Photophysical Measurements

We thank Dr. A. Khatyr and Dr. A. S. Shawkat for performing the photophysical measurements and Dr. D. Fortin for the computations on [(Cu6I6) p,-PhSCH2CsCCH2SPh ] . We are furthermore indebted to Professor C. Strohmann for the determination of numerous X-ray structures and Professor P. D. Harvey for fruitful discussions. 

The results for the monomer 9b and the dimer 9c reveal equal solvent dependence of the discussed states. However, in these two compounds no BCT is present. The heat of formation, AHf, of the CT states is increasing almost linearly from monomer to trimer. These trends prove the observations resulting from the photophysical measurements and confirm the suggested charge-transfer behavior of exTTF-oPPE -C 0- Thus, the calculations support the hypothesis that in all solvents an excitation of the triad results in the CT state, which substantiates our interpretation of the electron-transfer mechanism. 

Similar to our assays with the ZnP-oFL -C6o conjugates, we have employed a number of photophysical measurements with complementary Fc-oFL -C6o systems (n — 1, 2). Herein, the ZnP donor has been substituted by a ferrocene moiety (Fig. 9.60). In view of the the o/z go-fluorcncs in ZnP-oFL,-C60 conjugates which... 

More detailed information on the activation pathway, which distinguishes the polymeric photoinitiators from the corresponding low-molecular-weight structural models, has been obtained by photophysical measurements [22,27,28] in terms of quantum yield and average lifetime of the triplet excited state of benzophenone moieties in the above systems. However, in order to get a better comprehension of this point, it is necessary to introduce some basic concepts about the kinetic treatment of a photoinitiated chain polymerization. 

From photophysical measurements, the recommended best values for the o+ values of stannyl methyl groups are Ph3SnCH2 -0.73(2), Me3SnCH2 -0.81, and (Me3Sn)2CH -1.06.44 However, no systematic studies of chemical reactions or physical properties of organotin compounds appear to have been carried out with the aim of determining elec-... 

Mes was used to calculate the effective emitter concentration needed for quantification of 8. Meff was also taken for determination of the TP quantum yield for irradiation abs [392], The use of average molecular weights determined by chromatographic or mass spectroscopic methods would result in unreliably large photonic data because of the above-mentioned difference between Mn and Meff. Determination of Meff from photophysical measurements permits rough evaluation of nc as shown in Eq. (52) ... 

H. Petek, K. Yoshihara, Y. Fujiwara, Z. Lin, J. H. Penn, andJ. Frederick, Is the nonradiative decay of Si civ-stilbene due to the dihydrophenanthrene isomerization channel Suggestive evidence from photophysical measurements on 1,2-diphenylcycloalkenes, J. Phys. Chem. 94, 7539-7543 (1990). 

Measuring the steady state optical absorption and emission properties of any luminescent polymer is the most basic but fundamental photophysical measurement we can make. Figure 1 depicts both the absorption and emission spectra for a series of polyfluorene oligomers and poly[9,9-di- -(2-ethylhexyljfluorene] (PF2/6), along with the fully rigid ladder type MeLPPP. 

It is clear from our results that the initial excitation in solid polystyrene must be extremely mobile in contrast to the case of the polymer in solution. However, it is now clear that available experimental results do not directly examine the mobile excitation. In particular, observed "monomer-like" emission is due to a shallow trap, which vitiates a previous analysis (Id,18) that assumed it to be due to the mobile excitation. Direct determination of mobile excitation dynamics will require extension of photophysical measurements to the picosecond time regime and efforts by us to accomplish this goal are now in progress. 

An alternative approach to obtaining a photophysical measurement of viscosity that may be applied to monitoring polymer cure is to measure the polarization properties of the fluorescence of an added probe (Scarlata and Ors, 1986). This again measures a property of the molecule that depends on its rotation in the polymerizing medium. The fluorescence is excited with polarized light and the extent of depolarization of the emission will depend on... 

Optical fibres are useful accessories in a variety of photophysical measurements. The current status and prospects for their further use in chemical analysis are assessed in an article by Norris. Luminescence spectroscopy and evanescent wave devices are topics highlighted in this review. By way of example of this developing technology a device described for luminescence examination of inorganic semiconductors may be cited. 

With the aid of CIDNP spectroscopy it was shown that the primary step of these reactions is cleavage of the X—R bond, which upon direct excitation occurs both from the singlet and the triplet state. By combining the results of CIDNP experiments and photophysical measurements, rate constants of singlet and triplet reactions could be determined. In these systems, cleavage is again faster from the singlet state. 

Aromatic polyimides and polyamides exhibit outstanding thermal stability and strength, two properties responsible for the industrial importance of these materials. The macroscopic properties are controlled to a large extent by the state of aggregation of the macromolecules and their relative orientation. Photophysical measurements, aimed at detecting polarization properties and the formation of excited-state charge transfer (CT) states have proven extremely useful tools to elucidate the microstructure of these materials. 

The absorption spectra of the soluble high fulierenes [76]fullerene (C, ), [78]fullerene (C78), [82]fullerene (Cg2), [84]fullerene (Cg4), [90]fullerene (C90), and [96]fullerene (Cgg) have been reported (Fig. 16) [54-64], though the quality of the reported spectra may require further improvements. The high fullerene samples used in photophysical measurements are mixtures of isomeric species. For Cg4, the presence of two isomers and C -D2i has been proposed,... 

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