Klaus Gustav

THEORETICAL INVESTIGATIONS ON ABSORPTION AND FLUORESCENCE OF PERYLENE AND ITS TETRACARBOXYLIC DERIVATIVES

SummaryTheoretical molecular geometries of the perylene derivatives 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA), 3,4,9,10-perylene tetracarboxylic diimide (PTCDI), N,N′-dimethyl 3,4,9,10-perylene tetracarboxylic diimide (MePTCDI), and 3,4,9,10-perylene tetracarboxylic disulfide (PTCDS) are presented for the electronic statesS0 andS1. On this basis, the electronic absorption properties can be interpreted and compared with experimentel data. The vibronic structure ofS0 →S1 absorption andS1 →S0 fluorescence has been reproduced. The analysis of the active vibrational modes shows a corresponding behaviour of derivatives and perylene.ZusammenfassungTheoretische Molekülgeometrien der Perylen-Derivate 3,4,9,10-Perylentetracarbonsäuredianhydrid (PTCDA), 3,4,9,10-Perylentetracarbonsäurediimid (PTCDI), N,N′-Dimethyl-3,4,9,10-Perylentetracarbonsäurediimid (MePTCDI) und 3,4,9,10-Perylentetracarbonsäuredisulfid (PTCDS) für die elektronischen ZuständeS0 undS1 werden vorgestellt. Auf dieser Grundlage können die elektronischen Absorptionseigenschaften interpretiert und mit experimentellen Daten verglichen werden. Die vibronische Struktur derS0 →S1-Absorption und derS1 →S2-Fluoreszenz konnte reproduziert werden. Die Analyse der aktiven Schwingungsmoden zeigen ein gegenüber Perylen vergleichbares Verhalten der Derivate.

Molecular geometry and excited electronic states. Theoretic study on the molecular geometry and the fluorescence lifetime difference of isometric phenylnapkthalenes

Abstract The equilibrium molecular geometries of 1-phenyl- and 2-phenyl-naphthalenes in the electronic So and S1 states have been calculated by minimization of the total energy with respect to all molecular coordinates. The singlet term systems of both isomers have been determined using these results. Although the fluorescence transition energy is nearly the same in both cases it was found that the corresponding electronic transitions were allowed in 1-phenylnaphthalene but were forbidden in 2-phenylnaphthalene. The result explains the different fluorescence lifetimes observed.

Determination of reaction quantum yields of photochromic fulgides using mid-IR spectroscopy: quantitative evaluation and normal mode analysis

Abstract To demonstrate the feasibility of non-destructive readout of optically recorded data using IR absorption spectroscopy [1] , the ring-closure/ring-opening reactions of photochromic fulgides are monitored without perturbation, and the respective reaction quantum yields are determined quantitatively. The values are identical to those determined from UV/VIS spectroscopy. Variation of substituents and a normal mode analysis based on semi-empirical QCFF/PI calculations reveal the nature of the vibrational modes relevant for the method, thus helping to understand the underlying mechanisms.

Spektroskopische Untersuchungen an organischen Carbonylverbindungen, 5. Mitt.: Zum Einfluß des π-Chromophors auf das elektronische Spektralverhalten von dimethylaminophenyl-substituierten β-Diketonen bei Kettenverlängerung und Variation der Arylsubstituenten

SummaryAbsorption and fluorescence data of dimethylaminophenyl-substituted β-dicarbonyl compounds are discussed in dependence on the size of the π-electronic system. The variation of the chain length and of the aryl moiety shows the strong influence of the intramolecular donor-acceptor properties on the deactivation processes. The stabilization of the S1-state in polar solvents gives rise to fluorescences with large Stokes shifts.

Vibronic spectral behaviour of molecules. Theoretical analysis of the biphenyl phosphorescence

Abstract The calculated vibronic structure of the phosphorescence of biphenyl is presented and compared with the experimental spectrum. An assignment of the vibronic transitions for the main peaks is given. The comparison between theory and experiment is satisfactory.

