Diphenyl-polyene

Charge transfer during diphenyl-polyene sorption in acidic ZSM-5 zeolite a primordial reaction for catalysis processes... 

The mere exposure of diphenyl-polyenes (DPP) to medium pore acidic ZSM-5 was found to induce spontaneous ionization with radical cation formation and subsequent charge transfer to stabilize electron-hole pair. Diffuse reflectance UV-visible absorption and EPR spectroscopies provide evidence of the sorption process and point out charge separation with ultra stable electron hole pair formation. The tight fit between DPP and zeolite pore size combined with efficient polarizing effect of proton and aluminium electron trapping sites appear to be the most important factors responsible for the stabilization of charge separated state that hinder efficiently the charge recombination. 

Keywords ZSM-5, diphenyl polyene, ionization, charge separation, spectroscopy. 

By using the extinction coefficient of the diphenyl polyenes, we can estimate the concentration of these groups of conjugated double bonds to be between 10 and 25... 

Similar studies in zeolites having different sizes of channels/cages also reveal the importance of the directionality of free volume within the reaction cavity [159]. Both the photochemical and the photophysical behavior of trans-stilbene and longer all trans-a,w-diphenyl polyenes critically depend on the zeolite in which they are included. In pentasil zeolites (ZSM-5, -8, and... 

Aluminum, sodium, calcium and rubidium on a diphenyl-polyene... 

Wavelength Al rption of Dimethyl and Diphenyl Polyenes (Adapted from Murrell, 1963)... 

The absorption bands or peaks reported for the dl -trans conformers of unsubstituted polyenes a,m-dunethylpolyenes , a,cD-di-ferf-butylpolyenes, a,cD-diphenyl-polyenes and a,m-dithienylpolyenes are complied in Tables 1-5, respectively. The data for carotenoids are described in a previous review. These absorptions are attributed to the 1 Ag transitions (tt-tt transitions). 

Figure 2. VEH computed ionization potentials for polyenes (solid line) and diphenylpolyenes (open circles) compared to experimental data(X) from reference 30. Diphenyl-polyene results, data, theory, and experiment are plotted with n defined as in Figure 1.

Fig. 11. Predicted electronic spectra of odd polyenes 2T—32 and odd a,

The results on DP7 and DP6 are fully consistent with the results of the study of the p-doping of P-carotene, which contains a conjugated sequence of 11 double bonds. ESR measurements indicate the formation of pairs of spinless confined solitons in the -carotene di-ion [16]. Optical absorption data, however, indicate only a single in-gap absorption, because of selection rules (symmetry) in the short polyenes [16]. Optical absorption studies of the sodium-doped diphenyl-polyenes is under way. 

Diphenylpolyenes have higher oxidation potentials than polyacetylene, which can be oxidized by I2. However, Spangler and co-workers found that diphenyl polyenes from = 4-8 can be oxidatively doped in CH2CI2 solution with either FeCl3 or SbCls [26-28]. In all cases an immediate bleaching of the original n—n transition was observed with the simultaneous appearance of new red-shifted bands which for the longer polyenes may be into the near infrared (NIR). In some... 

Table 9.4. Bipolaron formation in dianthracenyl polyenes compared to equivalent diphenyl polyenes...

Scheme 1 D-A pairing for a typical D,A-substituted diphenyl polyene.

C, W. Spangler, K. O. Havelka, M. W. Becker, T. A. Kelleher, and L.-T. Cheng, Relationship between conjugation length and third-order nonlinearity in bis-donor substituted diphenyl polyenes, Proc. SPIE /5d0 139 (1991). 

J. R. Tallent, R. R. Birge, C. W. Spangler, and K. O. Havelka, Theoretical analysis of third order polarizability enhancement of disubstituted diphenyl polyenes via oxidative doping, in Molecular Electronics—Science and Technology (A. Aviram, ed.). Am. Inst. Phys., New York. 1992, pp. 191-203. 

---