1) LLCT (1?a, 1?b, 1?d and 1?e) or (1) MLCT/(1) LLCT/(1) π,π* (1?c) absorption bands in the visible region. All complexes are emissive in solution at room temperature, with the emitting state is tentatively assigned to mixed (3) MLCT/(3) π,π* states. The degree of (3) π,π* and (3) MLCT mixing varies with different substituents and solvent polarities. Complexes 1?a-1?e exhibit relatively strong singlet and triplet transient absorption from 450 to 800?nm, at which point reverse saturable absorption (RSA) could occur. Nonlinear transmission experiments at 532?nm by using nanosecond laser pulses demonstrate that 1?a-1?e are strong reverse saturable absorbers and could potentially be used as broadband nonlinear absorbing materials.     

Mechanism of NO photodissociation in photolabile manganese-NO complexes with pentadentate N5 ligands

The Mn-nitrosyl complexes [Mn(PaPy(3))(NO)](ClO(4)) (1; PaPy(3)(-) = N,N-bis(2-pyridylmethyl)amine-N-ethyl-2-pyridine-2-carboxamide) and [Mn(PaPy(2)Q)(NO)](ClO(4)) (2, PaPy(2)Q(-) = N,N-bis(2-pyridylmethyl)amine-N-ethyl-2-quinoline-2-carboxamide) show a remarkable photolability of the NO ligand upon irradiation of the complexes with UV-vis-NIR light [Eroy-Reveles, A. A.; Leung, Y.; Beavers, C. M.; Olmstead, M. M.; Mascharak, P. K. J. Am. Chem. Soc. 2008, 130, 4447]. Here we report detailed spectroscopic and theoretical studies on complexes 1 and 2 that provide key insight into the mechanism of NO photolabilization in these compounds. IR- and FT-Raman spectroscopy show N-O and Mn-NO stretching frequencies in the 1720-1750 and 630-650 cm(-1) range, respectively, for these Mn-nitrosyls. The latter value for ν(Mn-NO) is one of the highest transition-metal-NO stretching frequencies reported to this date, indicating that the Mn-NO bond is very strong in these complexes. The electronic structure of 1 and 2 is best described as Mn(I)-NO(+), where the Mn(I) center is in the diamagnetic low-spin state and the NO(+) ligand forms two very strong π backbonds with the d(xz) and d(yz) orbitals of the metal. This explains the very strong Mn-NO bonds observed in these complexes, which even supersede the strengths of the Fe- and Ru-NO bonds in analogous (isoelectronic) Fe/Ru(II)-NO(+) complexes. Using time-dependent density functional theory (TD-DFT) calculations, we were able to assign the electronic spectra of 1 and 2, and to gain key insight into the mechanism of NO photorelease in these complexes. Upon irradiation in the UV region, NO is released because of the direct excitation of d(π)_π* → π*_d(π) charge transfer (CT) states (direct mechanism), which is similar to analogous NO adducts of Ru(III) and Fe(III) complexes. These are transitions from the Mn-NO bonding (d(π)_π*) into the Mn-NO antibonding (π*_d(π)) orbitals within the Mn-NO π backbond. Since these transitions lead to the population of Mn-NO antibonding orbitals, they promote the photorelease of NO. In the case of 1 and 2, further transitions with distinct d(π)_π* → π*_d(π) CT character are observed in the 450-500 nm spectral range, again promoting photorelease of NO. This is confirmed by resonance Raman spectroscopy, showing strong resonance enhancement of the Mn-NO stretch at 450-500 nm excitation. The extraordinary photolability of the Mn-nitrosyls upon irradiation in the vis-NIR region is due to the presence of low-lying d(xy) → π*_d(π) singlet and triplet excited states. These have zero oscillator strengths, but can be populated by initial excitation into d(xy) → L(Py/Q_π*) CT transitions between Mn and the coligand, followed by interconversion into the d(xy) → π*_d(π) singlet excited states. These show strong spin-orbit coupling with the analogous d(xy) → π*_d(π) triplet excited states, which promotes intersystem crossing. TD-DFT shows that the d(xy) → π*_d(π) triplet excited states are indeed found at very low energy. These states are strongly Mn-NO antibonding in nature, and hence, promote dissociation of the NO ligand (indirect mechanism). The Mn-nitrosyls therefore show the long sought-after potential for easy tunability of the NO photorelease properties by simple changes in the coligand.     

