Charge transfer complexes of polyenes: spectroscopic, dark and photoconductive studies

Abstract

Formation of molecular charge transfer (CT) complexes of some polyenes with iodine has been confirmed by spectroscopic studies. The dark and photoconductive properties of these CT complexes have been investigated in a sandwich cell. Both the dark and photoconductivity increases by several orders of magnitude by complex formation. The measured thermal activation energy is identical for dark and photoconduction in the complexes. Similar photoconduction action spectra in pure and in iodine-complexed polyenes suggest the same photocarrier generation mechanism to be operative in both the cases. Spontaneous generation of carriers by CT interaction and their migration by trapping and detrapping mechanisms seems to be responsible for electrical conduction in the CT complexes.

The charge delocalised β,β-carotene dication—preparation, structure elucidation by NMR and reactions with nucleophiles

“…(15Z )-β,β-carotene (9) provided the same β,β-carotene dication (5) as β,β-carotene (1), consistent with expected isomerisation of cationic intermediates to the most stable all-trans dication configuration (5).…”

“…The dications of the C 35 model ( 11), with 9 conjugated double bonds, and the C 45 model ( 12), with 13 conjugated double bonds, were of interest concerning λ max and stability. As expected, the dications of the nonaene 11 absorbed at shorter wavelengths (793, 880 nm) and that of the tridecaene 12 at longer wavelengths (956, 1050 nm) than that of the undecaene 1 (5), which absorbed at 928 nm in CH 2 Cl 2 at Ϫ15 ЊC. Thus, the dication of the tridecaene 12, not investigated by NMR, is the carotenoid dication studied so far absorbing at the longest wavelength.…”

“…4 Doping of carotenoids in the solid phase with iodine vapour is reported to give charge transfer complexes with good conductivity properties. (5) in CDCl 3 at Ϫ20 ЊC. See http://www.rsc.org/suppdata/ob/b3/b307531a/ have been prepared.…”

“…NIR absorptions and estimated half lives for β,β-carotene dication(5) in various solvents at room temperature and at Ϫ20 ЊC.…”

On the structure of carotenoid iodine complexes

“…Several carotenoids have been used as substrates. 12,13 Doping of various carotenoids with iodine vapour, providing charge transfer complexes, [15][16][17][18] has been used in conductivity studies.…”