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A better knowledge of the structure of the electronically excited state of substrates is indispensable for the understanding and optimization of . For this study, triplet energies of a variety of α,β-unsaturated γ-lactones (furanones) as well as the structures of the vibrationally relaxed triplet state (T1) have been determined using ab initio coupled-cluster (CCSD) method and/or density functional theory (DFT) calculation. A twist of the original planar structure around C = C bond is found in the relaxed triplet state, π-π*. In the 5-membered ring of furanones the contribution of this mode is limited and the pyramidalization in the C4 position also contributes to the stabilization. The contribution of each stabilization mode is characterized by the dihedral angles and the Mulliken atomic spin densities. The substituent effect on the pyramidalization and the spin density distribution in the C4 and in the C5 position are reported. Depending on the substitution in the C4 position, the orientation of the pyramidalization is either favored syn or anti with respect of the hydroxyl substituent in the C5 position. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Basing on the experimental data, it has been shown that for EХ (E = N, P, As, or Sb; X = F, Cl, Br, I, CH, СН, or SiH) compounds the value of the difference between first ionization potentials of atoms and molecules is a function of the bond angle and dipole moment of the molecule. The calculated values of dipole moments of charged atoms and groups are regularly changed within the considered compounds series. The change of the dipole moment of the molecules during the vibrational excitation has been determined, and intensities of symmetric stretching and deformation bands in IR spectra of EF and ECl compounds have been estimated. [ABSTRACT FROM AUTHOR]

The photoelectrical properties of two dyes--ethyl red and carminic acid--as sensitizers of dye-sensitized solar cells were investigated in experiments herein described. In order to reveal the reason for the difference between the photoelectrical properties of the two dyes, the ground state and excited state properties of the dyes before and after adsorbed on TiO2 were calculated via density functional theory (DFT) and time-dependent DFT (TDDFT). The key parameters including the light harvesting efficiency (LHE), the driving force of electron injection (ΔGinject) and dye regeneration (ΔGregen), the total dipole moment (μnormal), the conduction band of edge of the semiconductor (ΔECB), and the excited state lifetime (τ) were investigated, which are closely related to the short-circuit current density (Jsc) and open circuit voltage (Voc). It was found that the experimental carminic acid has a larger Jsc and Voc, which are interpreted by a larger amount of dye adsorbed on a TiO2 photoanode and a larger ΔGregen, excited state lifetime (τ), μnormal, and ΔECB. At the same time, chemical reactivity parameters illustrate that the lower chemical hardness (h) and higher electron accepting power (ω+) of carminic acid have an influence on the short-circuit current density. Therefore, carminic acid shows excellent photoelectric conversion efficiency in comparison with ethyl red. [ABSTRACT FROM AUTHOR]

The structure-properties relationships of copolymer involving N-vinylcarbazole (PVK) and poly (p-phenylene-vinylene) ( PPV) blocks, denoted PVK–PPV, was investigated by calculations based on density functional theory (DFT) and completed by experimental analyses. Thus, vibrational, optical and emission spectra of model compound have been simulated and compared to the experiments observations published recently. Ionization potentials (IPs), electron affinities (EAs) and energy gaps were determined. Furthermore, quantum yields, radiative and nonradiative exciton lifetime was highlighted. [ABSTRACT FROM AUTHOR]

The structural and photophysical properties of four heteroleptic Iridium (III) complexes, based on 1-phenylpyrazole ligand, have been investigated theoretically. The effect of chemical substitution on the absorption and the emission spectra of the complexes has been studied and compared with the experimental data. We observe a significant structural change in the lowest triplet excited state as compared to the ground singlet state. We compute the emission wavelength of the complexes by considering the spin-orbit coupling. Using these understandings, we predict two new complexes having deeper blue emission which are supposed to be better efficient OLED materials. [ABSTRACT FROM AUTHOR]

The analysis of electron structure of yttrium(III) complexes with cinnamic and quinaldic acids was carried out. Electron transitions were assigned, and influence of the nature of frontier orbitals on the position of absorption bands in the electron spectra was revealed. The TD-DFT calculation has shown that different ratios of intensities of π- π* and n- π* bands in the electron absorption spectra of the compounds are caused by different natures of frontier orbitals of the complexes. It was found that dipole moments of both complexes increase upon photoexcitation, greater changes being observed in Y(III) quinaldate. The reason of the greater Stokes shift of Y(III) quinaldate was established. [ABSTRACT FROM AUTHOR]

The results of quantum yield (QY) study of tryptophanyl glutamate (Trp–Glu), tryptophanyl lysine (Trp–Lys) and lysinyl tryptophan (Lys–Trp) dipeptides over the pH range, 1.5–13, show that the charge state of the N-terminal amine, and not the nominal molecular charge determines the QY. When the terminal amine is protonated, QY is low (10 −2 ) for all three dipeptides. As the terminal amine cation is found proximal to the indole ring in Trp–Glu and Trp–Lys conformers but not in those for Lys–Trp, its effect may lie only in the partitioning of energy between nonradiative processes, not on QY reduction. QY is also low when both the N-terminal amine and indole amine are deprotonated. These two low QY states can be distinguished by fluorescence lifetime measurement. Molecular dynamics simulation shows that the Chi 1 conformers persist for tens of nanoseconds such that 10 0 –10 1 ns lifetimes may be associated with individual Chi 1 conformers. The ground state electron density or isosurface of high QY (0.30) 3-methyindole has a uniform electron density over the indole ring as do the higher QY Trp dipeptide conformers. This validates the association of ground state isosurfaces with QY. Excited state orbitals from calculated high intensity, low energy absorption transitions are typically centered over the indole ring for higher QY dipeptide species and off the ring in lower QY species. Thus excited state orbitals substantiate the earlier finding that the ground state isosurface charge density pattern on the indole ring can be predictive of QY. [ABSTRACT FROM AUTHOR]

• The geometry changes of the tgt - and the ttt -rotamer of 1,2-diphenoxyethane have been determined from a combined fit of rotation al constants and fluorescence emission intensities from several vibronic bands. • The geometry changes are compared to the results of ab initio calculations at the spin-component-scaled approximate coupled cluster singles and doubles (CC2) level of theory. • The excitonic splitting of the origins of both rotamers has been determined from ab initio calculations. The geometry changes of the tgt - and the ttt -rotamer of 1,2-diphenoxyethane were determined from a combined fit of line intensities in fluorescence emission spectra, obtained via pumping different vibronic transition, and the changes of rotational constants upon electronic excitation, which were taken from [E.G. Buchanan, P.S. Walsh, D.F. Plusquellic, T.S. Zwier, J. Chem. Phys. 138 (2013) 204313]. The so determined geometry changes are compared to the results of ab initio spin-component-scaled approximate coupled cluster singles and doubles (SCS-CC2) calculations. [ABSTRACT FROM AUTHOR]

