Site selection spectroscopy

Bonsma S, Purchase R, lezowski S, Gallus J, Konz F, Volker S (2005) Green and red fluorescent proteins Photo- and thermally induced dynamics probed by site-selective spectroscopy and hole burning. Chemphyschem 6 838-849... 

Site-selection spectroscopy Maximum selectivity in frozen solutions or vapor-deposited matrices is achieved by using exciting light whose bandwidth (0.01-0.1 cm-1) is less than that of the inhomogeneously broadened absorption band. Lasers are optimal in this respect. The spectral bandwidths can then be minimized by selective excitation only of those fluorophores that are located in very similar matrix sites. The temperature should be very low (5 K or less). The techniques based on this principle are called in the literature site-selection spectroscopy, fluorescence line narrowing or energy-selection spectroscopy. The solvent (3-methylpentane, ethanol-methanol mixtures, EPA (mixture of ethanol, isopentane and diethyl ether)) should form a clear glass in order to avoid distortion of the spectrum by scatter from cracks. 

Various compounds have been analyzed by site-selection spectroscopy. An interesting application is the identification of loci of damage in DNA resulting from reactions with carcinogens such as polycyclic aromatic hydrocarbons. 

SITE SELECTIVE SPECTROSCOPY AND EXCITED STATE ABSORPTION... 

Non-metallic rare-earth compounds studied under high pressure. In almost all cases the energy level shifts as a function of pressure have been determined. The second column gives details concerning the measurements and evaluations made. In particular the following abbreviations are used L Luminescence-, A Absorption-, E Excitation-, S Site-selective spectroscopy, O Other methods, EPC Electron-Phonon Coupling, Int Intensities, LT Lifetime, CFP Crystal-Field Parameters, FIP Free-Ion Parameters, IP Intrinsic Parameters, ET Energy Transfer... 

Ideally, lanthanide ions occupy site with C3V symmetry when incorporated into the GaN lattice by substituting the Ga3+. However the actual site symmetry is often found lower than C3V due to strain and defects. So far no crystal field analysis has ever been reported for lanthanide-doped III-V QDs, due to the co-existence of multi-sites which complicates the energy level structure and makes crystal field analysis difficult. Site selective spectroscopy is a very useful tool thus proposed to investigate the different crystal field environments of lanthanide ions doped in III-V QDs. 

Site selective laser spectroscopy is a very powerful tool for studying the local environments that are present in samples. We have shown that defect structures in solids are determined by its previous history and that these structures can be measured with site selective spectroscopy. There has been no application of such techniques to geologically important questions since our work has concentrated on understanding fundamental questions about solid state defect chemistry. Our work suggests though that site selective laser spectroscopy could have important application in geological studies if it were used in the hands of people with that background. 

The properties of the lowest triplet state of Pt(4,6-dFppy)(acac) in n-octane are nearly independent of the site chosen. An investigation of two other discrete sites reveals ZFS values which do not deviate significantly from the values observed for the main site. Furthermore, even different host materials do not lead to remarkable changes. Corresponding data are summarized in Table 1. For CH2C12 the splitting could be measured directly by site-selective spectroscopy of one discrete site, while for THF only a broadband spectrum was obtained. In this case, the ZFS was obtained from the temperature dependence of the thermalized emission decay time by a fit of (3) as described in Sect 3.2. 

Hole burning The photohleaching of a feature, normally a narrow range, within an inhomogeneous broader absorption or emission band. The holes are produced by the disappearance of resonantly excited molecules as a result of photophysical or photochemical processes. The resulting spectroscopic technique is site-selection spectroscopy. 

Deep Level Centers and Site-Selection Spectroscopy... 

The rapid development of lasers has led to the publication of increasing numbers of papers concerned this year with such subjects as superfluorescence and co-operative radiation processes,451 the thermodynamics of co-operative luminescence,452 saturation, collisional dephasing, and quenching of fluorescence of organic vapours in intense laser excitation studies,453 a theoretical model for fluorescence in gases subjected to continuous i.r. excitation,454 a quantum treatment of spontaneous emission from strongly driven two-level atoms,455 the development of site-selection spectroscopy,45 and measurements of relaxation times 457 using laser excitation. 

Our study represents the first example of high pressure fluorescence line narrowing spectroscopy and demonstrates the ability of site selective spectroscopy to gain new insight into the effect of pressure on local structure in amorphous... 

Personov RI (1983) Site selection spectroscopy of complex molecules in solutions and its applications. Spectroscopy and Excitation Dynamics of Condensed Molecular Systems 10 555-619. 

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