Mechanisms of reactive oxygen species photogeneration by benzo[a]pyrene: A DFT study

Benzo[a]pyrene (BaP) possesses photosensitive activity and can photogenerate reactive oxygen species (ROS), which have been postulated to be involved in the BaP induced oxidative DNA damage. Therefore, in the present work, a thermodynamic analysis on the ROS-photogenerating mechanisms of BaP was performed on the basis of quantum chemical calculations. It was revealed that: (i) the ¹O₂-generating pathway involves direct energy transfer from triplet excited state BaP to ³O₂ both in benzene and water; (ii) BaP gives birth to O₂^? through two pathways in water, i.e., electron transfer from triplet excited state BaP or anion radical of BaP to ³O₂.     

Role of the intermolecular and intramolecular hydrogen bonding on the excited-state proton transfer behavior of 3-aminophthalimide (3AP) dimer

In this work, both the intermolecular and intramolecular hydrogen bonding of 3-aminophthalimide (3AP) dimer complex in the electronically excited state have been investigated theoretically using the time-dependent density functional theory (TDDFT) method. The calculated infrared spectrum of the hydrogen-bonded 3AP dimer complex for the S₁ state shows that the CO and H–N bonds involved in the intramolecular hydrogen bond C₃O₅?H₈–N₆ and intermolecular hydrogen bond C₁O₄?H_7′–N_2′ which are markedly red-shifted compared with those predicted for the ground state. The calculated length of the two hydrogen bonds C₃O₅?H₈–N₆ and C₁O₄?H_7′–N_2′ are significantly shorter in S₁ state than in the ground state. However, the bond lengths of the intramolecular hydrogen bond C_3′O₅?H_8′–N_6′ and intermolecular hydrogen bond C_1′O_4′?H₇–N₂ nearly unchanged upon electronic excitation to the S₁ state. Thus, the intramolecular hydrogen bond C₃O₅?H₈–N₆ and intermolecular hydrogen bond C₁O₄?H_7′–N_2′ of the hydrogen-bonded 3AP dimer complex are stronger in the electronically excited state than in the ground state. Moreover, it has been demonstrated that the excited-state proton transfer reaction is facilitated by the electronic excited-state hydrogen bond strengthening.     

Effects of zero point vibration on the reaction dynamics of water dimer cations following ionization

Reactions of water dimer cation following ionization have been investigated by means of a direct ab initio molecular dynamics method. In particular, the effects of zero point vibration and zero point energy (ZPE) on the reaction mechanism were considered in this work. Trajectories were run on two electronic potential energy surfaces (PESs) of : ground state (²A″‐like state) and the first excited state (²A′ ‐ like state). All trajectories on the ground‐state PES lead to the proton‐transferred product: H₂O⁺(Wd)‐H₂O(Wa) → OH(Wd)‐H₃O⁺(Wa), where Wd and Wa refer to the proton donor and acceptor water molecules, respectively. Time of proton transfer (PT) varied widely from 15 to 40 fs (average time of PT = 30.9 fs). The trajectories on the excited‐state PES gave two products: an intermediate complex with a face‐to‐face structure (H₂O‐OH₂)⁺ and a PT product. However, the proton was transferred to the opposite direction, and the reverse PT was found on the excited‐state PES: H₂O(Wd)‐H₂O⁺ (Wa) → H₃O⁺(Wd)‐OH(Wa). This difference occurred because the ionizing water molecule in the dimer switched between the ground and excited states. The reaction mechanism of and the effects of ZPE are discussed on the basis of the results. © 2017 Wiley Periodicals, Inc.     