Absorption Spectra and Photoreactivity of Para-aminobenzophenone by Time-dependent Density Functional Theory

The absorption spectral properties of para-aminobenzophenone (p-ABP) were investigated in gas phase and in solution by time-dependent density functional theory. Calculations suggest that the singlet states vary greatly with the solvent polarities. In various polar solvents, including acetonitrile, methanol, ethanol, dimethyl sulfoxide, and dimethyl formamide, the excited S1 states with charge transfer character result from π→π* transitions. However, in nonpolar solvents, cyclohexane, and benzene, the S1 states are the result of n→π* transitions related to local excitation in the carbonyl group. The excited T1 states were calculated to have ππ* character in various solvents. From the variation of the calculated excited states, the band due to π→π* transition undergoes a redshift with an increase in solvent polarity, while the band due to n→π* transition undergoes a blueshift with an increase in solvent polarity. In addition, the triplet yields and the photoreactivities of p-ABP in various solvents are discussed.     

One-photon photophysics and two-photon absorption of 4-[9,9-di(2-ethylhexyl)-7-diphenylaminofluoren-2-yl]-2,2':6',2'-terpyridine and their platinum chloride complexes

The synthesis, one-photon photophysics and two-photon absorption (2PA) of three dipolar D-π-A 4-[9,9-di(2-ethylhexyl)-7-diphenylaminofluoren-2-yl]-2,2':6',2'-terpyridine and their platinum chloride complexes with different linkers between the donor and acceptor are reported. All ligands exhibit (1)π,π* transition in the UV and (1)π,π*/(1)ICT (intramolecular charge transfer) transition in the visible regions, while the complexes display a lower-energy (1)π,π*/(1)CT (charge transfer) transition in the visible region in addition to the high-energy (1)π,π* transitions. All ligands and the complexes are emissive at room temperature and 77 K, with the emitting excited state assigned as the mixed (1)π,π* and (1)CT states at RT. Transient absorption from the ligands and the complexes were observed. 2PA was investigated for all ligands and complexes. The two-photon absorption cross-sections (σ(2)) of the complexes (600-2000 GM) measured by Z-scan experiment are much larger than those of their corresponding ligands measured by the two-photon induced fluorescence method. The ligand and the complex with the ethynylene linker show much stronger 2PA than those with the vinylene linker.     

Complexation of metal ions, including alkali-earth and lanthanide(III) ions, in aqueous solution by the ligand 2,2',6',2'-terpyridyl

Some metal-ion-complexing properties of the ligand 2,2',6',2'-terpyridyl (terpy) in aqueous solution are determined by following the π-π* transitions of 2 × 10(-5) M terpy by UV-visible spectroscopy. It is found that terpy forms precipitates when present as the neutral ligand above pH ～5, in the presence of electrolytes such as NaClO(4) or NaCl added to control the ionic strength, as evidenced by large light-scattering peaks. The protonation constants of terpy are thus determined at the ionic strength (μ) = 0 to avoid precipitation and found to be 4.32(3) and 3.27(3). The log K(1) values were determined for terpy with alkali-earth metal ions Mg(II), Ca(II), Sr(II), and Ba(II) and Ln(III) (Ln = lanthanide) ions La(III), Gd(III), and Lu(III) by titration of 2 × 10(-5) M free terpy at pH >5.0 with solutions of the metal ion. Log K(1)(terpy) was determined for Zn(II), Cd(II), and Pb(II) by following the competition between the metal ions and protons as a function of the pH. Complex formation for all of these metal ions was accompanied by marked sharpening of the broad π-π* transitions of free terpy, which was attributed to complex formation affecting ligand vibrations, which in the free ligand are coupled to the π-π* transitions and thus broaden them. It is shown that log K(1)(terpy) for a wide variety of metal ions correlates well with log K(1)(NH(3)) values for the metal ions. The latter include both experimental log K(1)(NH(3)) values and log K(1)(NH(3)) values predicted previously by density functional theory calculation. The structure of [Ni(terpy)(2)][Ni(CN)(4)]·CH(3)CH(2)OH·H(2)O (1) is reported as follows: triclinic, P1, a = 8.644(3) ?, b = 9.840(3) ?, c = 20.162(6) ?, α = 97.355(5)°, β = 97.100(5)°, γ = 98.606(5)°, V = 1663.8(9) ?(3), Z = 4, and final R = 0.0319. The two Ni-N bonds to the central N donors of the terpy ligands in 1 average 1.990(2) ?, while the four peripheral Ni-N bonds average 2.107(10) ?. This difference in the M-N bond length for terpy complexes is typical of the complexes of smaller metal ions, while for larger metal ions, the difference is reversed. The significance of the metal-ion size dependence of the selectivity of polypyridyl ligands, and the greater rigidity of ligands based on aromatic groups such as pyridyl groups, is discussed.     

