Academic Appointments


Professional Education


  • Dr. rer. nat., Technische Universität München (2014)
  • Diplom-Chemiker, Philipps-Universität Marburg (2009)

All Publications


  • Nonadiabatic dynamics simulations of photoexcited urocanic acid CHEMICAL PHYSICS Tuna, D., Spoerkel, L., Barbatti, M., Thiel, W. 2018; 515: 521–34
  • The Spin-Flip Variant of the Algebraic-Diagrammatic Construction Yields the Correct Topology of s(1)/S-0 Conical Intersections JOURNAL OF CHEMICAL THEORY AND COMPUTATION Lefrancois, D., Tuna, D., Martinez, T. J., Dreuw, A. 2017; 13 (9): 4436–41

    Abstract

    While the conventional variants of the algebraic-diagrammatic construction (ADC) scheme for the polarization propagator are generally incapable of correctly describing the topology of S1/S0 conical intersections (CIs), its corresponding spin-flip (SF) variant of third-order ADC (ADC(3)) is herein demonstrated to successfully reproduce the S1/S0 minimum-energy CI (MECI) of twisted formaldinium (H2C═NH2+). Analytical nuclear excited-state gradients of ADC have been used in combination with the CIOpt program for the optimization of the MECI without the need for nonadiabatic-coupling vectors. For comparison, MS-CASPT2 calculations were performed via conventional CI optimization employing analytical nonadiabatic-coupling vectors. It is shown that SF-ADC(3) yields the correct dimensionality of the CI and overall compares very favorably to the MS-CASPT2 results.

    View details for PubMedID 28742963

  • Conical-Intersection Topographies Suggest That Ribose Exhibits Enhanced UV Photostability JOURNAL OF PHYSICAL CHEMISTRY B Tuna, D., Sobolewski, A. L., Domcke, W. 2016; 120 (41): 10729–35
  • Semiempirical Quantum-Chemical Orthogonalization-Corrected Methods: Benchmarks of Electronically Excited States JOURNAL OF CHEMICAL THEORY AND COMPUTATION Tuna, D., Lu, Y., Koslowski, A., Thiel, W. 2016; 12 (9): 4400–4422

    Abstract

    The semiempirical orthogonalization-corrected OMx methods have recently been shown to perform well in extensive ground-state benchmarks. They can also be applied to the computation of electronically excited states when combined with a suitable multireference configuration interaction (MRCI) treatment. We report on a comprehensive evaluation of the performance of the OMx/MRCI methods for electronically excited states. The present benchmarks cover vertical excitation energies, excited-state equilibrium geometries (including an analysis of significant changes between ground- and excited-state geometries), minimum-energy conical intersections, ground- and excited-state zero-point vibrational energies, and 0-0 transition energies for a total of 520 molecular structures and 412 excited states. For comparison, we evaluate the TDDFT/B3LYP method for all benchmark sets, and the CC2, MRCISD, and CASPT2 methods for some of them. We find that the current OMx/MRCI methods perform reasonably well for many of the excited-state properties. However, in comparison to the first-principles methods, there are also a number of shortcomings that should be addressed in future developments.

    View details for DOI 10.1021/acs.jctc.6b00403

    View details for Web of Science ID 000383315700022

    View details for PubMedID 27380455

  • Comparative study of radiationless deactivation mechanisms in cytosine and 2,4-diaminopyrimidine JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY Kancheva, P., Tuna, D., Delchev, V. B. 2016; 321: 266–74
  • Onset of the Electronic Absorption Spectra of Isolated and pi-Stacked Oligomers of 5,6-Dihydroxyindole: An Ab Initio Study of the Building Blocks of Eumelanin JOURNAL OF PHYSICAL CHEMISTRY B Tuna, D., Udvarhelyi, A., Sobolewski, A. L., Domcke, W., Domratcheva, T. 2016; 120 (14): 3493–3502

    Abstract

    Eumelanin is a naturally occurring skin pigment which is responsible for developing a suntan. The complex structure of eumelanin consists of π-stacked oligomers of various indole derivatives, such as the monomeric building block 5,6-dihydroxyindole (DHI). In this work, we present an ab initio wave-function study of the absorption behavior of DHI oligomers and of doubly and triply π-stacked species of these oligomers. We have simulated the onset of the electronic absorption spectra by employing the MP2 and the linear-response CC2 methods. Our results demonstrate the effect of an increasing degree of oligomerization of DHI and of an increasing degree of π-stacking of DHI oligomers on the onset of the absorption spectra and on the degree of red-shift toward the visible region of the spectrum. We find that π-stacking of DHI and its oligomers substantially red-shifts the onset of the absorption spectra. Our results also suggest that the optical properties of biological eumelanin cannot be simulated by considering the DHI building blocks alone, but instead the building blocks indole-semiquinone and indole-quinone have to be considered as well. This study contributes to advancing the understanding of the complex photophysics of the eumelanin biopolymer.

