The excited state dipole moment of the lowest excited singlet state of 2,3-benzofuran in ethylacetate solution is determined using thermochromic spectroscopy and compared to the values which are obtained for the isolated molecule from electronic Stark spectroscopy (Hebestreit et al., 2020) and to the results of ab initio calculations at coupled cluster level of theory. It is shown that the dipole moment from thermochromic shifts in solution deviates considerably from that of the isolated molecule. This finding can be traced back to a field induced mixing by the strong reaction field of the solvent, which exceeds the external Stark field applied in gas phase measurements by a factor of 10.000. Depending on the dipole moments of the perturbing state and its energy gap to the excited state, dipole moments from thermochromic shifts (and consequently also of solvatochromic shifts) might be considerably different to gas phase values. However, the alteration of the electronic configuration of the molecule via the reaction field of the solvent can be deperturbed in the high-field limit.

Pyridopyrimidines are heterocyclic aromatic compounds known by their antibacterial and medicinal properties. In this work, a series of pyrido[2,3-d]pyrimidine indole derivatives were synthesized by three-component one pot cyclocondensation Michael reaction between 2,6-diaminopirimidin-4(3H)-one, 3-(2-cyanoacetyl)indole and aromatic aldehydes in boiling acetic acid as solvent. The compounds differ with respect to the substituents of the aromatic aldehyde which are comprised by -C6H5, -4-ClC6H4, -4-NO2C6H4, -3,4-OCH2OC6H3, -3-OCH3,4-OH,5-NO2C6H2, and -3,4,5-tri-H3COC6H2, respectively. The compounds were synthesized with reasonable yields. They were characterized by and IR, mass, and NMR spectrometry. The protocol employed offers the convenient advantages of a one-step synthesis, considerable savings of solvents, and easy isolation of reaction products. In addition, DFT and TD-DFT quantum chemical calculations were used to characterize the geometry and electronic structure of the compounds.

Internal conversion is an inherently quantum mechanical process. To date, “ab initio” computation of internal conversion rates was limited to harmonic based approximations. These are questionable since the typical transition to the ground electronic state occurs at energies which are far from the harmonic limit. It is thus of interest to study the applicability of the Semiclassical Initial Value Representation (SCIVR) approach which is in principle amenable to “on the fly” studies even with “many” degrees of freedom. In this work we apply the Herman-Kluk-SCIVR methodology to compute the internal conversion rates for formaldehyde for a variety of initial vibronic states. The SCIVR computation gives reasonable agreement with experiment, while the harmonic approximation typically gives rates that are too high.

The UV absorption of nucleobases: semi-classical ab initio spectra simulations Mario Barbatti, Adelia J. A. Aquino and Hans Lischka, Phys. Chem. Chem. Phys., 2010. DOI: 10.1039/b924956g Vibronic coupling in indole: I. Theoretical description of the La–Lb interaction and the electronic spectrum Christian Brand, Jochen Küpper, David W. Pratt, W. Leo Meerts, Daniel Krügler, Jörg Tatchen and Michael Schmitt, Phys. Chem. Chem. Phys., 2010 DOI: 10.1039/c001776k

High-resolution electronic spectra of indole (C(8)H(7)N) and their detailed analysis are reported. Thirteen low-lying vibronic bands-from the electronic origin transition at 35 231.4 cm(-1) up to 1000 cm(-1) above-are recorded with rotational resolution. Besides inertial parameters and inertial defects these spectra yield detailed information, for each individual band, on the transition-dipole-moment orientations in the molecular inertial frame as well as on the reorientation of that inertial frame upon electronic excitation. The natural lifetimes of the individual vibronic states have also been determined. Strongly varying orientations of the transition-dipole-moments, unexpected positive inertial defects, and decreasing lifetimes, which are only partly related to increased excitation energy, are observed. These results are clear indications of the interaction of the two lowest electronically excited singlet states ((1)L(b) and (1)L(a)). Our experimental findings are strongly supported by, and in excellent agreement with, the theoretical description of the interaction of the two electronic states described in the preceding paper. These results provide clear evidence for strong vibronic coupling of the two electronic states (1)L(b) and (1)L(a) and for the energetic location of the (1)L(a)-state more than 1000 cm(-1) above the (1)L(b) vibrationless state.