Photoenzymes use light to initiate biochemical reactions. Although rarely found in nature, their study has advanced understanding of how light energy can be harnessed to facilitate enzyme catalysis, which is also of importance to the design and engineering of man-made photocatalysts. Natural photoenzymes can be assigned to one of two families, based broadly on the nature of the light-sensing chromophores used, those being chlorophyll-like tetrapyrroles or flavins. In all cases, light absorption leads to excited state electron transfer, which in turn initiates photocatalysis. Reviewed here are recent findings relating to the structures and mechanisms of known photoenzymes. We highlight recent advances that have deepened understanding of mechanisms in biological photocatalysis. [ABSTRACT FROM AUTHOR]

The efficiency and mechanism of heterogeneous catalytic O 3 and UV/O 3 for municipal solid waste (MSW) incineration leachate advanced treatment was systematically compared. Prior to comparison, catalyst used in heterogenous catalytic O 3 and operation parameters for each technology were optimized. The COD removal of CuO@Al 2 O 3 /O 3 under its optimal parameters was 57.2%, which failed to meet the standard (≥75%). In contrast, the COD removal by UV/O 3 could be 82.3%. The superior efficiency of UV/O 3 over CuO@Al 2 O 3 /O 3 could be summarized into three aspects: (I) Cu bounded ·OH (≡Cu–O·) preferentially attacked hydrophilic groups, while free hydroxyl radical (·OH) was non-selective, thus UV/O 3 exhibited a unique three-stage mechanism; (II) The oxidation potential of ≡Cu–O· was higher than that of ·OH, therefore was more vulnerable to the negative effect of radical self-quenching; (III) The existence of UV-induced excited states made organics in UV/O 3 more active than in CuO@Al 2 O 3 /O 3 system, thus high concentration of anions enhanced COD removal in UV/O 3 but affected that in CuO@Al 2 O 3 /O 3. The study further revealed the characteristics of heterogeneous catalytic O 3 and UV/O 3 , and UV induced excited state should be considered in UV-based advanced oxidation processes (AOPs). [Display omitted] • UV/O 3 was more efficient than CuO@Al 2 O 3 /O 3 for MSW incineration leachate treatment. • CuO@Al 2 O 3 /O 3 had stronger mineralization effect but suffered the problem of self-quenching. • UV induced excited state explained the absence of self-quenching in UV/O 3. • O 3 , ≡Cu–O·, ·OH had different selectivity, and UV/O 3 exhibited a unique three-stage mechanism. • High salinity enhanced the mineralization ability of UV/O 3 due to the presence of UV induced excited state. [ABSTRACT FROM AUTHOR]

• The electronic structures of SnBr are calculated with MRCI+Q method. • The spin-orbit coupling effect is considered. • The predissociation mechanism of 14Σ- is discussed. • The avoided crossing phenomenon of the same symmetry is analyzed. • The lifetimes of vibrational states of 12Σ+ are evaluated. The electronic structures and spectroscopic properties of SnBr molecule are calculated by high-level multireference configuration interaction (MRCI) method. The Davidson correction (+Q) and spin-orbit coupling (SOC) effect are investigated in the calculations. The potential energy curves (PECs) of 23 Ʌ-S states and 45 Ω states generated from those Ʌ-S states are obtained. Based on the calculated PECs, the spectroscopic constants of the bound states are evaluated, which are in good accordance with previous experimental data. At the avoided crossing point, the dipole moments (DMs) of Ʌ-S states exhibit abrupt change, which are attributed to the change of electronic configurations of those states. With the help of the calculated SO matrix elements, the interaction between 14Σ- and nearby states is analyzed, and the possible predissociation pathway of low-lying vibrational levels of 14Σ- is illuminated. In the end, transition dipole moments (TDMs) and the radiative lifetimes from the excited states to the ground state are determined. [Display omitted] The calculated potential energy curves of the Λ-S states of SnBr using MRCI+Q method. [ABSTRACT FROM AUTHOR]

[Display omitted] • Sensing mechanism of a fluorescence probe for fluoride and sulfite is theoretically confirmed. • Calculated VTEs are in good agreements with the UV–Vis and fluorescent spectra. • The probe-fluoride reaction product undergoes an ESPT process through hydrogen bonding. • ESPT process results in a red-shifted fluorescence of the probe. • Fluorescence of the probe is blue-shifted due to the inhibition of ICT process by sulfite. TDDFT method was applied to study the excited-state mechanism of a reported fluorescent probe for fluoride and sulfite. Theoretical results showed the excitation of the probe molecule involved an intramolecular charge transfer process. Based on potential energy scanning and frontier orbital analysis, the excited-state proton-transfer process of the fluoride-probe product resulted in the significant red-shifted fluorescence. In contrast, the intramolecular charge transfer process was inhibited by sulfite anions. Due to the curtailing of the conjugated system, a blue-shifted emission was observed in the fluorescence spectrum. By exploiting the difference in fluorescence wavelengths, fluoride and sulfite anions could be recognized. [ABSTRACT FROM AUTHOR]

[Display omitted] • The effect of exchange–correlation functionals on charge-transfer excited states is tested. • The explicit solvent model gives a reasonable description of the electronic structure based on the QM/MM approach. • Red-shifts of the emission peak with increasing solvent polarity was reproduced in the theoretical calculations. ABSTRAC:A typical thermally activated delayed fluorescence (TADF) molecule, 3DPyM-pDTC was investigated theoretically in terms of geometric structure, absorption and emission spectra, and luminescence rates. The result of different XC functionals, the implicit and explicit solvent models on calculating geometries, and electron structures of the excited states were compared comprehensively. It's found that time-dependent density functional theory (TDDFT) with the PBE0 functional could give a rational description of the electron structure of 3DPyM-pDTC employing the explicit solvent model based on QM/MM. Red-shifts of the emission peak with increasing solvent polarity was reproduced. The TADF properties in the solid phase reproduced well. [ABSTRACT FROM AUTHOR]