Photo- and protonation-induced changes in structures and physical properties of azo-conjugated metal complex systems

Novel photo- and proton-coupled behavior of azo-conjugated metal complexes is described. The trans-to-cis isomerization of azoferrocene proceeds not only by the photoexcitation of the π-π* transition band but also by photoexcitation of the MLCT (d-π* transition) band, by a protonation-deprotonation cycle (proton-coupled isomerization), and by an oxidation-reduction cycle (redox isomerization). A platinum tolylazophenylenedithiolato complex shows reversible trans-to-cis photoisomerization, protochromism, and novel proton-coupled cis-to-trans isomerization.     

Dinuclear platinum(II) 4,6-diphenyl-2,2'-bipyridine complexes tethered by a rigid bridging ligand: synthesis and photophysics in solution and in LB film

Two dinuclear platinum(II) 4,6-diphenyl-2,2'-bipyridine (C^N^N) complexes (1 and 2) with a rigid bridging ligand cis-1,2-bis(diphenylphosphino)ethylene were synthesized and their photophysical properties were systematically investigated in solution for 1 and 2 and in LB film for 2. Similar to their corresponding mononuclear complexes, both complexes exhibit intense (1)π,π* absorption in the UV region and a broad, moderate absorption band in the visible region, which likely stems from the mixed (1)MLCT (metal-to-ligand charge transfer), (1)ILCT (intraligand charge transfer) and (1)π,π* transitions. Both complexes are emissive in solutions at room temperature and in glassy matrix at 77 K. The emitting state is tentatively assigned as (3)MLCT for 1 and (3)MLCT/(3)ILCT/(3)π,π* for 2 at room temperature. At 77 K, the emission observed for 1 is mainly from the emissive ground-state aggregates, which is concentration dependent; while in 2 the emission from the monomer dominates. Unlike the dinuclear platinum complex with flexible bridging ligand diphenylphosphinoethane, the electronic absorption and emission energies of 1 and 2 at room temperature are independent of their concentration, indicating a fixed conformation for these two complexes. In addition, the presence of alkoxyl substituents on the diphenylbipyridine ligands causes a bathochromic shift of the lowest-energy absorption band and the emission band at room temperature for 2, presumably due to the involvement of the ILCT character into the lowest excited states. The presence of alkoxyl substituents in 2 also makes 2 amphiphilic, allowing for the fabrication of LB films of 2. The electronic absorption and emission characteristics in the LB films of 2 are quite similar to those in solutions, indicating no intermolecular Pt-Pt interactions occur in the LB films. The dinuclear complex without alkoxyl substituent (1) exhibits vapochromic behavior to heteroatom-containing volatile organic compounds (VOC's).     

Experimental and theoretical (INDO CI) electronic absorption spectroscopy in the examination of tautomeric phenomena in nitracrine and its nitre isomers

Electronic absorption spectroscopy was employed to examine tautomeric phenomena in N,N-dimethyl-N-(1-nitro-9-acridinyl)-1,3-propanediamine (known as nitracrine—WHO, or Ledakrin in Poland) which exhibits antitumour activity, and also to examine its three nitro isomers. The analysis of the experimental absorption spectra reveals that the compounds exist in the liquid-phase in at least two forms (most probably amino and imino tautomeric forms), remaining in an equilibrium which is strongly affected by the features of a solvent. This was qualitatively confirmed by examining frequencies and oscillator strengths of electronic transitions obtained for the lowest energy structures of a given form by two independent methods based on INDO approximation. The latter methods predict that the strongest transitions occurring below 280 nm have a π→π* origin, whereas the longest wavelength transitions may be either π→π* or n→π* type and cause a shift in electron density within the acridine aromatic system and attached nitro group and exocyclic nitrogen atom.     

