Norbert Detzer

Deviations from Kleinman symmetry of the second-order polarizability tensor in molecules with low-lying perpendicular electronic bands

Abstract 4-Nitroaniline (pNA) and 3,5-dinitro-aniline (3,5-DNA) were studied by electric field induced second harmonic generation (EFISH) and electrooptical absorption measurements (EOAM) in dioxane solution at T = 298 K. The measurements were carried out for two polarization conditions, the electric field vector of the linearly polarized incident light being parallel or perpendicular to the static electric field. The second-order polarizability tensor of pNA is confirmed to be Kleinman symmetric, while a strong deviation from index permutation symmetry is observed for 3,5-DNA. The latter is quantitatively interpreted by contributions of a low-lying electronic band with transition dipole perpendicular to the symmetry axis. New design possibilities for second-order nonlinear optical materials are pointed out.

Excited state dipole moments and polarizabilities of centrosymmetric and dimeric molecules. I. Model study of a bichromophoric molecule

Abstract Refractometric, dielectric and electro-optical absorption measurements are reported for 1-dimethylamino-2,6-dicyano-4-methyl-benzene (I) and 1,4-bis(4′-dimethylamino-3′,5′-dicyanophenyl)bicyclo[2.2.2]octane (II). The evaluation leads to dipole moments and polarizabilities of the ground state as well as the first dipole allowed singlet state. The experimental res excellently substantiate the method of electro-optical absorption measurements in solution. It is shown that the excited dimer wavefunctions of the bichromophoric molecule II localize by solvent induced local site perturbations.

Gas-phase dipole moments of molecules in their fluorescent state

Abstract The effect of an external electric field on the fluorescence of molecules in the gas phase as well as in solutions is studied and the permanent dipole moments of 9-cyanoanthracene and 2,6-N,N-tetramethyl-4-cyanoaniline (TMCA) in their fluorescent states have been determined from such investigations. By comparison of the gas-phase and liquid-phase dipole moments, it could be shown that the Onsager model is adequate to describe the effective electric field, and the polarizability density related to the molecular volume could be determined. The values of the gas-phase and of the solution effective dipole moments of TMCA oppose the solute-solvent exciplex model and favour an emitting internal charge-transfer state.

Excited state dipole moments and polarizabilities of centrosymmetric and dimeric molecules. II. Polyenes, polyynes and cumulenes

Abstract Electro-optical absorption spectra are measured for a series of polyenes, polyynes and cumulenes with centrosymmetric π-chromophores in cyclohexane solution at 298 K. For all molecules the long-axis component of the polarizability tensor is considerably larger in the first dipole-allowed singlet state compared to the ground state. The transition moments are found to be parallel to the long molecular axis. All polyenes and one cumulene show a linear Stark component indicating a long-axis excited state dipole moment. Both the dipole moments and the polarizabilities are corrected within the extended Onsager model for solvent cavity and reaction field effects. It is suggested that symmetry lowering solvent perturbations are the reason for the apparent excited state dipole moments.

Solvent dependence of effective S1 torsional potentials in 9,9′-bianthryl and 9-phenylanthracene

Optical fluorescence spectra of 9,9′-bianthryl (BA) and 9-phenyl-anthracene ( 9PA ) were studied in 2-methylbutane ( 2 MB ) at various temperatures in the range 110–298 K and in 2MB/benzene (BE) solvent mixtures at 298 K. Effective S1 torsional potentials of BA and 9PA in the different solvents were determined by means of a simultaneous Franck-Condon and bandshape analysis of the experimental spectra. The solvent influence on the excited state torsional potential is observed to be stronger in the case of BA as compared to 9PA. The model calculations suggest that the barrier of the S~ double minimum potential of BA is increased from280 cm−1 in 2MB to465 cm−1 in BE solution whilst the minimum angle min is shifted from 62° to 58°.

Dipole moments of aminophthalimides determined by modified electro-optical absorption and emission measurements

Modified electro-optical absorption and emission methods were used to measure the electric dipole moments of five aminophthalimides in their ground and excited states. The equilibrated ground and excited state dipole moments measured by these methods are in reasonable agreement with those derived from other measurement techniques, confirming the general validity of these methods. A difference is observed between the properties of 3-aminophthalimide (3AP) and 4-amino-N-methylphthalimide (4ANMP) in different solvents. The equilibrated dipole moment of 3AP in its excited state is practically independent of the solvent polarity in contrast with 4ANMP. The possible mechanism of this effect is discussed.

Electric field-induced anisotropy spectra

Abstract A novel method for the representation of results from the measurement of the effect of an external electric field on the absorption or fluorescence of solute molecules is derived from Liptays formalism so that the pure field-induced anisotropy of the absorbance or fluorescence intensity of solute compounds can be represented over the respective wavenumber interval. The method is demonstrated with 4-N,N-dimethylamino-4′-nitrostilbene and applied to three derivatives of dimethylaminobenzonitrile, namely 1-methyl-5-cyanoindoline, 2,6,N,N-tetra-methyl-4-cyanoaniline, and 6-cyanobenzo-quinuclidine.

Model Substances for Electro-optical and Dielectric Studies, Part I Synthesis and Structure of 1,4-Bis(4'-dimethylamino-3',5'-dicyanophenyl)bicyclo[2.2.2]octane

A synthesis for a new 1,2,6-donor-acceptor-substituted chromophoric benzene system is given. This chromophore is incorporated in a bicyclo[2.2.2]octane system to build up model compounds for electro-optical and dielectrical studies. Furthermore a preparative convenient route to derivatives of 1,4-bis(diphenyl)bicyclo[2.2.2]octane is worked out. The structures of the new compounds are proven by spectroscopical means.

Substituent-induced coupling of the two lowest excited singlet states of 2-methoxy-derivatives of 4-(N,N-dimethylamino)- and 4-(N-methylamino)benzonitrile

The title compounds both exhibit strong features of interaction of their two lowest excited states, but only one of them, the dimethylamino derivative, exhibits dual fluorescence. This is a direct indication that state interaction and dual fluorescence are not directly related.