The effect of electrochemical degradation on Magnéli phase Ti 4 O 7 anode combined with UV irradiation on the removal of PFOS was systematically evaluated in the present study. A synergistic effect of electrolysis and UV irradiation rather than a simple additive effect for PFOS degradation was demonstrated experimentally and theoretically. The short wavelength irradiation within 400 nm is the main contribution to enhance the electrochemical degradation of PFOS, while the initial pH of the solution has little effect on the PFOS degradation. The increase of current density accelerates the removal of PFOS either by electrolysis treatment or the joint process. The time-dependent density functional theory (TD-DFT) calculation indicates that the synergistic effect of the electrolysis and UV irradiation is most likely due to the involvement of the excited PFOS induced under UV irradiation in the electrochemical reaction. This study provides the first mechanistic explanation for the electrochemical degradation of PFOS enhanced by UV irradiation. [Display omitted] • PFOS degradation by electrolysis on Ti 4 O 7 anode combined with UV irradiation was studied. • A synergistic effect exists between electrolysis and UV irradiation for PFOS degradation. • TD-DFT calculation elucidates the synergistic mechanism of electrolysis and UV irradiation. • Excited PFOS induced by UV reduces the anodic potential required for electrolysis. [ABSTRACT FROM AUTHOR]

To tune the efficiency of organic semiconductor devices it is important to understand limiting factors as trapping mechanisms for excitons or charges. An understanding of such mechanisms deserves an accurate description of the involved electronical states in the given environment. In this study, we investigate how a polarizable surrounding influences the relative positions of electronically excited states of dimers of different perylene dyes. Polarization effects are particularly interesting for these systems, because gas phase computations predict that the CT states lie slightly above the corresponding Frenkel states. A polarizable environment may change this energy order because CT states are thought to be more sensitive to a polarizable surrounding than Frenkel states. A first insight we got via a TD-HF approach in combination with a polarizable continuum model (PCM). These give limited insights because TD-HF overestimates excitation energies of CT states. However, SCS-CC2 approaches, which are sufficiently accurate, cannot easily be used in combination with continuum solvent models. Hence, we developed two approaches to combine gas phase SCS-CC2 results with solvent effects based on TD-HF computations. Their accuracies were finally checked via ADC(2)//COSMO computations. The results show that for perylene dyes a polarizable surrounding alone does not influence the energetic ordering of CT and Frenkel states. Variations in the energy order of the states only result from nuclear relaxation effects after the excitation process. © 2016 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

In this work, the low-lying electronic singlet states of 9-methylhypoxanthine (9MHPX) were explored by the complete active space self-consistent-field (CASSCF) and complete active space second-order perturbation theory (CASPT2) calculations, and the conical intersections between the optically bright excited S1state and ground S0state were optimised by the two-root state-averaged SA-2-CASSCF approach. These studies indicate that four slightly different kinds of S1/S0conical intersections are identified computationally for 9MHPX, corresponding to four main internal conversion pathways, respectively, all of which are found to show the comparable timescales according to dynamics simulations. At the CASPT2 level, four brightππ* transitions of 9MHPX are calculated to locate at 4.47, 5.35, 5.97 and 6.30 eV, respectively, responsible for the available experimental absorption peaks of 9MHPX in the vapour phase (4.41, 5.19, 6.05 and 6.42 eV). Though one relatively weakππ* transition computed at 5.69 eV is not observed in the vapour phase, it is in accordance with the circular dichroism measurement of another hypoxanthine derivative deoxyinosine 5'-phosphate near 5.51 eV. [ABSTRACT FROM AUTHOR]

We have performed a series of calculations using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) for 1-methylamideanthraquinone (MAAQ). In the S0 state of MAAQ, amide group is coplanar with anthraquinone, and an intramolecular hydrogen bond is formed. The transition has an intramolecular charge transfer character. Two stable structures (planar nMAAQ and twisted tMAAQ) have been obtained in the S1 state of MAAQ. Thereinto, nMAAQ is lower by 0.105eV than tMAAQ in energy, so nMAAQ is the dominant conformation in the S1 state of MAAQ and the emission spectra of tMAAQ cannot be observed in the solution of MAAQ. Excited state intramolecular proton transfer (ESIPT) between CO and N-H was not observed in the S1 state of MAAQ. Upon addition of fluoride anion, only twisted conformations were obtained in both S0 and S1 states of MAAQ-F. An intermolecular hydrogen bond is formed in the S0 state, and intermolecular proton transfer happens in the S1 state for MAAQ-F. • We find a stable conformer with an intramolecular C=O⋯H-N hydrogen bond for the S0 state of 1-methylamideanthraquinone (MAAQ). • There are two stable conformers (planar nMAAQ and twisted tMAAQ) in the S1 state of MAAQ, corresponding to two emission peaks in fluorescence spectra. • Upon addition of fluoride anion, doprotonation can occur in both S0 and S1 states of MAAQ. [ABSTRACT FROM AUTHOR]

A variety of AB2 type new target dyes containing two proton transfer segments ( o -hydroxy-phenyl-imino) are presented in this study. Furthermore, the corresponding reference molecules absent of hydroxy or imino groups are provided as well. Dual intramolecular hydrogen bonds in the target dyes are demonstrated by 1 H NMR spectra, X-ray single crystal analysis as well as one-photon absorption spectra. Linear emission properties (static and transient emission nature) and two-photon absorption optical properties of these target and reference dyes are determined in various media such as organic solvents, solid phase state as well as PMMA substrate. The results show that the new AB2 type target dyes can efficiently undergo internal proton transfer in the excited states under one-photon irradiation and near-infrared femtosecond laser two-photon irradiation, respectively, and thus they exhibit well-separated dual-emission. The molecular geometry optimization is performed for the analysis of the occurrence of internal proton transfer in the excited states of the target AB2 chromophores. [ABSTRACT FROM AUTHOR]

So far, coumarin dyes have been extensively studied with various means to understand their photophysical behaviors and properties. Here, our performing time-dependent density functional theory calculation is aimed at exploring the excited-state hydrogen bonding dynamics of coumarin 153 (C153) in protic ethanol (EtOH) solvent. The calculated results suggest that the excited-state hydrogen bond CO⋯HO between CO group and OH group in the C153-EtOH complex is strengthened, and the S0 → S1 transition of the complex corresponds to the highest occupied molecular orbital (HOMO) hopping to the lowest unoccupied molecular orbital (LUMO). The excited-state hydrogen bond strengthening has been further confirmed by its larger binding energy in the S1 state than in the S0 state. In addition, because of the formation of the hydrogen bond CO⋯HO, a red shift of about 7 nm occurs in the electronic spectra of the C153-EtOH complex, which is in good accordance with the experiment result. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

