Erich C. Meister

Spectral hole burning: Electric field effect on resorufin, oxazine-4 and cresylviolet in polyvinylbutyral

Abstract High resolution optical studies have been performed on the dyes resorufin, oxazine-4 and cresylviolet in polyvinylbutyral films. Spectral hole burning with holographic detection allows to probe shallow holes at low laser power. From the analysis of the spectral line shape profiles under the influence of an external electric field (Stark effect) the magnitude of the difference between the dipole moment in the ground and excised state | δμ m | = | μ ( S 1 )- μ ( S 0 )|, the angle θ between δ μ m and the transition dipole moment D , as well as matrix induced contributions | δμ ind | were derived. Homogeneous linewidths of 330, 450 and 600 MHz were obtained at 1.7 K for the three dyes resorufin, oxazine-4 and cresylviolet. Time-correlated single photon counting was used for the measurement of the fluorescence lifetimes of the three dyes in polyvinylbutyral at 77 K.

Time response of small side‐on photomultiplier tubes in time‐correlated single‐photon counting measurements

The position‐dependent time response of eight small side‐on type photomultiplier tubes (Hamamatsu R928 and R955) has been investigated. Using the method of time‐correlated single‐photon counting relative transit times, single‐photon response widths and relative quantum yields have been determined. This characterization provides the basis for the proper selection and use of fast photomultiplier tubes in single‐photon counting experiments.

Total luminescence spectra of aromatic hydrocarbons in n-alkanes: Molecules in Shpolskii-sites and in glass-like regions

Abstract The total luminescence spectroscopy (TLS) method was used to study electronic spectra of aromatic hydrocarbons in polycrystalline and glassy matrices. Characteristic patterns of zero-phonon lines with their phonon wings, single-site spectra, multiplet spectra, and strongly inhomogeneously broadened spectra are discussed in terms of discretely and continuously distributed electronic energy levels of guest molecules. An overview of different types of excitation-emission dependences is presented.

Spectroscopic evidence for the coexistence of two stereoisomers of tetrabenzonaphthalene in Shpol'skii-type matrices at 4.2 K

Abstract Highly resolved fluorescence and phosphorescence excitation and emission spectra and two-dimensional total luminescence spectra of tetrabenzonaphthalene (TBN) in the Shpolskii-type matrices n -hexane and n -heptane were measured at 4.2 K. Two different vibrational patterns could be observed in the multisite spectra under site-selective excitation and emission conditions. These patterns are attributed to two TBN stereoisomers with non-planar geometries D 2 and C 2h , occupying different sites in the polycrystalline matrices. A vibrational analysis of the most intense excitation and emission subspectra was performed, providing the fundamental frequencies of one stereoisomer in the S 0 and S 1 states. The energies of the singlet states of the TBN molecules calculated for D 2 and C 2h geometry are compared with experimental data.

Total luminescence spectroscopy

Abstract The low temperature total luminescence spectra of pyrene in a single crystal of n-heptane, in a n-heptane Shpolskii matrix and in an ethanol glass, were compared. Characteristic patterns of a single-site spectrum, a multi-site spectrum, and a strongly inhomogeneously broadened spectrum were identified.

Solid state photochemistry at 4.2 K: The photocyclization of [5] helicene to dihydrobenzoperylene in hpolskii matrices

Abstract The reversible photocyclization reaction of [5]helicene to dihydrobenzoperylene (DHBP) was studied in the Shpolskii matrices n-pentane and n-hexane at 4.2 K. The well-resolved transitions from the photochemical product are attributed to DHBP, occupying a distinct site in n-hexane. The photoinduced formation of DHBP at 4.2 K was monitored during illumination by sequentially recording fluorescence spectra. The multiplet structure of [5]helicene and DHBP in fluorescence and in phosphorescence in n-pentane were determined by high-resolution total luminescence spectroscopy (TLS). The subsequent dehydrogenation of DHBP to benzoperylene (BP), which occurs rapidly at higher temperatures in fluid media and in the presence of hydrogen acceptors, was found to be inhibited in solid matrices.

High-resolution electronic spectra of tetrahelicene and hexahelicene in low-temperature polycrystalline matrices

Abstract Highly resolved fluorescence, phosphorescence and phosphorescence excitation spectra of tetrahelicene (THL) and hexahelicene (HHL) in polycrystalline matrices were obtained at liquid helium temperature. The observed concentration effects as well as the influence of the crystallinity of the medium on the fluorescence-to-phosphorescence intensity ratios are explained assuming the presence of fluorescent but not phosphorescent preaggregates and aggregates of the helicenes in crystalline matrices. The vibronic structures of the site-selected THL phosphorescence excitation spectra point to site-dependent distortions of the THL molecules. Calculations of electronic transitions of the HHL molecule were performed with the modified Warshel-Karplus method. The activity of out-of-plane skeletal modes in S 1 ↔S 0 and T 1 →S 0 HHL spectra correlates with the calculated HHL helix pitch changes in S 1 and T 1 states, respectively.

Investigation Of Inhomogeneous Luminescence Spectra By Total

Excitation dependent emission spectra from samples containing only a single chemical species are observed quite frequently, in particular at low temperatures. This is due to inhomogeneities in the sample solutions. From the point of view of chemical analysis this effect is rather tedious, since it mimics the behaviour of a multicomponent mixture. Some of the most abundant types of excitation dependence are reviewed using Total Luminescence Spectroscopy.