Photoelectron spectra and electronic structures of highly substituted polyenes.
The electronic structures of the a,a,w,w-tetra-t-Bu substituted conjugated polyenes have been investigated by UPS and quantum chem. calcns. The all-trans-hexatriene (1), octatetraene (2), decapentaene (3), and the tetradecaheptaene (4) have essentially planar polyene chromophores and accordingly their p MOs are spread by about 3-5 eV. On the other hand, interaction of the double bonds is limited in the moderately twisted 1,1,6,6-tetra-tert-butyl-cis-hexatriene (5) and the highly distorted cis-1,1,6,6-tetra-tert-butyl-3,4-dimethylhexatriene (6). The first UV-Vis absorption of a,a,w,w-tetra-t-butyl-polyenes with three to thirteen conjugated C=C double bonds is linearly correlated with the PM3 calcd. HOMO-LUMO energy gap.
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