N-Hydroxypyridine-2(1H)-thione (N-HPT) is an important photochemical generator of hydroxyl radicals; however, it has been pointed out that N-HPT is not a specific precursor of hydroxyl radical. Photoionization of N-HPT competes with photochemical N–O bond cleavage in neutral aqueous solution. The possibility of a competitive reaction could be critical for studies using N-HPT as the radical precursor; therefore, the detailed behaviors of electronic excitation and ionization of N-HPT and its deprotonated anion, which is the dominant tautomer under neutral pH conditions, are studied using quantum chemical methods with the symmetry-adapted cluster-configuration interaction (SAC-CI) method and the polarizable continuum model (PCM). The detailed assignment of the UV–Vis spectra of N-HPT is provided, and the origin of the observed negative solvatochromism is found to be the charge transfer excitation between the sulfur and the pyridine ring. The photochemical N–O bond cleavage occurs via the conical intersections between the lowest π → π* and π → σ* states and between the π → σ* and ground state, when N-HPT dissociates into PyS· and ·OH radicals. The calculated ionization potentials of N-HPT and the deprotonated N-HPT anion are 5.75 and 4.67 eV in PCM water. This demonstrates that the charge transfer excitation energy between N-HPT and liquid water becomes significantly lower for the deprotonated anion in comparison with the neutral molecule. Even under mild photochemical conditions, photoinduced ionization of N-HPT may occur in neutral aqueous solution. [ABSTRACT FROM AUTHOR]

Numerical computations of ground and excited states of Bose–Einstein condensates (BECs) require high spatial resolution due to the presence of the multiscale structures and boundary layers and interior layers in the solution. In this paper, a new discontinuous Galerkin (DG) method is presented for the computation of ground and excited states of BECs. For the spatial discretization, the direct discontinuous Galerkin (DDG) method is applied by using the normalized gradient flow. For the time discretization, we integrate the ordinary differential equations (ODEs) which is obtained by linearizing the interaction term. To evaluate the matrix exponential operator efficiently, we apply the Krylov subspace approximations to the matrix exponential operator. Numerical examples with different potentials are reported to demonstrate the validity and effectiveness of the semi-implicit DG method. [ABSTRACT FROM AUTHOR]

Theoretical chemistry provides a panel of powerful tools to investigate the geometries and electronic properties of excited states. However, it is necessary to benchmark the accuracy of existing models to determine the range of their applicability and accountability. In the present work, the performance of two related methodologies in this context, symmetry-adapted cluster-configuration interaction (SAC-CI) and time-dependent double-hybrid density functional theory (TD-DHDFT), is compared in detail for the calculation of absorption and fluorescence energies of small organic molecules and π-conjugated heteroaromatic compounds. Pragmatically, for the SAC-CI calculations the singles and doubles linked excitation operators are considered in the wave functions. On the other hand, for the TD-DHDFT calculations the linear-response Tamm–Dancoff formalism has been imposed. The considered DH density functionals include the approximations from both families of adjusted and non-adjusted models. Our numerical data reveal that of the tested adjusted DHs, B2-PLYP performs the best, while among the category of non-adjusted approximations the PBE0-DH functional outperforms others. Furthermore, the DH density functionals show deviations less than those obtained from SAC-CI method. Putting all the results together, the B2-PLYP and B2GP-PLYP functionals are found to be superior for overall performance. Altogether, the present contribution and recent efforts in this arena point out that besides the ground-state properties the DH approximations have also unquestionably entered into the field of excited-state calculations, where the DHDFT again comes into play and further evidence on the quality of the corresponding models is pronounced. [ABSTRACT FROM AUTHOR]

The time-dependent density functional theory (TDDFT) method has been carried out to investigate the hydrogen bonding dynamics of a series of hydrogen-bonded complexes of PYP chromophore formed with water molecules both in vacuum and aqueous solution. We demonstrate that the intermolecular hydrogen bonds formed between carbonyl oxygen and hydrogen of water are strengthened in the lowest bright state as well as one other charge transfer state and result in spectral redshift. Whereas, a totally opposite result happens to the site of phenolate oxygen, which can be confirmed based on the excited-state geometric optimizations by TDDFT method. In addition, the frontier molecular orbital analysis reveals the nature of the lowest bright state and the CT state as well as the understanding of the electronic excited-state hydrogen bonding dynamics. Moreover, two approaches are adopted to consider the solvation effect. [ABSTRACT FROM AUTHOR]

We present an efficient real-time time-dependent density functional theory (TDDFT) method for large-scale accurate simulations of electron–nucleus dynamics, as implemented in the time dependent ab-initio package (TDAP). By employing a local basis-set presentation, we are able to simulate systems of large size (∼500 atoms) and for long electronic propagation time (∼300–500 fs) with less computation cost while maintaining relatively high accuracy. We show several quintessential examples, such as photoabsorption spectra of dye-sensitized TiO 2 nanowire, proton transfer coupled nonradiative relaxation of eumelanin constituents, electron injection and electron–hole recombination in dye solar cells, hole-transfer dynamics between MoS 2 /WS 2 interlayer heterojunction, and solvent effects on electron dynamics. Our method is demonstrated to have superiority over available methods in dealing with interesting excited state characteristics of complex systems involving dynamics of electrons and atoms. [ABSTRACT FROM AUTHOR]

A search for double-beta decays of 136 Xe to excited states of 136 Ba has been performed with the first phase data set of the KamLAND-Zen experiment. The 0 1 + , 2 1 + and 2 2 + transitions of 0 ν β β decay were evaluated in an exposure of 89.5 kg ⋅ yr of 136 Xe, while the same transitions of 2 ν β β decay were evaluated in an exposure of 61.8 kg ⋅ yr . No excess over background was found for all decay modes. The lower half-life limits of the 2 1 + state transitions of 0 ν β β and 2 ν β β decay were improved to T 1 / 2 0 ν ( 0 + → 2 1 + ) > 2.6 × 10 25 yr and T 1 / 2 2 ν ( 0 + → 2 1 + ) > 4.6 × 10 23 yr (90% C.L.), respectively. We report on the first experimental lower half-life limits for the transitions to the 0 1 + state of 136 Xe for 0 ν β β and 2 ν β β decay. They are T 1 / 2 0 ν ( 0 + → 0 1 + ) > 2.4 × 10 25 yr and T 1 / 2 2 ν ( 0 + → 0 1 + ) > 8.3 × 10 23 yr (90% C.L.). The transitions to the 2 2 + states are also evaluated for the first time to be T 1 / 2 0 ν ( 0 + → 2 2 + ) > 2.6 × 10 25 yr and T 1 / 2 2 ν ( 0 + → 2 2 + ) > 9.0 × 10 23 yr (90% C.L.). These results are compared to recent theoretical predictions. [ABSTRACT FROM AUTHOR]