Calculated optical spectrum of model oxyheme complex

The optical spectrum of a model oxyheme complex has been calculated using a new intermediate neglect of differential overlap (INDO-SCF-CI ) method that allows for the inclusion of configuration interaction and transition metals. In addition to the porphyrin π→π* transitions common to all heme proteins, four weak x,y polarized transitions observed only in oxyheme complexes have been calculated and assigned to excitations involving the lowest-empty highly delocalized (Oπ, dπ) orbital. Two broad z-polarized bands observed in the single-crystal polarized absorption spectra of oxymyoglobin and hemoglobin have also been calculated. Controversy exists over the assignment of these transitions and, in particular, over the extent of involvement of the oxygen ligand. Our calculations assign the weaker near-IR visible band mainly to the d σ dπ→ dπ* excitations and the more intense UV band mainly to a_2u → dσ* excitations. While significant participation (25%) of the highly delocalized (Oπ, dπ) virtual orbital is also found, these z-polarized transitions need not be totally unique to oxyheme complexes, in keeping with experimental observation.     

Computational Photochemistry of the Azobenzene Scaffold of Sudan I and Orange II Dyes: Excited‐State Proton Transfer and Deactivation via Conical Intersections

We employed the complete active space self‐consistent field (CASSCF) and its multistate second‐order perturbation (MS‐CASPT2) methods to explore the photochemical mechanism of 2‐hydroxyazobenzene, the molecular scaffold of Sudan I and Orange II dyes. It was found that the excited‐state intramolecular proton transfer (ESIPT) along the bright diabatic ¹ππ* state is barrierless and ultrafast. Along this diabatic ¹ππ* relaxation path, the system can jump to the dark ¹nπ* state via the ¹ππ*/¹nπ* crossing point. However, ESIPT in this dark state is largely inhibited owing to a sizeable barrier. We also found two deactivation channels that decay ¹ππ* keto and ¹nπ* enol species to the ground state via two energetically accessible S₁/S₀ conical intersections. Finally, we encountered an interesting phenomenon in the excited‐state hydrogen‐bonding strength: it is reinforced in the ¹ππ* state, whereas it is reduced in the ¹nπ* state. The present work sets the stage for understanding the photophysics and photochemistry of Sudan I–IV, Orange II, Ponceau 2R, Ponceau 4R, and azo violet.     

Exploratory studies on coordination chemistry of a redox-active bridging ligand: synthesis, properties and solid state structures of the complexes

The explorative coordination chemistry of the bridging ligand TTF-PPB is presented. Its strong binding ability to Co(II) and then to Ni(II) or Cu(II) in the presence of hexafluoroacetylacetonate (hfac(-)), forming new mono- and dinuclear complexes 1-3, is described. X-ray crystallographic studies have been conducted in the case of the free ligand TTF-PPB as well as its complexes [Co(TTF-PPB)(hfac)(2)] (1) and [Co(hfac)(2)(μ-TTF-PPB)Ni(hfac)(2)] (2). Each metal ion is bonded to two bidentate hfac(-) anions through their oxygen atoms and two nitrogen atoms of the PPB moiety with a distorted octahedral coordination geometry. Specifically, nitrogen donor atoms of TTF-PPB adopt a cis-coordination but not in the equatorial plane, which is quite rare. Electronic absorption, photoinduced intraligand charge transfer ((1)ILCT), and electrochemical behaviour of 1-3 have been investigated. UV-Vis spectroscopy shows very strong bands in the UV region consistent with ligand centred π-π* transitions and an intense broad band in the visible region corresponding to a spin-allowed π-π* (1)ILCT transition. Upon coordination, the (1)ILCT band is bathochromically shifted by 3100, 6100 and 5900 cm(-1) on going from 1 to 3. The electrochemical studies reveal that all of them undergo two reversible oxidation and one reversible reduction processes, ascribed to the successive oxidations of the TTF moiety and the reduction of the PPB unit, respectively.     

Modification of the Optical Spectrum of Cytosine by the Formation of an Ordered Monolayer of Molecules at a Au(110)/Electrolyte Interface

An analysis of the reflection anisotropy spectrum (RAS) of an ordered monolayer of cytosine adsorbed at a Au(110)/electrolyte interface is found to contain optical contributions from both the substrate and the cytosine. The spectrum of cytosine in an aqueous environment is significantly broadened by the interaction between the molecule and the Au(110). Successful simulations of the Au(110)/cytosine interface consisting of two additional molecular transitions, which sit in the middle of previously observed molecular absorption bands, are produced by an empirical Lorentzian transition model that is consistent with previous theoretical and experimental studies. While this analysis alone cannot determine the number of π→π* dipole transitions, it confirms that the only cytosine transitions that contribute to the optical response of the Au(110)/cytosine interface are located in the plane of the molecule, which is vertical to the gold surface with the long axis along the [1$\bar 1$ 0] direction.     

