Georg W. Suter

Hole burning in the absorption spectrum of chlorin in polymer films: stark effect and temperature dependence

Abstract Optical hole-burning experiments at 2 K with chlorin in polymethylmethacrylate (PMMA), polystyrene (PST) and polyvinylbutanal (PVB) gave hole widths of 1.2, 1.6 and 0.75 GHz. Preliminary temperature-dependent measurements in PVB suggest that the linewidth at 0 K approximates the lifetime-limited value. Due to the Stark effect on the randomly distributed molecules, a significant reversible broadening was observed when an electric field of 6000 V/cm was applied to the sample.

A kinetic model for the energy transfer in phycobilisomes.

A kinetic model for the energy transfer in phycobilisome (PBS) rods of Synechococcus 6301 is presented, based on a set of experimental parameters from picosecond studies. It is shown that the enormous complexity of the kinetic system formed by 400-500 chromophores can be greatly simplified by using symmetry arguments. According to the model the transfer along the phycocyanin rods has to be taken into account in both directions, i.e., back and forth along the rods. The corresponding forward rate constants for single step energy transfer between trimeric disks are predicted to be 100-300 ns(-1). The model that best fits the experimental data is an asymmetric random walk along the rods with overall exciton kinetics that is essentially trap-limited. The transfer process from the sensitizing to the fluorescing C-PC phycocyanin chromophores (tau approximately 10 ps) is localized in the hexamers. The transfer from the innermost phycocyanin trimer to the core is calculated to be in the range 36-44 ns(-1). These parameters lead to calculated overall rod-core transfer times of 102 and 124 ps for rods containing three and four hexamers, respectively. The model calculations confirm the previously suggested hypothesis that the energy transfer from the rods to the core is essentially described by one dominant exponential function. Extension of the model to heterogeneous PBS rods, i.e., PBS containing also phycoerythrin, is straightforward.

Phosphorescence line narrowing of 1-indanones upon S1 ← SO excitation

Abstract Phosphorescence line narrowing is reported for several 1-indanone derivatives upon excitation into the first singlet state. This effect observed for the first time requires a rigid link between the phenyl- and the keto-group and is ascribed to a strong correlation between the absolute state energies of S 1 (nπ*) and T 1 (nπ*) in the glassy matrix.

The structure of low-temperature electronic spectra of benzo[a]phenazine

Abstract A vibrational analysis of the multi-site phosphorescence spectra of benzo[a]phenazine (BPH) in n-hexane and of the single-site phosphorescence spectra obtained by direct T1(π,π*)←So laser excitation in a glassy medium furnished consistent results. Using polarization spectra, the symmetries of fundamentals active in the phosphorescence spectra have been assigned. The BPH molecule occupies in a n-hexane matrix three main sites. The site splitting is much larger in the T1 than in the S1 state. The energy gap between the S2(ππ*) and the S1(nπ*) state is only 650 cm−1. In the interference region between these two slates large intensity differences in the phosphorescence excitation spectra of the individual sites are observed.

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.

Energy selection experiments: The total phosphorescence spectrum of 1,4-diazatriphenylene

Abstract The phosphorescence spectra of 1,4-diazatriphenylene in isopentane- and 3-methylpentane-glasses and in a n -hexane Shpolskii matrix depend on the excitation wavelength. The total phosphorescence spectra are presented and discussed in terms of a model using different distribution functions for the inhomogeneous broadening of the electronic states S 0 , S 1 and T 1 .

Energy selection spectroscopy in the triplet state: High resolution phosphorescence polarization spectra of benzo[a]phenazine

Abstract The technique of energy selection utilizing direct T 1 ←S 0 excitation was used to obtain highly resolved phosphorescence spectra of benzo[a]phenazine in glassy matrices at 2–4K. In a heavy atom solvent a specific enhancement of the totally symmetric vibrational bands was found. For the first time highly resolved spectra of the degree of phosphorescence polarization were obtained, using a combination of the energy selection and the photoselection techniques.

The dual phosphorescence of benzophenazine in ethanol

Abstract Using the technique of two-dimensional luminescence spectroscopy, a strong excitation dependence of the phosphorescence spectrum of benzo[a]phenazine (BPH) in glassy ethanol has been discovered. It was found that all phosphorescence spectra 5obtained by excitation at any wavelength may be understood as a superposition of two subspectra A and B having the same vibrational structure: I(ovbar|ν) = aA(ovbar|ν)+ bB (ovbar|ν), with A(ovbar|ν) = B(ovbar|ν - Δ \ gn). In ethanol these subspectra are shifted relative to each other by 225 cm−1. Their excitation spectra have the same shape with a relative displacement of 460 cm−1. The results obtained in different solvents and solvent mixtures allow the two subspectra to be assigned to the free and the H-bonded form of BPH. The appearance of different species is also observed in the phosphorescence spectra of some other para-diazines in protic solvents.

The structure of low-temperature electronic spectra of benzo[a]phenazine II. Phosphorescence excitation spectra in n-hexane and n-octane matric

Abstract The line pattern of the phosphorescence excitation spectra of benzo[a]phenazine (BPH) in n -hexane and n -octane at 4 K are strongly site depende

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.