Symmetrical and unsymmetrical 4,4′-biphenyl, and 9,10-anthracene derivatives with tris(trifluoromethyl)germylethynyl –C C–Ge(CF 3 ) 3 substitutes have been prepared, their properties have been studied and compared with those of dimethyl(phenyl)silylethynyl –C C–Si(Ph)Me 2 compounds. UV–visible absorption, steady-state, and time-resolved fluorescence spectra in solution for this germanium and silicon compounds have been investigated. The process of photoinduced electron-transfer from the aromatic group to the germanium center has been found in the unsymmetrical 4-biphenyl –C C–Ge(CF 3 ) 3 molecule. Anthracene derivatives with –C C–Ge(CF 3 ) 3 substitutes have been characterized crystallographically. [ABSTRACT FROM AUTHOR]

Dye sensitizers can significantly affect power conversion efficiency of dye-sensitized solar cells (DSSCs). Porphyrin-based dyes are promising sensitizers due to their performances in DSSCs. Here, based upon a N-fused carbazole-zinc porphyrin-free-base porphyrin triad containing an ethynyl-linkage (coded as DTBC), the novel porphyrin dyes named DTBC-MP and DTBC-TP were designed by varying the porphyrin-free-base units in the π conjugation of DTBC in order to study the effect of porphyrin-free-base in the modification of electronic structures and related properties. The calculated results indicate that, the extension of the conjugate bridge with the porphyrin-free-base unit results in elevation of the highest occupied molecular orbital (HOMO) energies, decrease of the lowest unoccupied molecular orbital (LUMO) energies, reduction of the HOMO-LUMO gap, red-shift of the absorption bands, and enhancement of the absorbance. The free energy changes demonstrate that introducing more porphyrin-free-base units in the conjugate bridge induces a faster rate of electron injection. The transition properties and molecular orbital characters suggest that the different transition properties might lead to a different electron injection mechanism. In terms of electronic structure, absorption spectra, light harvesting capability, and free energy changes, the designed DTBC-TP is a promising candidate dye sensitizer for DSSCs. [ABSTRACT FROM AUTHOR]

Dicyanophenyl derivatives, DCN1 – 3 , were rationally synthesized and their thermally activated delayed fluorescence properties were investigated. OLED devices were further fabricated using DCN1 – 3 . Particularly DCN3 (5-{3,6-di(9 H -carbazole-9-yl)-9 H- carbazol-9-yl}isophthalonitrile) showed excellent device performances employing TADF mechanism with power efficiency of 15.26Cd/A, luminous efficiency of 8.14 lm/W, the maximum external quantum efficiency of 13.33%, and brightness of 1526 Cd/m 2 . [ABSTRACT FROM AUTHOR]

A comparison of excited state and electroluminescent properties between Pt(C^N^N)Cl and Pt(N^C^N)Cl complexes has been done with Time-Dependent Density Functional Theory (TDDFT), [C^N^N = 6-phenyl-2,2-bipyridine, N^C^N = 1,3-di(2-pyridyl)benzene]. The substituent effect of fluorine ligands on eight tridentate cyclometalated Pt(C^N^N)Cl complexes has been investigated, which includes electronic density variation between ground states and excited states, absorption and emission spectra, quantum yields and radiative lifetime. In addition, one dimeric form of Pt(C^N^N)Cl complex has been investigated. [ABSTRACT FROM AUTHOR]

Efficient exciplex organic light-emitting diodes (OLEDs) have been fabricated with an intermixed light-emitting layer comprising electron-rich m-MTDATA or TAPC as a donor and bipolar material 26DCzPPy as an acceptor. Intermolecular charge–transfer interaction between various donor materials with different highest occupied molecular orbital (HOMO) levels and 26DCzPPy are systematically investigated to explore the formation principle of the exciplex. Various techniques like steady state absorption and photoluminescence (PL) spectra, temperature dependent transient PL decay and time-resolved emission spectra (TRES) using time-correlated single-photon counting (TCSPC) principle were adopted to probe the electronic and optical properties of these exciplex systems. Strong exciplex emission was found from the m-MTDATA:26DCzPPy and TAPC:26DCzPPy mixed systems. The devices comprising these two exciplex systems as the emission layer exhibited a promising external quantum efficiency and a high exciton utilization efficiency due to the triplet exciton up-conversion from triplet to singlet states inspired by their small singlet–triplet exchange energy. Our current work contributes to know more about the unique intermolecular charge–transfer property between electron-rich donors and bipolar acceptors, and provides valuable exploration on developing novel high-performance exciplex OLEDs. [ABSTRACT FROM AUTHOR]

A new ruthenium complex, [Ru(bpy) 2 (dbe-ppl)](PF 6 ) 2 (bpy = 2,2′-bipyridine and dbe-ppl = dimethyl 4,4′-(pyrazino[2,3-f][1,10]phenanthroline-2,3-diyl)dibenzoate, has been synthesized and characterized by 1 H NMR spectroscopy, UV–Vis, IR, and cyclic voltammetry. Irradiation on the MLCT band results in photoluminescence in both protic and aprotic solvents. The photoluminescence in water is pH dependent, it shows a behavior which can be described by the Henderson–Hasselbalch assuming the protonation/deprotonation of the excited state with a pKa of 2.40 ± 0.01. [ABSTRACT FROM AUTHOR]