Density Functional Studies on Isonicotinato Lead(II) Complex [Pb(C5H4NCOO)2]

1 INTRODUCTION Recently, the chemistry of lead is of interest in relation to its toxicity and effects on intelligence in human populations[1~3]. The design of drugs to coun- teract the effects of lead poisoning requires estab- lishing the preferred ligands of Pb(II) and their ste- reochemistry. Consequently, synthesis of chelated- form antidotes for lead(II) ion toxicosis has attracted more and more attention, and numerous reports con- cerning experimental coordination chemistry of lead(…     

Synthesis,Crystal Structure,Characterizationand Quantum Chemical Studies on 1N-Acetyl-3-（2,4-dichloro-5-fluorophenyl）-5-（p-methyl-phenyl）-2-pyrazoline

1N-Acetyl-3-（2,4-dichloro-5-fluoro-phenyl）-5-（p-methyl-phenyl）-2-pyrazoline has been synthesized and characterized by elemental analysis, IR, UV-Vis and X-ray single-crystal diffraction. Ab intio calculations have been carded out for the compound by using both B3LYP and HF methods at the 6-31G^＊ basis set. The calculated results show that the predicted geometry can well reproduce the structural parameters. The electronic absorption spectra calculated by B3LYP/6-31G^＊ method are approximate to the experiments and the Natural Bond Orbital （NBO） analyses suggest that the above electronic transitions are mainly assigned to n→π^＊ and π→π^＊ transitions. CIS-HF/6-31G^＊ method is not suitable to predict the electronic spectra for the title compound. The calculation of the second order optical nonlinearity was carded out, giving the value of molecular hyperpolarizability equal to 2.194^＋ 10^-30 esu. On the basis of vibrational analyses, the thermodynamic properties of the compound at different temperature have been calculated, revealing the correlation between C p, m^0, S m^0, H m^0 and temperature.     

6-N,N-二甲基腺嘌呤激发态结构动力学的共振拉曼光谱

采用共振拉曼光谱技术和密度泛函理论方法研究了6-N,N-二甲基腺嘌呤(DMA)的A带和B带电子激发和Franck-Condon 区域结构动力学. π_H→π_L^*跃迁是A带吸收的主体, 其振子强度约占整个A带吸收的79%.由弥散轨道参与的n→Ryd 和π_H→Ryd 跃迁在B带跃迁中扮演重要角色, 其振子强度约占B带吸收的62%,而在A带吸收中占主导的π_H→π_L^*跃迁的振子强度在B带吸收中仅占33%. 嘌呤环变形伸缩+C8H/N9H面内弯曲振动ν₂₃和五元环变形伸缩+C8H弯曲振动ν₁₃的基频、泛频和合频占据了A带共振拉曼光谱强度的绝大部分, 说明¹π_Hπ_L^*激发态结构动力学主要沿嘌呤环的变形伸缩振动, N9H/C8H/C2H弯曲振动等反应坐标展开, 而ν₁₀, ν₂₉, ν₂₁, ν₂₆和ν₄₀的基频、泛频和合频占据了B带共振拉曼光谱强度的主体部分, 它们决定了B带激发态的结构动力学. A带共振拉曼光谱中ν₂₆和ν₁₂被认为与1nπ*/1ππ*势能面锥型交叉有关. B带共振拉曼光谱中ν₂₁的激活与¹ππ^*/¹πσ_N9H^*势能面锥型交叉相关.     

Spectral and Electrochemical Characterization of Dibenzotetraaza[14]annulenes

The UV/Vis absorption spectra and cyclic voltammograms (CV) of the Cu(II) and Ni(II) complexes of γ,γ'-alkoxycarbonyl derivatives of α,α'- diphenyldibenzo-tetraaza[14]annulene are analyzed and compared. The observed ratio of absorption intensities at the peaks of π-π* transitions is linearly correlated with the difference of HOMO and LUMO energy levels of the substituents. Moreover, the measured values of the mid-peak potential of metal redox reactions on a Pt electrode in DMF are linearly correlated with the ionization potential values of the appropriate substituents.