    View details for DOI 10.1021/acs.jpcb.6b01793

    View details for Web of Science ID 000374431000004

    View details for PubMedID 27005558

  • Excited-state deactivation in 8-oxo-deoxyguanosine: comparison between anionic and neutral forms PHYSICAL CHEMISTRY CHEMICAL PHYSICS Tuna, D., Domcke, W. 2016; 18 (2): 947–55

    Abstract

    8-Oxoguanine is the most abundant oxidation product found in oxidatively damaged DNA. The study of the excited-state properties of the corresponding deoxyribonucleoside 8-oxo-deoxyguanosine is thus of important biological relevance. Herein, we present an ADC(2)-s ab initio study of the neutral and the anionic form of 8-oxo-deoxyguanosine, for each of which we have considered the intramolecularly 5'-O-H···N3 hydrogen-bonded syn conformer. We present energy profiles for a radiationless deactivation mechanism via intramolecular excited-state proton transfer. This mechanism is accessible in the neutral form, but it is unavailable in the anion. We present optimized structures for the proton-transfer conical intersection of the neutral form as well as the ring-puckered conical intersections inherent to the 8-oxoguanine moiety for the neutral and anionic forms. We highlight the possible relevance of the proton-transfer mechanism for the neutral form and discuss our results in light of several recently published computational and spectroscopic studies. Our results provide new insight into the photophysics of this biologically relevant nucleoside and pave the way for future nonadiabatic dynamics studies and for further spectroscopic investigations.

    View details for DOI 10.1039/c5cp05804j

    View details for Web of Science ID 000369480600034

    View details for PubMedID 26650478

  • Assessment of Approximate Coupled-Cluster and Algebraic-Diagrammatic-Construction Methods for Ground- and Excited-State Reaction Paths and the Conical-Intersection Seam of a Retinal-Chromophore Model JOURNAL OF CHEMICAL THEORY AND COMPUTATION Tuna, D., Lefrancois, D., Wolanski, L., Gozem, S., Schapiro, I., Andruniow, T., Dreuw, A., Olivucci, M. 2015; 11 (12): 5758–81

    Abstract

    As a minimal model of the chromophore of rhodopsin proteins, the penta-2,4-dieniminium cation (PSB3) poses a challenging test system for the assessment of electronic-structure methods for the exploration of ground- and excited-state potential-energy surfaces, the topography of conical intersections, and the dimensionality (topology) of the branching space. Herein, we report on the performance of the approximate linear-response coupled-cluster method of second order (CC2) and the algebraic-diagrammatic-construction scheme of the polarization propagator of second and third orders (ADC(2) and ADC(3)). For the ADC(2) method, we considered both the strict and extended variants (ADC(2)-s and ADC(2)-x). For both CC2 and ADC methods, we also tested the spin-component-scaled (SCS) and spin-opposite-scaled (SOS) variants. We have explored several ground- and excited-state reaction paths, a circular path centered around the S1/S0 surface crossing, and a 2D scan of the potential-energy surfaces along the branching space. We find that the CC2 and ADC methods yield a different dimensionality of the intersection space. While the ADC methods yield a linear intersection topology, we find a conical intersection topology for the CC2 method. We present computational evidence showing that the linear-response CC2 method yields a surface crossing between the reference state and the first response state featuring characteristics that are expected for a true conical intersection. Finally, we test the performance of these methods for the approximate geometry optimization of the S1/S0 minimum-energy conical intersection and compare the geometries with available data from multireference methods. The present study provides new insight into the performance of linear-response CC2 and polarization-propagator ADC methods for molecular electronic spectroscopy and applications in computational photochemistry.

