Matrix isolation fluorescence

The theory of rotation effects on prolate luminescent molecules in solution and its experimental verification have been developed and compared. Generalized diffusion equations for the rotational motion of an asymmetric rigid motor have been used to given an expression for steady-state fluorescence depolarization. " The radiationless transition from the first excited singlet state of Eosin has been measured by optoacoustic relaxation, and the absolute fluorescence quantum yields of organic dyes in poly(vinyl alcohol) have also been measured by the photoacoustic method. The accuracy of the method has been discussed in the latter paper. Actinometry in flash photolysis experiments has been assisted by new measurements on the extinction coefficient of triplet benzophenone. Matrix-isolation fluorescence spectrometry has been used to detect polycyclic aromatic hydrocarbons from gas chromatography. ... 

Techniques other than UV-visible spectroscopy have been used in matrix-isolation studies of Ag see, for example, some early ESR studies by Kasai and McLeod 56). The fluorescence spectra of Ag atoms isolated in noble-gas matrices have been recorded (76,147), and found to show large Stokes shifts when optically excited via a Si j — atomic transition which is threefold split in the matrix by spin-orbit and vibronic interactions. The large Stokes shifts may be explained in terms of an excited state silver atom-matrix cage complex in this... 

Raman spectra of S2 in its triplet ground state have been recorded both in sulfur vapor and after matrix isolation using various noble gases. The stretching mode was observed at 715 cm in the gas phase [46], and at 716 cm in an argon matrix [71]. From UV absorption and fluorescence spectra of sulfur vapor the harmonic fundamental mode of the S2 ground state was derived as t e = 726 cm . The value corrected for anharmonicity is 720 cm [26, 27]. Earlier reports on the infrared absorption spectrum of 2 in matrix isolated sulfur vapor [72] are in error the observed bands at 660, 668 and 680 cm are due to S4 [17] and other species [73]. 

Figure 4.3 shows the fluorescence SNOM images of single PMMA-Pe chains embedded in the unlabeled PMMA matrix. In the SNOM image, each PMMA-Pe chain was observed as an isolated fluorescent spot. The molecular weight of each chain can be estimated from the integrated fluorescence intensity [19], and Figure 4.3... 

Stereochemistry. - There has been a far infra-red spectroscopic study of ethyl phosphine,130 and in combination with X-ray fluorescence, further work completed on the conformational analysis of dialkylphenyl phosphines.131 The influence of water on the conformational equilibria of trimethyl phosphate has received attention.132 There has been a low temperature solid state and matrix isolation study of methyl phosphorodichi oridate,133 and a conformational study of polymorphic modifications of diphenyl-phosphinyl acetic acid hydrazide. 34... 

Conventional EPR techniques have been successfully used to measure the D and E values of matrix-isolated carbenes in the ground triplet state because the steady-state concentration of triplet species is sufficiently high in the system. The technique cannot be used, however, for excited species having triplet hfetimes of the order of 10-100 ns, since their steady-state concentration is too low. The D parameters are estimated from the external magnetic field effect on the T—T fluorescence decay in a hydrocarbon matrix at low temperamre. The method is based on the effect of the Zeeman mixing on the radiative and nonradiative decay rates of the T -Tq transition in the presence of a weak field. The D values are estimated by fitting the decay curve with that calculated for different D values. The D T ) values estimated for nonplanar DPC (ci symmetry) is 0.20... 

Figure 8. Far-infrared emission measurements of H02 of Traub et al (85) ( ), millimeter-wave emission measurements of de Zafra et al. (86) ( + ), resonance fluorescence measurements of Anderson et al. (107) (A), and matrix isolation-EPR measurements of Helten et al. (96) (O). (Reproduced with permission from reference 85. Copyright 1990 American Association for the Advancement...

At low enough temperatures vibrational fine structure of aromatic chromophores may be well resolved, especially if they are embedded in a suitable matrix such as argon or N2, which is deposited on a transparent surface at 15 K. This matrix isolation spectroscopy77166 may reveal differences in spectra of conformers or, as in Fig. 23-16, of tautomers. In the latter example the IR spectra of the well-known amino-oxo and amino-hydroxy tautomers of cytosine can both be seen in the matrix isolation IR spectrum. Figure 23-16 is an IR spectrum, but at low temperatures electronic absorption spectra may display sharp vibrational structure. For example, aromatic hydrocarbons dissolved in n-heptane or n-octane and frozen often have absorption spectra, and therefore fluorescence excitation spectra, which often consist of very narrow lines. A laser can be tuned to excite only one line in the absorption spectrum. For example, in the spectrum of the carcinogen ll-methylbenz(a)anthrene in frozen octane three major transitions arise because there are three different environments for the molecule. Excitation of these lines separately yields distinctly different emission spectra.77 Likewise, in complex mixtures of different hydrocarbons emission can be excited from each one at will and can be used for estimation of amounts. Other related methods of energy-... 

