1,2,4.5-Tetrazine. absorption spectrum

A few years ago, a powerful version of molecular optical spectroscopy with supersonic beams and jets was developed by Smalley, Wharton and Levy . Supersonic expansion of molecules in an inert carrier gas yields an ideal spectroscopic sample. As a result of the expansion, the translational temperature of the carrier gas decreases to extremely low values (below O.I K). The flow is collisionless so that even extremely unstable species survive. Special attention was paid to fluorescence excitation spectroscopy but the technique is by no means limited to this type of spectroscopy. (Because of fundamental difficulties, however, direct measurement of light absorption in molecular beams is not easy.) Cooled molecules in the beam are electronically excited with a tunable dye laser. The emitted fluorescence is detected and plotted against the wavenumber of the exciting radiation. The obtained fluorescence excitation spectrum is generally very similar to the corresponding absorption spectrum. The technique was used for analysis of the spectra of interesting vdW molecules He. .. NOj, He... Ij, X. .. tetrazine and Xj. .. tetrazine (X = He, Ar, H ) complexes . 

There is another way of measuring of an optical transition which is not based on a coherent optical effect but also employs a coherence property of the laser, namely, its monochromaticity. In the hole-burning technique, as in the OFID method, a cw dye laser is used to create a hole in the absorption spectrum. When this hole is transient, its width, being determined in the low-intensity limit by 2( 7 ) , may be probed by side-band modulation as first demonstrated by Szabo on ruby. When the hole is permanent, as is the case in photochemical hole-burning, the width may be easily measured by means of a narrow-band excitation spectrum as first performed by de Vries and Wiersma on dimethyl j-tetrazine in durene. ... 

As can be seen in Figure 14-la. the visible absorption spectrum for 1.2,4.5-ictrazine vapor shows the line structure that is due lo the numerous rotational and vibrational levels associated wiih the excited electronic states of this aromatic molecule. In the gaseous state, the individual tetrazine molecules are suflicicntly separated from one another to vibrate and rotate freely, and the many individual absorption lines appear as a rcsuli of the large number ol vibrational and rotational energy states. In the condensed slate or in solution, however, the lelrazine molecules have little freedom to rotate, so lines due to dil ferencos in rotational cnergv... 

Fig. 31. Photoaction spectrum of p-(s-tetrazine)-phthalocyaninatoiron(II), [PcFetz] (the dotted line represents the UV/VIS absorption spectrum)...

Detailed measurements of the s-tetrazine gas-phase spectrum were made. With these data, measurement of the absolute Stokes shift S(t) is possible. Because the Stokes shift is zero in the absence of solvent nuclear dynamics, the magnitude of the Stokes shift at the earliest times represents the amount of relaxation within the experimental time resolution. The steady-state absorption and fluorescence spectra were also measured to provide an independent value of the equilibrium Stokes shift S< With this data, the absolute solvation response function... 

Figure 21-14 shows visible spectra for 1,2,4,5-tetrazine that were obtained under three different conditions gas phase, liquid phase, and aqueous solution. Notice that in the gas phase, the individual tetrazine molecules are sufficiently separated from one another to vibrate and rotate freely, so many individual absorption peaks resulting from transitions among the various vibrational and rotational states appear in the spectrum. In the liquid state and in solution, however, tetrazine molecules are unable to rotate freely, so we see no fine structure in the spectrum. Furthermore, because frequent collisions and interactions between tetrazine and water molecules cause the vibrational levels to be modified energetically in an irregular way. the spectrum appears as a single broad peak. The trends shown in the spectra... 

Figure 24-14 Typical ultraviolet absorption spectra. The compound is 1,2,4,5-tetrazine. In (a), the spectrum is shown in the gas phase, where many lines due to electronic, vibrational, and rotational transitions are seen. In a nonpolar solvent (b), the electronic transitions can be observed, but the vibrational and rotational structure has been lost. In a polar solvent (c), the strong intermolecular forces have caused the electronic peaks to blend together to give only a single smooth absorption peak. (From S. F. Mason, J. Chem.

CyclopentaM-1.2.3.4-tetrazine 10a, upon treatment with HBF4, formed a ring-opened salt through protonation at N-2. The ring-opened, diazonium character of the salt was demonstrated by an intense absorption in the IR spectrum at 2185 cm <1994CB1479>. 

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