Quantum chemical studies on colour and stereodynamics of acyclic azines: Part XI. The model of the “crank-shaft” mechanism for (E, Z) isomerization of arylsubstituted acyclic azines☆

Abstract A new mechanism called the “crank-shaft” mechanism (“Kurbelwellen”-Mechanismus), based on the concept of motion processes through multiple-coupled structural variables, is proposed for the ( E , Z ) isomerization of the arylsubstituted acyclic azines in different media. The mathematical model is presented. The isomerization quantum yields are of a comparable order of magnitude for these compounds and are included in the discussion of the mechanism.

Theoretical study of the kinetic isotope effect in proton-transfer reactions. Influence of the interaction potential of reactants on the kinetic isotope effect

Abstract The dependence of the kinetic isotope effect of proton-transfer reactions on the shape of the interaction potential of reactants is investigated within the framework of the quantum-statistical mechanical theory of rate processes for polar media. It is shown that the assumption of equal transfer distances for H + and D + is not justified for realistic interaction potentials. The difference of the transfer distances exhibits a maximum in passing from flat to steep potentials. The results obtained are discussed with regard to the influence on steric hindrance and hydrogen bonding. The influence of the interaction potential between the reactants on the kinetic isotope effect was investigated utilizing the quantum-statistical mechanical theory of rate processes in polar media for reactions with Δ E = 0 and T = 300 K. It was found that the difference of the effective transfer distances r 00 H − r 00 D exhibits a maximum in passing from very flat to steep potentials. The assumption r 00 H = r 00 D is not justified for realistic interaction potentials. The kinetic isotope effect is very sensitive to variations in the intermolecular potential. The isotope effect should be increased by steric hindrance and decreased by hydrogen bonding of the reactants. The first result is supported by experimental facts the second one requires further experimental efforts. After submission of the present work calculations on the KIE using a Morse intermolecular potential were published [37]. It has also been found that the assumption r 00 H = r 00 D is not justified for realistic interaction potentials. The calculations in ref. [37] are restricted to several sets of potential parameters all reproducing the same value of a KIE observed experimentally. The effect of a systematic variation of the potential shape was not investigated.

Interpretation of the vibrational spectra and calculation of the geometries of cycloheptatriene, 7-d-cycloheptatriene and phenyl substituted cycloheptatrienes

Abstract Equilibrium geometries, vibrational frequencies and normal coordinates have been calculated quantum chemically for the strained ring compound cycl oheptatriene and its phenyl substituted derivatives. The calculated geometry of cycloheptatriene agrees with the experimental one. The 1-, 2- and 3-phenyl substituted derivatives have a more nearly planar shape for the seven membered ring than cycloheptatriene itself. Comparison with the experimental vibrational frequencies of cycloheptatriene and 7-d-cycloheptatriene results in a satisfactory interpretation of the vibrational spectra. The three carbon—carbon stretching frequencies of the cycloheptatriene π-system show only minor effects caused by phenyl substitution.

Molekülgeometrie und angeregte Elektronenzustände, XXII: Quantenchemische Untersuchungen zur Molekülgeometrie und zum vibronischen Spektralverhalten von ausgewählten Borchelaten

SummaryThe theoretical completely-optimized molecular geometries of selected boron chelates calculated by means of the semi-empirical Warshel-Karplus method, are presented for the electronic states S0, S1 and T1. On this basis the vibronic spectral behaviour in absorption, fluorescence and phosphorescence has been determined by computing the Franck-Condon weighted density functions within the framework of the Condon approximation. The theoretical results obtained are compared with the experimental S1 ← S0 absorption, S1 → S0 fluorescence and T1 → S0 phosphorescence, and interpreted with respect to the active vibrational modes. The calculated geometry changes are found to be largely attributed to those modes responsible for the fine structure of the corresponding spectroscopic transitions.

Theory of proton-transfer reactions. The influence of adiabaticity on free energy relations

Abstract The influence of adiabaticity on free energy relations of proton-transfer reactions is investigated within the framework of the quantum-statistical mechanical rate theory. It is found that there may be both for the Bronsted plot and for the free energy dependence of the kinetic isotope effect qualitative differences between the non-adiabatic and the adiabatic case in the exergonic region.