6-Aminophenanthridine (6AP) and its derivatives show important biological activities as antiprion compounds and inhibitors of the protein folding activity of the ribosome. Both of these activities depend on the RNA binding property of these compounds, which has been recently characterized by fluorescence spectroscopy. Hence, fundamental insights into the photophysical properties of 6AP compounds are highly important to understand their biological activities. In this work, we have calculated electronic structures and optical properties of 6AP and its three derivatives 6AP8CF3, 6AP8Cl, and 6APi by density functional theory (DFT) and time-dependent density functional theory (TDDFT). Our calculated spectra show a good agreement with the experimental absorption and fluorescence spectra, and thus, provide deep insights into the optical properties of the compounds. Furthermore, comparing the results obtained with four different hybrid functionals, we demonstrate that the accuracy of the functionals varies in the order B3LYP > PBE0 > M062X > M06HF. © 2015 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Six recently synthesized arylamine-imidazole combo dyes, utilized in dye-sensitized solar cells staining TiO 2 semiconductor, were spectroscopically investigated. Studies were performed with application of steady-state and time-resolved absorption spectroscopies and were done on dyes dissolved in dichloromethane and anchored on TiO 2 /FTO film support. The investigations allowed to characterize the excited state decay dynamics of individual compounds, determine time constants of dye-to-TiO 2 electron injection process for dyes adsorbed on TiO 2 /FTO support and subsequent recombination and dye regeneration dynamics. These studies were performed on bare dye/TiO 2 /FTO photoanodes in air environment and, if possible, on the same samples with dye layer immersed in electrolyte solution. These evaluations allowed to determine approximate time constants for dye regeneration and directed toward dye that reveals most advantageous properties and hypothetically should outperform its counterparts as TiO 2 sensitizer. [Display omitted] • Excited state lifetimes of six arylamine-imidazole dyes were measured in solvent. • fs and ns transient absorption of FTO/TiO 2 dyes films performed. • Evaluation of dynamics electron injection to TiO 2 assessed with global analysis. • Dynamics of intrinsic dye+-(TiO 2)- recombination spectroscopically evaluated. [ABSTRACT FROM AUTHOR]

At present, the safety and environmental compatibility of commercial sunscreens are becoming unprotected. Most of the commercial sunscreens lack absorption and protection in high-energy UVA area. In this work, it has been proved that biflavonoids have sunscreen properties for the first time, especially, Amentoflavone (AME) covers almost the entire UV region and has high absorption. Different substituents have a great influence on the UV absorption of bisflavonoids. Therefore, we can adjust the substituents to obtain a broad protection region for sunscreens. Depending on the two-proton transfer donor and acceptor sites, it is theoretically proved that there is a reasonable competitive relationship between the two structures, and only one part of the proton transfer can be carried out in the molecule, which proved to be the proton donation of H 1 –O 1 –H 2. When UV excited, biflavonoids will form intramolecular hydrogen bonds through proton transfer and emit energy in an ultra-fast pathway. Biflavonoid precursors could be used in sunscreen field and then the mechanism was proved, and it is a breakthrough in the research of expanding the field of plant filter. AME performs better than the current mature commercial sunscreens, and this work provided theoretical support to design a new biflavonoids for UV protection in future. [Display omitted] • Plant-derived flavonoids Amentoflavone and Isoginkgentin have potential UVA and UVB sun protection properties. • Intramolecular proton transfer (ESIPT) takes place in the excited state for both compounds. • The broad-spectrum sunscreens could be realized by adjusting the position and number of substituents. [ABSTRACT FROM AUTHOR]

Employing exciplex to capture the triplet excitons has been proved to be an effective strategy in organic light-emitting diodes (OLEDs). However, the detailed exciton formation pathways in exciplex-based OLEDs are still ambiguous. Here, the spin-dependent exciton formation in exciplex-based OLEDs is visualized by magnetic field effect technique. The results show that when excitons are formed on donor 2,6-bis(3-(9H-carbazol-9-yl)phenyl)pyridine (26DCzPPy) molecules, the magnetic field effect on electroluminescence (MEL) exhibits a hyperfine style line-shape with narrow half-peak width. In contrast, when excitons are directly formed on the donor-acceptor (D-A) interface in the bulk heterojunction, the MEL exhibits a Δ g style line-shape with broad half-peak width. The line-shape of MEL could be an indicator of exciton formation mechanism. Our findings bring a new method to monitor the exciton formation pathways, which offer an opportunity for linking the exciton formation to device efficiency. [Display omitted] • Exciton formation and evolution have a great impact on the device performance. • MEL profiles could be an indicator of excion formation pathways. • The dominant Δg style indicates that excitons are directly formed across the D-A interface in the exciplex-based devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • Lock/unlock strategy proposed to manipulate excited states and photophysical properties of TADF materials. • Efficient TADF emitters with high PLQYs (up to 0.91), short TADF lifetimes and excellent stability and film-quality. • High-performance OLED with EQE beyond 25%. Thermally activated delayed fluorescent (TADF) materials have drawn widespread attentions due to their great potential for practical applications in organic light-emitting diodes (OLEDs). Deep understanding of the structure-excited state-photophysical property relationships is a key to rationally design TADF emitters. Herein, two new TADF molecules, TBP-DPXZ and TBQ-DPXZ, which consist of locked (triptycene-fused dibenzophenazine) and unlocked (triptycene-fused 2, 3-diphenylquinoxaline) electron-acceptors respectively and phenoxazine electron donors are reported. The comparative study reveals that the lock/unlock strategy could substantially manipulate the lowest locally excited (LE) and charge transfer (CT) states of these emitters via changing the acceptor strength, structural rigidity, and conjugation length, and in turn lead to significantly different photoluminescence (PL) and electroluminescence (EL) performance. It is notable that the unlocked molecule TBQ-DPXZ emits efficient green fluorescence with photoluminescence quantum yield of 91% and TADF lifetime of 3.6 μs in doped film. The doped OLED based on TBQ-DPXZ achieves an external quantum efficiency (EQE) of 25.1%, a current efficiency (CE) of 79.7 cd/ A, a power efficiency (PE) of 80.0 lm/W, and a maximum luminance of 18400 cd/m2, which are better than those of the TBP-DPXZ-based device and are among the best results reported so far for green TADF-OLEDs. [ABSTRACT FROM AUTHOR]