A CI pseudopotential-based description of the low-lying states of Ag O2

Extensive SCF -LCAO -MO variational and perturbative configuration interaction (CI ) calculations framed within an effective core potential approximation have been performed to determine the two experimentally observed geometrical isomers of A_g O₂ and the interconversion route between them. These structural forms, associated to the ground-state local minima, yield virtually the same energy, and their spontaneous interconversion is strongly indicated, which agrees fairly well with the experimental measurements. The reaction A_g + O₂ → A_g O₂ was theoretically analyzed along a CI fully optimized energy pathway for the ground and various excited states, within C_2v and C_s symmetry. Although a tight-ion pair (A O) character is predicted for the ground state at the equilibrium geometries, its dissociation leads to neutral rather than to ionic fragments. The study of the reaction path within C_s symmetry shows an avoided crossing between the ground state and another ²A″ potential curve where the former correlates adiabatically with the reactants A_g(²S) + O₂(¹Δ_g). This indicates that the formation of the complex proceeds via a reactive state of molecular oxygen. The higher ²A″ electronic curves correlate with the metal ²P excited state, and the oxygen binding is found to be less favorable. The present results are shown to have an important bearing on the experimentally known catalytic properties of oxygen adsorbed on silver surfaces.     

Construction and applications of symmetrized valence bond wave functions

A method constructing symmetry-adapted bonded Young tableau bases is proposed, based on the symmetry properties of bonded tableaus and the projection operator associated with a point group. Several examples including the ground states and π excited states of O₃⁻, O₃, O₃⁺, and C₃⁻ are shown for instruction to construct the symmetrized valence bond (VB) wave function. Excitation energies of transitions from the ground states to π excited states of O₃⁻, C₃H₅, and C₃⁻ are calculated with an optimized symmetrized valence bond wave function in the σ–π separation approximation. Good agreement between the VB and experimental excitation energies is observed. The bonding features of the ground state and the first π excited singlet and triplet states for S₃ are discussed according to bonding populations from VB calculations. Both the singlet-biradical and the dipole structures have significant contributions to the ground state X ¹A₁ of S₃, while the excited state 1 ¹B₂ is essentially composed of the dipole structures, and the 1 ³B₂ excited state is comprised from a triplet-biradical structure. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 66 : 1–7, 1998     

The Origin of the Reactivity of the Criegee Intermediate: Implications for Atmospheric Particle Growth

The electronic structure of the simplest Criegee intermediate, H₂COO, is practically that of a closed shell. On the biradical scale (β), where 0 corresponds to the pure closed shell and 1 to a pure biradical, its β value is only 0.10, suggesting that its ground electronic state is best described as a H₂C=O^δ+?O^δ? zwitterion. However, this picture of a nearly inert closed shell contradicts its rich reactivity in the atmosphere. It is shown that the mixing of its ground state with the first triplet excited state, which is a pure biradical state of the type H₂C^.?O?O^., is responsible for the formation of strongly bound products during reactions inducing atmospheric particle growth.     

Orthogonally aligned cyclic BODIPY arrays with long-lived triplet excited states as efficient heavy-atom-free photosensitizers

In photosensitizers, long triplet excited state lifetimes are key to their efficient electron transfer or energy transfer processes. Herein, we report a novel class of cyclic trimeric BODIPY arrays which were efficiently generated from easily accessible meso-mesityldipyrrinone and arylboronic acids in one pot. Arylboronic acid, for the first time, was used to provide a boron source for BODIPY derivatives. Due to the well-defined and orthogonally aligned BODIPY cores as verified by X-ray crystallography, these BODIPY arrays show strong exciton coupling effects and efficient intersystem crossings, and are novel heavy-atom-free photosensitizers with a long-lived triplet excited state (lifetime up to 257.5 μs) and good reactive oxygen species generation efficiency (up to 0.72) contributed by both ¹O₂ and O₂⁻˙ under light irradiation.

Cyclic BODIPY trimers showed strong exciton coupling in singlet excited states and long-lived triplet excited states, and generated both singlet oxygen and superoxide radicals under light irradiation, giving good reactive oxygen quantum yields and promising PDT results in vitro.     

Nonempirical Investigation of Equilibrium Geometry and Electronic Structure of Kynurenine and 3-Hydroxykynurenine Molecule

By Hartree-Fock-Roothaan method with complete geometry optimization in the basis 6-31G* ab initio calculations of equilibrium geometry and electronic structure were performed for kynurenine C₁₀H₁₂N₂O₃ and 3-hydroxykynurenine C₁₀H₁₂N₂O₃ molecules in the singlet ground state and the first triplet excited state. The molecules in the triplet state can react at the oxygen of the carbonyl group adjacent to the aromatic ring by quite different pathway compared to the molecules in the ground singlet state.     