The different techniques of flash photolysis are used to detect transient species, that is atoms, molecules and fragments of molecules which have very short lifetimes. These cannot be observed by usual experimental techniques which require rather long observation times. For example, the measurement of an absorption or fluorescence spectrum takes several seconds, and this is of course far too long in the case of transient species which exist only for fractions of a second. In some cases these transient species can be stabilized through inclusion in low-temperature rigid matrices, a process known as matrix isolation . 

The silylene center does not react with ethylene. In this respect it is similar to CI2Si , which reacts with ethylene at a significant rate only at high temperatures (793 K). Ethylene, however, quenches the silylene fluorescence, as does CO348. In both cases a charge-transfer complex may be involved. (CO forms weak complexes with matrix-isolated silylenes see Section V.A.2)... 

Figure 6.8. Fluorescence excitation spectra of matrix isolated 9-deuteroxyphenalenone (lower) and methyl-9-deuteroxyphenalenone (upper) as examples of nearly symmetric and asymmetric double well potentials for hydrogen transfer, shown on the left. The suppression of hot band 01 is shown in a separate spectrum at 3.5 K. Due to asymmetry of the potential, the wave functions are linear combinations of the left and right well function with different amplitudes if/t = a2 + b2, ij/a = -b2 + a2, b/a = 0.22 and 0.80 in the ground and excited states of the methyl derivative. (From Barbara et al. [1989].)...

In the technique of matrix isolation (hereafter denoted "MI"), samples which are liquid or solid at room temperature are vaporized under vacuum, and then mixed with a large excess of a diluent gas (termed the "matrix gas") which in effect, is the "solvent" in the spectroscopic analysis. This gaseous mixture is then deposited on a cold surface for spectroscopic analysis as a solid For most purposes, temperatures of 15 K (which can be obtained by use of commercial closed-cycle refrigerators) are satisfactory for some specialized fluorescence experiments,... 

The technique of matrix isolation has been shown to produce highly characteristic spectra of individual components of complex samples combination of MI spectroscopy with separation techniques promises to increase further the analytical capabilities of the technique. While our research to date has emphasized FTIR and molecular fluorescence spectrometry, MI as a sampling procedure is not limited to these two forms of spectrometry. For example, some interesting preliminary analytical results by MI Raman spectrometry recently have been described (32). It should also be stressed that the cryogenic procedures required for the vast majority of MI spectral studies are neither difficult nor unduly expensive except in very special cases, closed-cycle cryostats requiring no cryogenic liquids (and no prior experience in low-temperature techniques) are entirely satisfactory for MI... 

The approach to low-temperature spectroscopy that we have chosen to pursue is termed matrix isolation (MI). In MI, the sample is vaporized and then mixed with a large excess of a diluent gas (18,19,20), The gaseous mixture then is deposited on a window at low temperature for spectroscopic examination. The purpose of mixing the sample with the solvent (matrix gas) in the vapor phase is to secure an essentially random distribution of solute molecules, such that each analyte molecule has only matrix gas molecules as nearest neighbors. If this objective is achieved, and if the dilution is sufficiently great that the average distance between any two solute molecules is sufficiently large, then the fluorescence of any one analyte in a complex sample should be essentially unperturbed by the... 

Azulene is one of the most interesting molecules from the photophysical point of view. A picosecond measurement of the vibrational energy decay in matrix isolated polyatomic molecules shows at 4K that molecular modes in a polyatomic matrix does not affect decay in the 2 vibrational manifold . The S2 Sq fluorescence of pseudoazulenes has been studies in Shpolski... 

Shirk, J. S., and Bass, A. M., Laser-excited fluorescence of matrix-isolated molecules. Anal. Chem. 41, 103A (1969). 

Diatomic cations, neutral molecules, and anions represent the type of inorganic species which has been most extensively studied by resonance Raman spectroscopy. Iodine in the gaseous, dissolved, and matrix-isolated states has been the subject of particularly detailed studies, and it is this molecule for which the greatest number of members (25) of a resonance Raman progression has so far been observed (66). The relation between resonance Raman and resonance fluorescence spectra has been discussed in Section 2, but it is worth illustrating the general principles involved by reference to the work on iodine. 

Fakhruddin, A., Fluorescence spectra of matrix-isolated BiS, BiSe, and BiTe, J. Chem. Phys., 82, (1985), 4401-4404. Cited on page 198. 

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