Received 16 December 2009DOI:https://doi.org/10.1103/PhysRevB.81.049903©2010 American Physical Society

The anharmonic S(0)-->S(1) vibronic absorption spectrum of the formaldehyde molecule is computed on the fly using semiclassical dynamics. This first example of an on-the-fly semiclassical computation of a vibronic spectrum was achieved using a unit prefactor modified frozen Gaussian semiclassical propagator for the excited state. A sample of 6000 trajectories sufficed for obtaining a converged spectrum, which is in reasonable agreement with experiment. Similar agreement is not obtained when using a harmonic approximation for the spectrum, demonstrating the need for a full anharmonic computation. This first example provides a resolution of approximately 100 cm(-1). Potential ways of improving the methodology and obtaining higher resolution and accuracy are discussed.

Author Institution: Institut fur Physikalische Chemie I, Heinrich-Heine-Universitat; Universitatsstra{\ss}e 26.43.02.43 D-40225 Dusseldorf, Germany; Fritz-Haber-Institut der Max-Planck-Gesellschaft, 14195 Berlin, Germany; Molecular and Biophysics Group, Institute for Molecules and Materials,Radboud University; 6500 GL Nijmegen, The Netherlands; University of Pittsburgh, Department of Chemistry, Pittsburgh, PA 15260, USA; Chemical Physics Department, Weizmann Institute of Science, 76100 Rehovot, Israel; Institut fur Physikalische Chemie I, Heinrich-Heine-Universitat; Universitatsstra{\ss}e 26.43.02.43 D-40225 Dusseldorf, Germany

Extensive time-dependent DFT (TDDFT) and DFT/multireference configuration interaction (MRCI) calculations are performed on the singlet and triplet excited states of free-base porphyrin, with emphasis on intersystem crossing processes. The equilibrium geometries, as well as the vertical and adiabatic excitation energies of the lowest singlet and triplet excited states are determined. Single and double proton-transfer reactions in the first excited singlet state are explored. Harmonic vibrational frequencies are calculated at the equilibrium geometries of the ground state and of the lowest singlet and triplet excited states. Furthermore, spin-orbit coupling matrix elements of the lowest singlet and triplet states and their numerical derivatives with respect to nuclear displacements are computed. It is shown that opening of an unprotonated pyrrole ring as well as excited-state single and double proton transfer inside the porphyrin cavity lead to crossings of the potential energy curves of the lowest singlet and triplet excited states. It is also found that displacements along out-of-plane normal modes of the first excited singlet state cause a significant increase of the , , and spin-orbit coupling matrix elements. These phenomena lead to efficient radiationless deactivation of the lowest excited states of free-base porphyrin via intercombination conversion. In particular, the S1-->T1 population transfer is found to proceed at a rate of approximately 10(7) s(-1) in the isolated molecule.

Excited state potential energy hypersurfaces of 7H-furo[3,2-g][1]benzopyran-7-one (psoralen) have been explored employing (time-dependent) Kohn-Sham density functional theory. At selected points, we have determined electronic excitation energies and electric dipole (transition) moments utilizing a combined density functional/multireference configuration interaction method. Spin-orbit coupling has been taken into account employing an efficient, non-empirical spin-orbit mean-field Hamiltonian. Franck-Condon factors have been computed for vibrational modes with large displacements in the respective Dushinsky transformations. The simulated band spectra closely resemble experimental band shapes and thus validate the theoretically determined nuclear structures at the S(0), S(1), and T(1) minima. In the S(1) (pi(HOMO)-->pi*(LUMO)) state, the lactone bond of the pyrone ring is significantly elongated. From excited vibrational levels of the S(1) state a conical intersection between a (pi-->sigma*) excited state and the electronic ground state may be energetically accessible. Fast non-radiative decay via this relaxation pathway could explain the low fluorescence quantum yield of psoralen. The T(1) (pi(HOMO-1)-->pi*(LUMO)) exhibits a diradicaloid electronic structure with a broken C(5)-C(6) double bond in the pyrone ring. A variational multireference spin-orbit configuration interaction procedure yields a phosphorescence lifetime of 3 s, in excellent agreement with experimental estimates.