Density functional theory study of the photosensitization mechanisms of indigo

The triplet excited state properties and photosensitization mechanisms of indigo were investigated based on density functional theory calculations. The solvent effects on the photosensitization mechanisms of indigo have also been considered. The thermodynamic feasibility of the possible ¹O₂ and O₂·⁻-photogeneration pathways by triplet excited state indigo in different solvents was explored, in order to gain some deeper insights into the photosensitization characters of the dye.      

Photoactivation mechanism of orthovanadate-like (V=O)O3 species

The photoluminescence spectrum and action spectrum for the photooxidation of orthovanadate-like (V=O)O₃ species exhibiting photoluminescence at 520 nm indicate that the triplet excited state T₁ of the orthovanadate-like species, which is formed from the singlet excited states S₁ and S₂ by intersystem crossing, is directly involved in the photooxidation of cyclohexane into cyclohexanone in the presence of molecular oxygen.     

Triplet Energy of 2, 2-Dimethylisoindene from Electron-Energy-Loss Spectroscopy and Photoinduced Triplet Energy Transfer

The excited electronic states of 2, 2-dimethylisoindene ( 1 ) have been studied by electron-energy-loss spectroscopy. Its vertical gas-phase triplet (1³B₂), and singlet (1¹B₂) excitation energies are 1.61 and 3.19 eV, respectively. The excited states are thus lowered by 0.49 eV and 1.21 eV, respectively, when compared to the corresponding states of (all-E)-octatetraene, which serves as a reference compound. These shifts are partially reproduced by ZINDO calculations. The spectra give no evidence for a 2¹A_g state below the 1¹B₂ state, but this lack of observation does not exclude its existence. The lowest triplet state T₁( 1 ) was further characterized by flash photolysis. T₁( 1 ) was observed as a transient intermediate, λ ≤ 350 nm, with a lifetime of 8 m?s in degassed hexane. The adiabatic excitation energy of T₁( 1 ) was bracketed to the range of 1.1 ± 0.1 eV by energy-transfer experiments. Relationships between the energies of the lowest excited singlet and triplet states of 1 and the lowest excited doublet state of its radical cation ${1}^{+\kern0pt {.}}$ – essentially a non-Koopmans' state – are discussed.     

Excited States of Weak Interacting Complexes of Formaldehyde and Alkali Metal Ions

The electronically excited states of formaldehyde and its complexes with alkali metal ions are investigated with the time-dependent density functional theory (TD DFT) method. Vertical transition energies for several singlet and triplet excited states, adiabatic transition energies for the first singlet and triplet excited states S₁ and T₁, the adiabatic geometries and vibrational frequencies of the ground state S₀ and the first singlet and triplet excited states S₁ and T₁ for formaldehyde and its complexes are calculated. Better agreement with the experiment than that of the CIS method is obtained for CH₂O at the TD DFT level. The nonlinear C=O?M⁺ interaction in the excited states S₁ and T₁ is weaker than the linear interaction in the ground state. In the S₀ and S₁ states, the C=O bond is elongated by cation complexation and its stretching frequency is red-shifted, but in the T₁ state the C=O bond is shortened and its frequency is blue-shifted.     

The reaction of O(3P) with C2HCl3

The reaction of O(³P), prepared from the Hg photosensitization of N₂O, with C₂HCl₃ was studied at 25°C. The products of the reaction in the absence of O₂ were CO, CHCl₃, and polymer (as well as N₂ from the N₂O). The quantum yields of CO and CHCl₃ were 0.23 ± 0.01 and 0.14 ± 0.05, is respectively independent of reaction conditions. The reaction mechanism is with k_14a/k₁₄ = 0.23, where k_14a + k_14b. Most of the HCl and CCl₂ combine to form CHCl₃, but some other products must also be formed to account for the difference in the CO and CHCl₃ quantum yields. The C₂HCl₃O* adduct polymerizes without involving additional C₂HCl₃ molecules, since the quantum yield of C₂HCl₃ disappearance, ? Φ{C₂HCl₃}, was about 1.0 at high values of [N₂O]/[C₂HCl₃]. The rate coefficient for the reaction of O(³P) with C₂HCl₃ is 0.10 that for the reaction of O(³P) with C₂F₄. In the presence of O₂ the free radical chain oxidation occurs because of the reaction The main product is CHCl₂CCl(O) with smaller amounts of CO and CCl₂O, and some CO₂. The chain lengths were long and values of ? Φ {C₂HCl₃} up to 90 were observed.     

