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Excited-state descriptors based on the one-particle transition density matrix referring to the exciton picture have been implemented for time-dependent density functional theory. State characters such as local, extended pp*, Rydberg, or charge transfer can be intuitively classified by simple comparison of these descriptors. Strong effects of the choice of the exchange-correlation kernel on the physical nature of excited states can be found and decomposed in detail leading to a new perspective on functional performance and the design of new functionals. [ABSTRACT FROM AUTHOR]

The electrostatic attraction between the separated charges in long-range excited charge-transfer states originates from the non-local Hartree-Fock exchange potential and is, thus, a non-local property. Present-day time-dependent density functional theory employing local exchange-correlation functionals does not capture this effect and therefore fails to describe charge-transfer excited states correctly. A hybrid method that is qualitatively correct is described. [ABSTRACT FROM AUTHOR]

The synthesis of a doubly bridged tolane is reported. The target is obtained in a five‐step synthesis, starting from commercially available 2‐amino‐meta‐xylene by a combination of a Sandmeyer reaction, radical bromination, and Stille‐type coupling, followed by double ring closing. The doubly tethered tolane is crystalline; the two phenyl rings are highly twisted with respect to each other both in solution and in the solid state. Optical spectroscopy and quantum chemical calculations show that the doubly bridged tolane is twisted not only in the ground state, but also in the excited state, leading to emission from the twisted state in solution and in the solid state. Strong phosphorescence is observed at cryogenic temperatures. Let's twist again: Two tethers fix the two phenyl rings of the target structure, a tolane, in a twisted fashion—even in the electronically excited state. The double bridging is necessary because a single linker is not sufficient to hold the two phenyl rings perpendicular to each other in the excited state. [ABSTRACT FROM AUTHOR]

The applicability and limitations of the restricted virtual space (RVS) approximation within the algebraic-diagrammatic construction (ADC) scheme for the polarization propagator up to third order is evaluated. In RVS-ADC, not only the core but also a substantial amount of energetically high-lying virtual orbitals is restricted in excitation energy calculations of low-lying excited electronic states. Using octatetraene, indole, and pyridine as representative examples and different standard basis sets of triple-zeta quality, RVS-ADC(2) turns out to be highly useful and to have negligible effects on ππ* excited states. However, for nπ* or πσ* states, the RVS approximation is generally less reliable but better at third-order than second-order ADC level. In addition, a unified, basis-set independent, thus normalized virtual orbital threshold (value) is introduced, making the RVS approximation more controllable and a priori applicable. © 2017 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The excited states of fac-tris(phenylpyridinato)iridium[Ir(ppy)3] and the smaller model complex Ir(C3H4N)3are computed using a number of high-levelab initio methods, including the recently implemented algebraic diagrammaticconstruction method to third-order ADC(3). A detailed descriptionof the states is provided through advanced analysis methods, whichallow a quantification of different charge transfer and orbital relaxationeffects and give extended insight into the many-body wave functions.Compared to the ADC(3) benchmark an unexpected striking differenceof ADC(2) is found for Ir(C3H4N)3, which derives from an overstabilization of charge transfer effects.Time-dependent density functional theory (TDDFT) using the B3LYP functionalshows an analogous but less severe error for charge transfer states,whereas the ωB97 results are in good agreement with ADC(3).Multireference configuration interaction computations, which are inreasonable agreement with ADC(3), reveal that static correlation doesnot play a significant role. In the case of the larger Ir(ppy)3complex, results at the TDDFT/B3LYP and TDDFT/ωB97levels of theory are presented. Strong discrepancies between the twofunctionals, which are found with respect to the energies, characters,as well as the density of the low lying states, are discussed in detailand compared to experiment. [ABSTRACT FROM AUTHOR]

Nitrodibenzofuran (NDBF) has recently been established as photolabile protecting group and efficiently used as two-photon active cage. In this work, a computational approach is exploited to rationally design improved two-photon active caging groups based on this NDBF chromophore. For this objective, first the two-photon absorption (TPA) properties of NDBF are investigated in detail and a suitable theoretical approach for the reliable simulation of TPA spectra of this class of compounds is identified. Then, virtual chemical modifications are performed by introduction of substituents at the chromophore and replacement of the central furan ring by pyrolle, thiophene, and borrole heterocycles. Subsequently, the TPA properties of the resulting compounds are computed, and the influences of the chemical modifications on TPA properties investigated in detail. The most promising candidates with largely increased two-photon uncaging efficiencies are dimethylamino-substituted derivatives of NDBF, nitrodibenzopyrrol, and nitrodibenzothiophene. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Using time-dependent density functional theory, the excited electronic states of the astaxanthin radical cation (AXT·+) are investigated. While the optically allowed excited D1 and D3 states are typical ππ∗ excited states, the D2 and D4 states are nπ∗ states. Special emphasis is put onto the influence of the carbonyl groups onto the excited states. For this objective, the excited states of four hypothetical carotenoids and zeaxanthin have been computed. Addition of a carbonyl group to a conjugated carbon double bond system does essentially not change the vertical excitation energies of the optically allowed nπ∗ states due to two counter-acting effects: the excitation energy should increase due to the –M-effect of the carbonyl group and at the same time decrease owing to the elongation of the conjugated double bond system by the carbonyl group itself. [Copyright &y& Elsevier]