[Display omitted] • The fluoride-sensing mechanism of a fluorescent sensor is theoretically confirmed. • Calculated VTEs are in good agreements with experimental spectra. • Fluoride-sensor complex undergoes an ESPT process with a relatively high potential barrier. • ESPT alleviates the steric hindrance in the sensor and enlarges the conjugated system. • ESPT process leads to the red-shifted fluorescence upon the addition of fluoride. An understanding of the excited-state process and the sensing mechanism for specific anions can be helpful for the design and synthesis of fluorescent sensors in analytical chemistry and biotechnology. Here, we theoretically investigated the fluorescent response mechanism of a reported acylhydrazone-based fluorescent sensor (Soft Matter , 2019, 15, 6690) for fluoride recognition using the time-dependent density functional theory approach. At the M06/TZVP/SCM level, the vertical excitation energies, which were calculated based on the ground state and first singlet-state geometries of the sensor molecule, agreed well with the experimental ultraviolet–visible and fluorescence spectra. Therefore, the time-dependent density functional theory method was considered reasonable and effective. According to the frontier orbital analysis and an excited-state potential energy scan, we proposed an excited-state proton transfer mechanism for the sensor-fluorine complex, where the steric hindrance leads to a high potential barrier. The excited-state proton transfer process facilitates sensor molecule deprotonation, alleviates its steric hindrance effect and expands its conjugated system. As a result, the fluorescence emission band of the sensor molecule was red-shifted significantly with the addition of fluoride anion. Based on this fluorescence difference, the sensor could be used for fluoride anion identification. This work provides a strategy to study sensor–analyte interactions in the excited state and offers an approach to tune the fluorescence emission wavelength of sensor molecules in anionic environments. [ABSTRACT FROM AUTHOR]

The first search ever for the α-decay of 146Nd into the first excited state of 142Ce has been performed by using an ultra-low background High Purity Germanium (HPGe) detector and a Nd-sample with 97.20(1)% abundance of 146Nd. No significant signal could be observed with a measuring time of 144 h. A lower limit on the half-life of this decay mode has been determined to be T1/2 > 1.6 × 1018 years at 90% CL. [ABSTRACT FROM AUTHOR]

The influence of H-bond geometry on the dynamics of excited state intramolecular proton transfer (ESIPT) and photoinduced tautomerization in a series of phenol-quinoline compounds is investigated. Control over the proton donor-acceptor distance ( dDA) and dihedral angle between the proton donor-acceptor subunits is achieved by introducing methylene backbone straps of increasing lengths to link the phenol and quinoline. We demonstrate that a long dDA correlates with a higher barrier for ESIPT, while a large dihedral angle opens highly efficient deactivation channels after ESIPT, preventing the formation of the fully relaxed tautomer photoproduct. [ABSTRACT FROM AUTHOR]

Abstract Predicting FRET pathways in proteins using computer simulation techniques is very important for reliable interpretation of experimental data. A novel and relatively simple methodology has been developed and applied to purine nucleoside phosphorylase (PNP) complexed with a fluorescent ligand — formycin A (FA). FRET occurs between an excited Tyr residue (D*) and FA (A). This study aims to interpret experimental data that, among others, suggests the absence of FRET for the PNPF159A mutant in complex with FA, based on novel theoretical methodology. MD simulations for the protein molecule containing D*, and complexed with A, are carried out. Interactions of D* with its molecular environment are accounted by including changes of the ESP charges in S1, compared to S0, and computed at the SCF-CI level. FRET probability WF depends on the inverse six-power of the D*-A distance, Rda. The orientational factor 0

Three N-heteroleptic Pt(II) complexes, [Pt(C^C)(O^O)] [O^O = acetylacetonate, C^C = 1-phenyl-1,2,4-triazol-5-ylidene (1), C^C = 4-phenyl-1,2,4-triazol-5-ylidene (2), C^C = 2-phenylpyrazine (3)] have been investigated with density functional theory (DFT) and time-dependent density functional theory (TDDFT). The radiative decay rate constants of complexes 1–3 have been discussed with the oscillator strength ( f n ), the strength of spin–orbit coupling (SOC) interaction between the lowest energy triplet excited state (T 1 ) and singlet excited states (S n ), and the energy gaps between E (T 1 ) and E (S n ). To illustrate the nonradiative decay processes, the transition states between triplet metal-centered ( 3 MC) and T 1 states have been optimized and were verified with the calculations of vibrational frequencies and intrinsic reaction coordinate (IRC). In addition, the minimum energy crossing points (MECPs) between 3 MC and ground states (S 0 ) were optimized. At last, the potential energy curves relevant to the nonradiative decay pathways are simulated. The results show that complex 3 has the biggest photoluminescence quantum yield because the complex 3 has the biggest radiative decay rate constant and the smallest nonradiative decay rate constant in complexes 1–3. [ABSTRACT FROM AUTHOR]

To understand the reaction mechanism involving hydrogen transfers through hydrogen-bond bridge, we carried out both Self-Consistent Charge Density Functional Tight-Binding (SCC-DFTB) calculations of bulk nitromethane and Density Functional Theory (DFT) calculations of singlet ground state/triplet excited state molecular nitromethane using B3LYP functional. Firstly, we tuned the repulsive parameters of the SCC-DFTB method for nitromethane with dataset calculated from DFT at B3LYP/6-311g level. The molecular dynamics simulations are carried out with tuned parameters to get the dynamical properties of the bulk nitromethane, and the static calculations are intended to give energy profile of the reaction process. These calculations indicate the excitation of nitromethane molecule making the proton transfer reactions possible, and lowering the reaction barrier. Proton transfer reactions in high pressure condensed phase are discussed by means of semi-empirical tight-binding and time-dependent density functional theory (TD-DFT). The energy as a function of reaction path between ground and excitation state NM is computed. These results indicate the excitation of nitromethane molecule making the proton transfer easy to happen. [ABSTRACT FROM AUTHOR]

Using vis absorption, fluorescence spectral experimental data, and time-resolved measurement, we have examined the kinetics of Zinc(II)-2,9,16,23-phthalocyanine tetracarboxylate (()4), which is interesting photosensitizer of far red-absorption in water: solution. The kinetic parameters were measured and/or calculated. The photophysical properties originate principally from the planar macrocycle while the outer substituent and degree of carboxylation seem not to have a considerable influence on the kinetic parameters. The nonradiative rate constants of the first excited state were dominant due to the heavy metal effect. Using the obtained photophysical parameters, the population dynamics were calculated by kinetic model. On nanosecond scale of 15 ns, about 63% population of the first excited-singlet state is retrieved by the ground state. Whereas, the rest of population are deactivated to the first excited-triplet state. Later on, during about 7 μs starting from the initial decay of the first excited singlet state, the first excited singlet state and the first excited triplet state were completely empty, meanwhile the ground state retrieved its initial population. Due to the fact that ()4 has strong absorption, long lifetimes of the first singlet and triplet excited states, and fast intersystem crossing, it may be suitable for nonlinear optical studies. [ABSTRACT FROM AUTHOR]