Solvent free mechanochemical oxygenation of fullerene under oxygen atmosphere

Oxygenation of fullerene took place under mechanical stressing by a simple vibration mill in an oxygen atmosphere at 1 atm. Milled products were mixtures of poly-oxidized fullerene, C₆₀O_n, containing C-O-C and CO bonds. We observed a concurrent reaction as well, that is, polymerization of C₆₀ and C₆₀O. The average number of oxygen, n, of the overall products obtained by milling for 5 h was 8.6 per molecule of C₆₀. We confirmed generation of singlet oxygen during the present mechanochemical reaction by an ESR spin trapping method. Trapping of ¹O₂ was completely inhibited the oxygenation of fullerene. Formation of ¹O₂ is attributed to the energy transfer from mechanically excited state of fullerene and plays a decisive role on the present oxygenation of fullerene under mechanical stressing in O₂. In contrast, no ¹O₂ was observed by mechanically stressing the conventional photo-sensitizer, rosebengal. The difference in the behavior of C₆₀ and rosebengal is interpreted in terms of molecular deformation, being much easier for a 3D molecule, C₆₀, than a planar molecule, in line with the concept of inverse Jahn-Teller effects.     

Synthesis and dehydration of double oxalates of rare earths(III) with some monovalent metals

Double oxalates of rare earths(III) and rubidium with the general formulae RbCe(C₂O₄)₂ 4.5H₂O, RbLn(C₂O₄)₂4H₂O (Ln=Yb, Lu), RbLn(C₂O₄)₂·3.5H₂O (Ln=La, Pr-Dy), and RbLn(C₂O₄)₂·3H₂O (Ln=Ho, Er, Tm, Y) were synthesized. They were characterized by chemical analysis, TG, DTG and DSC over the temperature interval 20–500C and X-ray powder diffraction examination. At the chosen final temperature (500C), either oxide (Ln₂O₃) or basic carbonate Ln₂O₂CO₃) and Rb₂CO₃ were obtained, depending on the rare earth(III) element. On the basis of the X-ray diffraction patterns, the isolated compounds can be divided into five isostructural groups.     

Potential energy surfaces of carbon dioxide

Several bent valence states of CO₂ are characterized by means of full-valence-space MCSCF calculations. The ground state potential energy surface exhibits a double well corresponding to a ring minimum, with C_2vsymmetry (¹A₁) and a 73.1° OCO angle, in addition to the linear (¹σ) global minimum. The transition state for the ring opening process, which has a barrier of 12.1 kcal/mole with respect to the ring minimum, is however found to have C_s symmetry. Double minima are also shown to exist for the ¹A₂, ¹B₁ and ¹B₂ excited states. However, in these cases all minima are bent. Cross sections through the ground state potential energy surface corresponding to the two collinear exchange reactions O(¹D) + CO(¹σ⁺) → OC(¹σ⁺) + O(¹D) C(³P) + O₂(³σ) → CO(¹σ⁺) + O(¹D) are also calculated and their energy contour maps are reported. The latter reveals the existence of a stable linear intermediate with the structure COO. © 1994 John Wiley & Sons, Inc.     

Ab initio CI study of the nitric oxide dimer (N2O2)

Configuration interaction (CI) studies of the ground and electronically excited states are reported for nitric oxide dimer (N₂O₂) in itscis equilibrium geometry. The lowest triplet state (³ B ₂) is found to lie only 0.43 eV above the ground state (¹ A ₁). The¹ A ₁ ¹ B ₁ transition is shown to be responsible for the rising absorption in the near infrared region observed experimentally. The transition of¹ A ₁¹ A ₂ calculated in the visible spectrum range of 701 nm (1.77 eV) is symmetry forbidden.     

