In memory of Professor Andrzej Tramer (1930–2014)

W dniu 19 listopada 2014 r. we Wrocławiu zmarł profesor Andrzej Tramer, fizykochemik. Zajmował się spektroskopią i fotofizyką molekularną, szczególnie dużo uwagi poświęcając ścieżkom dezaktywacji elektronowo wzbudzonych stanów molekularnych. Pracował w Polsce i we Francji. Poniżej kilka słów o jego wkładzie w rozwój nauki oraz o śladach, jakie pozostawił w naszej pamięci.On November 19, 2014 in Wroclaw died Professor Andrzej Tramer, physical chemist. He was involved in molecular spectroscopy and photophysics, devoting particular attention to deactivation pathways of electronic excited states of molecules. He worked in Poland and France. Here are a few words about his contribution to the development of science and the traces left in our memory

Spectroscopy and Photophysics of Monoazaphenanthrenes II. Ab initio Analysis of Molecular Parameters and Electronic Spectra

The ground state structures of phenanthrene and its monoaza-deriv atives, phenanthridine and 7,8-benzoquinoline were optimized using the ab initio methods. Both methods of optimization are leading to the results, which are in good agreement with available experimental data. Calculated ground-state electric dipole moments in phenanthridine and 7,8-benzoquinoline were found to have antiparallel orientations, due to the different electronic charge distributions in these molecules. The energies of vertical electronic transitions from the ground to excited singlet states (S$\text{}_{0}$ → S$\text{}_{n}$ transitions) and the corresponding oscillator strengths were calculated within the framework of configuration interaction-singles and time-dependent density functional theory. The last method was found to be more accurate in reproduction of experimental absorption spectra. Very interesting result of these computations is the change of relative orientation of the transition dipole moments for the two lowest ππ* electronic transition in monoazaphenanthrenes - from perpendicular in phenanthrene molecule to nearly parallel orientation in both monoazaphenanthrenes. The observed changes of molecular parameters and spectra can be related to the inductive effects of the substitution of nitrogen atom into the aromatic skeleton of phenanthrene

Analysis of the Origin Band of Acridine Dimer Fluorescence Excitation Spectrum - Conformations of Jet-Cooled Acridine Dimer

The analysis of rotational band contour for the origin transition of fluorescence excitation spectrum of acridine dimer, earlier observed under conditions of jet-cooling in supersonic helium expansion, has been performed. An optimized ground-state equilibrium structure of acridine dimer fits the approximation of asymmetric top rigid rotor. In this approximation rotational constants were determined and an A-type rotational band was computed. It has turned out that the computed rotational band contour is much narrower than the experimental one. In search for the reasons of this discrepancy between calculations and experiment, an analysis of relative rotational motion of acridine moieties of the dimer was carried out. It was found that minima of potential energy curves for rotational motion, although very flat, under conditions of supersonic expansion can acquire (in their shallow local minima) non-vanishing population of slightly different conformations of the dimer. It was shown that in terms of non-statistical distribution of such populations, the origin bands of individual conformations may contribute to the experimental band contour

Normal Mode Analysis of Vibrations of Jet-Cooled Acridine Dimer

The analysis of normal modes of vibrations was performed for acridine dimer, which has been recently observed and identified by laser-induced emission spectroscopy under conditions of jet-cooling in a supersonic helium expansion. The frequencies and the forms of normal vibrations, computed with the use of the semi-empirical PM3 method are classifying all vibrations of acridine dimer into two distinct categories of inter- and intramolecular vibrations. There are six low-frequency intermolecular normal vibrations which are characterizing relative movements of two acridine moieties in the dimer and at least two of them have vibrational frequencies which are close to the frequencies of vibronic bands observed in the fluorescence excitation spectrum of the dimer. The intramolecular normal vibrations of the dimer very strictly correspond to the normal vibrations of acridine molecule (with a minor modification of the vibrational frequencies due to the splitting in the dimer). Furthermore, the intramolecular vibrations of acridine dimer, as well as the vibrations of acridine molecule are in good agreement with available experimental data (either IR and Raman spectra of acridine or fluorescence excitation spectrum of acridine dimer in supersonic jet). The results of the present analysis are very clearly supporting the previous conclusions concerning the ground-state equilibrium structure of acridine dimer formed under jet-cooling conditions

Spectroscopy and Photophysics of Monoazaphenanthrenes II. Ab initio Analysis of Molecular Parameters and Electronic Spectra

The ground state structures of phenanthrene and its monoaza-deriv atives, phenanthridine and 7,8-benzoquinoline were optimized using the ab initio methods. Both methods of optimization are leading to the results, which are in good agreement with available experimental data. Calculated ground-state electric dipole moments in phenanthridine and 7,8-benzoquinoline were found to have antiparallel orientations, due to the different electronic charge distributions in these molecules. The energies of vertical electronic transitions from the ground to excited singlet states (S$\text{}_{0}$ → S$\text{}_{n}$ transitions) and the corresponding oscillator strengths were calculated within the framework of configuration interaction-singles and time-dependent density functional theory. The last method was found to be more accurate in reproduction of experimental absorption spectra. Very interesting result of these computations is the change of relative orientation of the transition dipole moments for the two lowest ππ* electronic transition in monoazaphenanthrenes - from perpendicular in phenanthrene molecule to nearly parallel orientation in both monoazaphenanthrenes. The observed changes of molecular parameters and spectra can be related to the inductive effects of the substitution of nitrogen atom into the aromatic skeleton of phenanthrene