The article presents a survey of single-reference ab initio excited state methods, which can be used for large molecules and to not explicitly include correlation through the ground-state wave function. Time-dependent density functional theory is currently the most popular technique for the computation of excited states of medium-sized and large molecules. With the advances in computer technology, systems up to 300 second-row atoms became possible.

With the concept of scaled-opposite-spin (SOS), a pragmatic semi-empirical approximation has been introduced to the extended algebraic diagrammatic construction scheme of second order (ADC(2)-x) that leads to a significant saving in computational effort. The parameters included were fitted with respect to a benchmark set of electronically excited states in standard organic molecules that include some doubly-excited states, as well. Like the original, unscaled ADC(2)-x scheme it can be used to identify electronically excited states with high double excitation character, however at reduced computational cost. At the same time, it is possible to reduce the overestimation of doubly-excited configurations that is inherent to ADC(2)-x. Additionally, a scheme for the strict variant (ADC(2)-s) was derived directly from SOS-MP2 by application of the intermediate state formalism and compared to an existing version of SOS-ADC(2)-s. [ABSTRACT FROM AUTHOR]

Examines the characterization of the relevant excited states in the photodissociation of carbon oxide-ligated hemoglobin and myoglobin. Structure of the myoglobin model complex; Potential energy curves of the lowest-excited singlet states of the complex.

The photodecarboxylation mechanismof different structural isomersof nitrophenylacetate (NPA) has been investigated using quantum chemicalcalculations as well as time-resolved UV-pump VIS-probe spectroscopy.It is shown that for a proper theoretical description of the excitedstates of anionic NPA in aqueous solution a careful considerationof the influence of the solvent is indispensable. In this sense, NPAis an example that demonstrates how character and lifetime of theinvolved excited states affect the results of equilibrium and nonequilibriumsolvation approaches. An ultrafast decay channel via a repulsive singletstate has been found to be responsible for observed ultrafast CO2release, while another very efficient but slower CO2release channel is found to proceed via intersystem crossing andsubsequent decay via a repulsive triplet state. After all, differencesand similarities in the observed excited state dynamics of the isomersare conclusively explained. Most notably, the much smaller quantumyield of CO2release from the ortho-isomer is due to analternative excited-state hydrogen-transfer channel, which occursalong a triplet and singlet pathway. On the basis of theoretical andexperimental evidence suggesting that the multiplicity of the routetaken determines the photoproduct yield, we provide guidelines forthe design of ortho-nitrobenzylic caging groups with improved uncagingyield. [ABSTRACT FROM AUTHOR]

Steady-state and time-resolved polarized spectroscopy studies reveal that electronic excitation to the third excited state of 1,4-distyryl-2,5-bis(arylethynyl)benzene cruciforms results in fluorescence emission that is shifted an angle of ca. 60°. This result is consistent with quantum chemical calculations of the lowest electronic excited states and their transition dipole moments. The shift originates from the disjointed nature of the occupied molecular orbitals being localized on the different branches of the cruciforms. [ABSTRACT FROM AUTHOR]

Abstract: Femtosecond transient absorption spectroscopy in the visible and NIR and ultrafast fluorescence spectroscopy were used to examine the excited state dynamics of astaxanthin and its radical cation. For neutral astaxanthin, two kinetic components corresponding to time constants of 130fs (decay of the S2 excited state) and 5.2ps (nonradiative decay of the S1 excited state) were sufficient to describe the data. The dynamics of the radical cation proved to be more complex. The main absorption band was shifted to 880nm (D0 →D3 transition), showing a weak additional band at 1320nm (D0 →D1 transition). We found, that D3 decays to the lower-lying D2 within 100fs, followed by a decay to D1 with a time constant of 0.9ps. The D1 state itself exhibited a dual behavior, the majority of the population is transferred to the ground state in 4.9ps, while a small population decays on a longer timescale of 40ps. Both transitions from D1 were found to be fluorescent. [Copyright &y& Elsevier]