Energy‐Funneling‐Based Broadband Visible‐Light‐Absorbing Bodipy–C60 Triads and Tetrads as Dual Functional Heavy‐Atom‐Free Organic Triplet Photosensitizers for Photocatalytic Organic Reactions

C₆₀–bodipy triads and tetrads based on the energy‐funneling effect that show broadband absorption in the visible region have been prepared as novel triplet photosensitizers. The new photosensitizers contain two or three different light‐harvesting antennae associated with different absorption wavelengths, resulting in a broad absorption band (450–650 nm). The panchromatic excitation energy harvested by the bodipy moieties is funneled into a spin converter (C₆₀), thus ensuring intersystem crossing and population of the triplet state. Nanosecond time‐resolved transient absorption and spin density analysis indicated that the T₁ state is localized on either C₆₀ or the antennae, depending on the T₁ energy levels of the two entities. The antenna‐localized T₁ state shows a longer lifetime (τ_T=132.9 μs) than the C₆₀‐localized T₁ state (ca. 27.4 μs). We found that the C₆₀ triads and tetrads can be used as dual functional photocatalysts, that is, singlet oxygen (¹O₂) and superoxide radical anion (O₂ ^{. ?}) photosensitizers. In the photooxidation of naphthol to juglone, the ¹O₂ photosensitizing ability of the C₆₀ triad is a factor of 8.9 greater than the conventional triplet photosensitizers tetraphenylporphyrin and methylene blue. The C₆₀ dyads and triads were also used as photocatalysts for O₂ ^{. ?}‐mediated aerobic oxidation of aromatic boronic acids to produce phenols. The reaction times were greatly reduced compared with when [Ru(bpy)₃Cl₂] was used as photocatalyst. Our study of triplet photosensitizers has shown that broadband absorption in the visible spectral region and long‐lived triplet excited states can be useful for the design of new heavy‐atom‐free organic triplet photosensitizers and for the application of these triplet photosensitizers in photo‐organocatalysis.     

9,9-二己基芴基四乙炔基聚炔铂的合成及发光性质

Soluble platinum(Ⅱ)polyyne polymers trans-{Pt-[P(C_4H_8N)_3]_2(C≡C)_2R(C≡C)_(2-)}_n and trans-{Pt-[P(C_4-H_3O)_3]_2(C≡C)_2R(C≡C)_(2-)}_n(R=9,9-dihexylfluorene-2,7-diyl)have been prepared in good yields by CuI-catalyzedpolymerization involving the dehydrohalogenating coupling of trans-{PtCl_2[P(C_4H_8N)_3]_2} and trans-{PtCl_2[P-(C_4H_3O)_3]_2} with H(C≡C)_2R(C≡C)_2H,respectively.We report the optical spectroscopy of these polyplatinaynes.The influence of the heavy metal atom in these metal alkynyl systems on the intersystem crossing rate and the spa-tial extent of lowest singlet and triplet excitons was systematically characterized.Our investigations indicate that theorganic triplet emissions can be harvested by the heavy-atom effect which enables efficient intersystem crossingfrom the S_1 singlet excited state to the T_1 triplet excited state.     

A theoretical study on the red- and blue-shift hydrogen bonds of cis-trans formic acid dimer in excited states

The excited states of cis-trans formic acid dimer and its monomers have been investigated by time-dependent density functional theory (TDDFT) method. The formation of intermolecular hydrogen bonds O₁-H₁...O₂=C₂ and C₂-H₂...O₄=C₁ induces bond length lengthening of the groups related to the hydrogen bond, while that of the C₂-H₂ group is shortened. It is demonstrated that the red-shift hydrogen bond O₁-H₁...O₂=C₂ and blue-shift hydrogen bond C₂-H₂...O₄=C₁ are both weakened when excited to the S₁ state. Moreover, it is found that the groups related to the formation of red-shift hydrogen bond O₁-H₁...O₂=C₂ are both strengthened in the S1 state, while the groups related to the blue-shift hydrogen bond C₂-H₂...O₄=C₁ are both weakened. This will provide information for the photochemistry and photophysical study of red- and blue-shift hydrogen bond.