    View details for DOI 10.1021/acs.jctc.5b00022

    View details for Web of Science ID 000366223400019

    View details for PubMedID 26642989

  • Mechanisms of Photostability in Kynurenines: A Joint Electronic-Structure and Dynamics Study JOURNAL OF PHYSICAL CHEMISTRY B Tuna, D., Doslic, N., Malis, M., Sobolewski, A. L., Domcke, W. 2015; 119 (6): 2112–24

    Abstract

    Kynurenines are UV filters found in the human ocular lens which protect the retina from radiation damage. We report on ab initio investigations of the photochemistry of the cis and trans conformers of kynurenine and of an intramolecularly hydrogen-bonded conformer of 3-hydroxykynurenine O-β-D-glucoside. We have explored the excited-state reaction paths for several radiationless excited-state deactivation processes in kynurenines. We show that electron-driven proton-transfer processes mediated by an excited state of charge-transfer character exhibit negligible barriers and that the relevant potential-energy profiles are lower in energy than the lowest absorbing ππ* state. In these proton-transfer processes, a proton moves from one of the amino groups of kynurenine to the keto group. We also report on nonadiabatic trajectory-surface-hopping molecular-dynamics simulations for photoexcited kynurenine. These simulations show that the cis and trans conformers of kynurenine deactivate on a femtosecond-to-picosecond time scale preferably via electron-driven proton transfer from one of the amino groups to the keto group. Cis kynurenine deactivates via a ring-N-H···O═C proton-transfer process. Trans kynurenine tends to undergo trans → cis isomerization before deactivating via the same process. These results suggest that the deactivation process involving the ring-amino group in the cis conformer of kynurenine is the most efficient excited-state deactivation process in kynurenines. The joint electronic-structure calculations and dynamics simulations provide a new level of mechanistic insight into the efficient UV-filtering capacity of kynurenines.

    View details for DOI 10.1021/jp501782v

    View details for Web of Science ID 000349578600004

    View details for PubMedID 25054917

  • Photoinduced water splitting via benzoquinone and semiquinone sensitisation PHYSICAL CHEMISTRY CHEMICAL PHYSICS Karsili, T. V., Tuna, D., Ehrmaier, J., Domcke, W. 2015; 17 (48): 32183–93

    Abstract

    The splitting of water into H˙ and OH˙ radicals by sensitisation of a redox-active chromophore with sunlight may eventually become a viable way of producing unlimited, clean and sustainable energy. In this work, we explore the possibility of photo-oxidation of water via sensitisation of benzoquinone with ultraviolet (UV) light in the hydrogen-bonded complex of benzoquinone with a single water molecule. Using state-of-the-art quantum chemical calculations, the mechanisms of electron/proton transfer reactions between photoexcited benzoquinone and water are characterised. In the benzoquinone-H2O complex, photoexcitation of the chromophore leads to the population of locally excited ππ* and nπ* singlet states, which are coupled to hitherto unknown charge-transfer states. In the latter, an electron is transferred from the oxygen atom of the water molecule to the lowest π* orbital of benzoquinone. These charge-separated states drive the transfer of a proton from the water molecule to the carbonyl acceptor site, yielding the semiquinone-OH˙ biradical. Upon absorption of a second UV photon, the semiquinone radical may undergo O-H bond fission, which generates an H˙ radical and restores the benzoquinone photocatalyst. Our computational results shed light on long-standing questions regarding the nature of the photoreactive electronic states in the aqueous photochemistry of benzoquinone.

    View details for DOI 10.1039/c5cp03831f

    View details for Web of Science ID 000365954700012

    View details for PubMedID 26488227

  • Photochemical Mechanisms of Radiationless Deactivation Processes in Urocanic Acid JOURNAL OF PHYSICAL CHEMISTRY B Tuna, D., Sobolewski, A. L., Domcke, W. 2014; 118 (4): 976–85

    Abstract

    Urocanic acid is a UV filter found in human skin that protects the skin from UV damage but has also been linked to the onset of skin cancer and to photoimmunosuppression. We report on ab initio investigations of two rotameric forms of each of the two tautomers of neutral (E)- and (Z)-urocanic acid. We have computed the vertical singlet excitation energies of eight isomers and have explored the singlet excited-state reaction paths of several photochemical processes for radiationless excited-state deactivation: the E/Z photoisomerization, an electron-driven proton transfer for an intramolecularly hydrogen-bonded Z isomer, as well as the hydrogen-atom detachment process and the ring-puckering process involving the NH group inherent to the imidazole moiety. We have optimized the S1/S0 conical intersections for each of these processes and located additional ππ*/nπ* conical intersections. Because of the reversed energetic order of the nπ* and ππ* states in the N3H and N1H tautomers, an energy window exists where the N3H tautomers can be excited to the nπ* state, from which only the photoisomerization process is accessible, while the N1H tautomers can be excited to the ππ* state, from which several deexcitation processes compete from the onset of the absorption. These results explain the unusual dependence of the quantum yield for E→Z photoisomerization on the excitation wavelength. The present work provides novel insight into the complex photochemistry of this biomolecule and paves the way for future computational studies of the photoinduced excited-state dynamics of urocanic acid.