Photoinduced Charge-Transfer Reactions of Tricyanoethylene with Aromatic Hydrocarbon Electron Donors. II. Semiempirical Studies of Naphthalene-Tricyanoethylene Exciplex

In this work we present the results of semiempirical AM1 calculations of the energy of electron-donor-acceptor system of naphthalene-tricyanoethylene complex in the ground and excited state with full optimization of the complex geometry. It was found that a ground state of the complex under consideration is stabilized almost exclusively by the electrostatic and Van der Waals interactions (presumably without charge-transfer resonance interaction). Its optimized equilibrium configuration has almost perpendicular head-to-face orientation of component molecules while in an excited state it is practically a charge-transfer electronic configuration with almost sandwich-like arrangement of both molecules. The energies of vertical electronic transitions between relevant ground and excited states and other spectroscopic parameters for these transitions were calculated with the use of ZINDO/S method and were compared with results of recent experimental observations of naphthalene-tricyanoethylene exciplex. This comparison led to a satisfactory explanation of the spectral properties and to a deeper insight into the kinetic parameters of the electron-donor-acceptor system under study

Excited States of Intermolecular Electron-Donor-Acceptor Systems and Internal Geometry of Complex' Components

In this work we present the results of semiempirical AM1 calculations of the energy of electron-donor-acceptor system in the ground and excited states with full optimization of the complex geometry (in terms of both: intermolecular and intramolecular coordinates). A comparison of these results with those obtained for separated acceptor and donor molecules enables the estimation of the energetic effects of changes in internal structure of donor and acceptor which accompany the process of formation and stabilization of excited charge-transfer state. It is shown that energies corresponding to those changes are comparable with the energy of intermolecular interactions between donor and acceptor molecules

Analysis of the Origin Band of Acridine Dimer Fluorescence Excitation Spectrum - Conformations of Jet-Cooled Acridine Dimer

The analysis of rotational band contour for the origin transition of fluorescence excitation spectrum of acridine dimer, earlier observed under conditions of jet-cooling in supersonic helium expansion, has been performed. An optimized ground-state equilibrium structure of acridine dimer fits the approximation of asymmetric top rigid rotor. In this approximation rotational constants were determined and an A-type rotational band was computed. It has turned out that the computed rotational band contour is much narrower than the experimental one. In search for the reasons of this discrepancy between calculations and experiment, an analysis of relative rotational motion of acridine moieties of the dimer was carried out. It was found that minima of potential energy curves for rotational motion, although very flat, under conditions of supersonic expansion can acquire (in their shallow local minima) non-vanishing population of slightly different conformations of the dimer. It was shown that in terms of non-statistical distribution of such populations, the origin bands of individual conformations may contribute to the experimental band contour

Fluorescence Spectra of 7,8-Benzoquinoline Isolated in the Supersonic Jet Expansion - An Ab Initio Analysis

The optimized equilibrium geometry of 7,8-benzoquinoline molecule in its first excited, S$\text{}_{1}$, singlet state was computed with the use of ab initio RCIS/6-31G(d) method. It was found that the electronic transition to the first excited state in 7,8-benzoquinoline is not confined to the neighborhood of nitrogen atom, but is delocalized over entire aromatic rings system, much alike in the molecule of phenanthrene. With the optimized geometry of the ground and excited state of the molecule, the frequencies of the vibrational fundamental modes were computed, together with their displacement parameters (geometry changes of vibrations between the excited and the ground state). These frequencies are in good agreement with vibrational frequencies present in the fluorescence spectrum of 7,8-benzoquinoline observed recently under jet-cooling conditions in supersonic beam expansion. In comparison to the fluorescence spectrum of phenanthrene, the calculated, as well as experimental fluorescence spectra of 7,8-benzoquinoline contain much more vibrational features, and this increased vibronic activity is related to the symmetry break caused by the introduction of N-heteroatom into the aromatic ring system of phenanthrene

Fluorescence Spectra of 7,8-Benzoquinoline Isolated in the Supersonic Jet Expansion - An Ab Initio Analysis

The optimized equilibrium geometry of 7,8-benzoquinoline molecule in its first excited, S$\text{}_{1}$, singlet state was computed with the use of ab initio RCIS/6-31G(d) method. It was found that the electronic transition to the first excited state in 7,8-benzoquinoline is not confined to the neighborhood of nitrogen atom, but is delocalized over entire aromatic rings system, much alike in the molecule of phenanthrene. With the optimized geometry of the ground and excited state of the molecule, the frequencies of the vibrational fundamental modes were computed, together with their displacement parameters (geometry changes of vibrations between the excited and the ground state). These frequencies are in good agreement with vibrational frequencies present in the fluorescence spectrum of 7,8-benzoquinoline observed recently under jet-cooling conditions in supersonic beam expansion. In comparison to the fluorescence spectrum of phenanthrene, the calculated, as well as experimental fluorescence spectra of 7,8-benzoquinoline contain much more vibrational features, and this increased vibronic activity is related to the symmetry break caused by the introduction of N-heteroatom into the aromatic ring system of phenanthrene