In this work, the excited state intermolecular potential energy surface of the Ar–CS2(V1B2) van der Waals complex was evaluated for the first time. The calculation of more than 4000 single-point interaction energies for the complex using an equation-of-motion coupled-cluster model with single and double substitutions level of theory with extended basis set involving bond functions has been performed. After fitting the interaction energies to analytical functions, the emission spectra of the Ar–CS2(V1B2) complex related to the different stationary points on the potential energy surface were calculated. It was seen that the intensity and the position of the emission spectra are dependent on the orientation of the Ar atom around the bent excited CS2and the distance between two components. The information about the structural parameters of the complex related to the global minimum was obtained under the pseudodiatomic approximation with assistance ofab initiopotential. The presented investigation could be useful for further theoretical and experimental studies of Ar–CS2(V1B2) complex. [ABSTRACT FROM AUTHOR]

A two new compounds with potential biologically active were synthesized: ethyl 4-(2H-4,6-dimethyl-3-oxo-2,3-dihydroisothiazolo [5,4-b] pyridin-2-yl) butanoate and ethyl 4-(2H-4,6-dimethyl-2,3-dihydroisothiazolo [5,4-b] pyridin-3-yloxy) butanoate. The structures of all of the newly formed compounds were identified by elemental analysis, FTIR and H NMR. Their optical properties were studied in ethanol and n-hexane by UV-Vis absorption and fluorescence spectroscopy. The ground-state and excited-state properties were investigated using the density functional theory (DFT) and the time-dependent density functional theory (TDDFT) methods. The results showed differences between emission spectra in ethanol and n-hexane solution (solvatochromism) for both new compounds. [ABSTRACT FROM AUTHOR]

A series of heteroleptic cyclometalated Ir (III) complexes for OLEDs application have been investigated theoretically to explore their electronic structures and spectroscopic properties. The geometries, electronic structures, and the lowest-lying singlet absorptions and triplet emissions of (piq) 2 Ir(acac) (labeled 1 ) and theoretically designed models (piq) 2 Ir(dpis) (labeled 2 ), (4Fpiq) 2 Ir(dpis) (labeled 3 ), (4F5M-piq) 2 Ir(dpis) (labeled 4 ), (4,5-2F-piq) 2 Ir(dpis) (labeled 5 ) and (5-F-piq) 2 Ir(dpis) (labeled 6 ) were investigated with density functional theory (DFT)-based approaches, where, piq = 1-phenylisoquinolato, acac = acetylacetonate and dpis = diphenylimidodisilicate. Their structures in the ground and excited states have been optimized at the DFT/B3LYP/LANL2DZ and TDDFT/B3LYP/LANL2DZ levels, and the lowest absorptions and emissions were evaluated at B3LYP and M062X level of theory, respectively. Furthermore, the energy-transfer mechanism of these complexes also be analyzed here, and the result shown that the complexes 1–6 are having the low efficiency roll-off property. Except that, the oscillator strength analyze shown that the complexes 2–6 , which were designed by theory, are suitable for OLED since their high oscillator strength property. [ABSTRACT FROM AUTHOR]

An explicit method for calculating the spatial distribution of excited species in the reaction cell is presented. This method is used to analyze the relation between experimental conditions (excitation wavelength, ground state concentration, and laser intensity) and the observed luminescence decays (and the corresponding reaction kinetics) in both transient emission and transient absorption pulse laser photolysis experiments. Subsequently, the analysis was applied to the experimental conditions of previously extensively studied pyrene excimer formation in cyclohexane (J.B. Birks, Photophysics of Aromatic Molecules, Wiley-Interscience, London, 1970) and significantly different data were obtained in the redesigned experiment; the excimer formation and decay rate constants at 23.5 °C were found to be (4.77±0.04)×10 9 M −1 s −1 and (2.07±0.01)×10 7 s −1 , respectively. Most importantly, the excimer dissociation into a singlet excited pyrene and ground state pyrene was found to be negligible, which is an important result that crucially affects the data processing in many previous and current applications of excimer formation. [ABSTRACT FROM AUTHOR]

New near-infrared two-photon absorption π-extended benzotriazole–coumarin dyads as target molecules were synthesized. The corresponding coumarin derivatives and esterified dyads were also prepared as the references. The experimental evidence of internal proton transfer in the excited state of the benzotriazole-based chromophores under one and near-infrared two-photon irradiation are firstly presented in this Letter. [ABSTRACT FROM AUTHOR]

The hydrogen bonded complexes of 6-aminocoumarin (6AC) with several water molecules in their ground and lowest excited singlet electronic state have been investigated using the ab initio methods. It was shown that the complex containing five water molecules in the surrounding of the amino group of the 6AC molecule has the lowest stabilization energy in the ground electronic state. This complex can serve as a model of the first solvation shell of the 6AC molecule in bulk water. The energies of hydrogen bonds formed by the carbonyl group with up to two water molecules were also determined. The calculated change in the total hydrogen bond energy due to S 0 →S 1 excitation is in good agreement with the experimental data [E. Krystkowiak, A. Maciejewski, Phys. Chem. Chem. Phys. 2011;13:11317–11324]. The maxima of absorption spectra of the hydrogen-bonded complexes, calculated taking into account nonspecific solute–solvent interactions, are in reasonable agreement with the experimental data. [ABSTRACT FROM AUTHOR]

The use of visible light to produce highly selective and potent drugs through photodynamic therapy (PDT) holds much potential in the treatment of cancer. PDT agents can be designed to follow an O 2 -dependent mechanism by producing highly reactive species such as 1 O 2 and/or an O 2 independent mechanism through processes such as excited state electron transfer, covalent binding to DNA or photoinduced drug delivery. Ru(II)-polypyridyl and Rh 2 (II,II) complexes represent an important class of compounds that can be tailored to exhibit desired photophysical properties and photochemical reactivity by judicious selection of the ligand set. Complexes with relatively long-lived excited states and planar, intercalating ligands localize on the DNA strand and photocleave DNA through 1 O 2 production or guanine oxidation by the excited state of the chromophore. Photoinduced ligand substitution occurs through the population of triplet metal centered ( 3 MC) excited states and facilitates covalent binding of the metal complex to DNA in a mode similar to cisplatin. Ligand photodissociation also provides a route to selective drug delivery. The ability to construct metal complexes with desired light absorbing and excited state properties by ligand variation enables the design of PDT agents that can potentially provide combination therapy from a single metal complex. [ABSTRACT FROM AUTHOR]