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In order to clarify possibilities to identify the β -carotene ( β -Car) radicals in secondary electron transfer (ET) reactions in the photosystem II core complex (PSIIcc), Raman intensities of all 96 β -Car cofactors in the unit cell of PSIIcc-dimer crystals as a function of polarisation and crystal orientation were simulated based on the 2.9 A resolution structure. The Raman-active symmetry A g in the C 2 h group is assigned to the β -Car modes ν 66 and ν 67 . Simulations are in agreement with experiment for off-resonant excitation at 1064 nm. Resonant measurements at 476 and 532 nm excitation can not be explained, which is attributed to mode mixing in the excited state and the existence of different spectral pools. The identity of the β -Car oxidised in secondary ET can not be resolved by Raman measurements on PSIIcc-dimer crystals. Additional simulations show that similar measurements on PSIIcc-monomer crystals could provide a possible route to solve this issue.

The knowledge of the vibrational properties is of key importance to understand their function of β-carotene molecules in the reaction centre of the light-harvesting complexes. We present polarisation-dependent Raman spectroscopy on β-carotene molecules in two different environments: first single dimeric photosystem II crystal, and second encapsulated β-carotene in single-wall carbon nanotube bundles. Both systems have nearly perpendicular or parallel orientated β-carotene molecules. We compare the dependence of their Raman spectra on the polarisation of incident and scattered light.

We have studied the resonance Raman spectra of β-carotene in solution and in protein-complexes using laser excitation at various wavelengths in the visible region. Main focus was laid on the v 1 -band, which shows an anomalous behaviour upon variation of the excitation wavelength resulting in a frequency shift of the peak maximum. This shift is due to different excitation profiles of two closely spaced modes as shown previously for β-carotene in solution. In this work, we have extended the studies to the antenna pigment in photosystems I and II (PS I and PS II).

In photosynthesis the sunlight is collected by antenna pigments and transmitted to special molecule structures called photosystem I (PS I) and photosystem II (PS II), where the energy of light is transformed into a separation of charge. In the PS II reaction centre (RC), there are two β-carotene molecules Car D1 and Car D2 , which are oriented perpendicular to each other. The role of these molecules in the photosynthesis process is still unknown. We use Raman spectroscopy to study the two β-carotenes. We present polarised Raman measurements of the β-carotene vibrational modes in single crystals of photosystem II (PS II) and discuss the possible origin of the observed polarisation dependence. These measurements are important for the basic understanding of the β-carotene vibrational properties and guide future investigations of PS II.

Tip-enhanced Raman spectroscopy (TERS) is a high sensitivity and high spatial resolution analytical technique based on the strong field enhancement provided by a sharp metallic tip. Using a commercial atomic force microscope (AFM) combined with a confocal optical setup in reflection geometry, we are targeting samples on non-transparent electrodes. The resulting design challenges with respect to quantum efficiency, optical accessibility of the tip and the optics themselves, were balanced and taken into consideration for the presented ultra-high vacuum-TERS setup. Second, we describe the development of a TERS setup at normal pressure in air, and we present the confocal Raman and TERS spectra of dye molecules and other nanostructures.

In the present work we have studied β-carotene dissolved in dichloromethane by means of resonance Raman spectroscopy. To obtain the Raman excitation profiles Raman spectra of /3-carotene have been acquired at various wavelengths throughout the visible region. It was found that the position of the prominent peak at ca. 1524 cm -1 varies with the excitation wavelength indicating the involvement of two different modes. Possible origins of the different enhancement pattern of the two modes are discussed.