    View details for DOI 10.1021/jp411818j

    View details for Web of Science ID 000330610400013

    View details for PubMedID 24397532

  • Mechanisms of Ultrafast Excited-State Deactivation in Adenosine JOURNAL OF PHYSICAL CHEMISTRY A Tuna, D., Sobolewski, A. L., Domcke, W. 2014; 118 (1): 122–27

    Abstract

    Recently, resonant two-photon ionization experiments on isolated adenine and adenosine suggested that adenosine exhibits a significantly shorter excited-state lifetime than adenine, which indicates the existence of an efficient excited-state deactivation mechanism in adenosine that is not existent in adenine. We report on ab initio investigations on a syn and an anti conformer of adenosine exhibiting an intramolecular O-H···N3 hydrogen bond. For both conformers, we have identified the existence of a barrierless excited-state deactivation mechanism that involves the forward-backward transfer of a proton along the intramolecular hydrogen bond and ultrafast radiationless deactivation through conical intersections. The S1/S0 conical intersection associated with the proton-transfer process is lower in energy than the known S1/S0 conical intersections associated with the excited-state deactivation processes inherent to the adenine moiety. These results support the conjecture that the photochemistry of hydrogen bonds plays a decisive role for the photostability of the molecular building blocks of RNA and DNA, which have been selected at the earliest stages of the chemical evolution of life.

    View details for DOI 10.1021/jp410121h

    View details for Web of Science ID 000329678100015

    View details for PubMedID 24320624

  • Electronically excited states and photochemical reaction mechanisms of beta-glucose PHYSICAL CHEMISTRY CHEMICAL PHYSICS Tuna, D., Sobolewski, A. L., Domcke, W. 2014; 16 (1): 38–47

    Abstract

    Carbohydrates are important molecular components of living matter. While spectroscopic and computational studies have been performed on carbohydrates in the electronic ground state, the lack of a chromophore complicates the elucidation of the excited-state properties and the photochemistry of this class of compounds. Herein, we report on the first computational investigation of the singlet photochemistry of β-glucose. It is shown that low-lying singlet excited states are of nσ* nature. Our computations of the singlet vertical excitation energies predict absorption from 6.0 eV onward. Owing to a dense manifold of weakly-absorbing states, a sizable and broad absorption in the ultraviolet-C range arises. We have explored two types of photochemical reaction mechanisms: hydrogen-detachment processes for each of the five O-H groups and a C-O ring-opening process. Both types of reactions are driven by repulsive nσ* states that are readily accessible from the Franck-Condon region and lead to conical intersections in a barrierless fashion. We have optimized the geometries of the conical intersections involved in these photochemical processes and found that these intersections are located around 5.0 eV for the O-H hydrogen-detachment reactions and around 4.0 eV for the C-O ring-opening reaction. The energies of all conical intersections are well below the computed absorption edge. The calculations were performed using linear-response methods for the computation of the vertical excitation energies and multiconfigurational methods for the optimization of conical intersections and the computation of energy profiles.

    View details for DOI 10.1039/c3cp52359d

    View details for Web of Science ID 000327667500004

    View details for PubMedID 23959595

  • Photochemistry of 2-Aminooxazole, a Hypothetical Prebiotic Precursor of RNA Nucleotides JOURNAL OF PHYSICAL CHEMISTRY LETTERS Szabla, R., Tuna, D., Gora, R. W., Sponer, J., Sobolewski, A. L., Domcke, W. 2013; 4 (16): 2785–88

    View details for DOI 10.1021/jz401315e

    View details for Web of Science ID 000323300900032

  • Computational Study of the Mechanism of Cyclic Acetal Formation via the Iridium(I)-Catalyzed Double Hydroalkoxylation of 4-Pentyn-1-ol with Methanol ORGANOMETALLICS Fjermestad, T., Ho, J. H., Macgregor, S. A., Messerle, B. A., Tuna, D. 2011; 30 (3): 618–26

    View details for DOI 10.1021/om1009582

    View details for Web of Science ID 000286915100032