Charge-transfer complexes of some linear conjugated polyenes

Abstract

On adsorption of some electron-acceptor molecules on the solid films of all-trans-beta-carotene, beta-apo-8'-carotenal, astacene and methylbixin a new absorption band appears on the longer-wavelength side of the spectrum in addition to the original bands. The position of this new band is dependent on the electron affinity (EA) of the acceptor molecules, and the intensity of this band increases with the amount of adsorbed acceptor molecules. A linear relationship between the vmax. of the new band and EA was observed. The value of the ionization potential of the polyenes estimated from such linear relationship agrees satisfactorily with the value obtained by other methods. It has been concluded that the polyenes behave as electron donor and first form molecular charge-transfer complexes (of type [polyene . I2] with iodine) with electron acceptors, these finally dissociating to yield ionic complexes (of type [polyene . I+] with iodine).

Charge-transfer spectra of ferrocene in halocarbon solvents under photoexcitation

“…Further, (2) is only an approximate one. Indeed, such a deviation of slope from unity is a general observation in these types of experiments [24][25][26] . McConnel et al 25 have mentioned that the slope may have any value between 0⋅4-1⋅0.…”

“…It has been indicated by Foster 26 that a large deviation from straight line of unit gradient in a plot like (2) can appear if the electron donor is only weakly effective. In the case of all-trans-β-carotene, the plot of CT band energy against electron affinity of some acceptor molecules was reported 24 to be linear with a slope of 0⋅44. But the ionization potential evaluated (5⋅44 eV) for all-transβ-carotene agreed 24 well with the experimental value estimated (5⋅5 eV) from photoemission threshold.…”

“…In the case of all-trans-β-carotene, the plot of CT band energy against electron affinity of some acceptor molecules was reported 24 to be linear with a slope of 0⋅44. But the ionization potential evaluated (5⋅44 eV) for all-transβ-carotene agreed 24 well with the experimental value estimated (5⋅5 eV) from photoemission threshold. Thus, the matching of the calculated ionization potential of ferrocene with experimental value is not accidental.…”

Molecular iodine/polymer complexes

“…These include conjugated and unconjugated ones and are: the natural rubber (poly(cisisoprene), polystyrene, styrene butadiene rubber, polyacetylene, polyphenylacetylene, poly(phenylene vinylene), polybutadiene, graphite, carbon nanotubes, and fullerene C 60 . Several conjugated polyenic naturally occurring molecules such βcarotene, β apo8′carotenal, astacene, methyl bixin, lycopene, lutein, retinoic acid, vitamin A acetate, zeaxanthin, and fucoxan thin, were reported to develop CTCs with molecular iodine in the solid state [267][268][269][270][271]. A remarkable finding was that these iodinetreated molecules were endowed with high electrical conductivity, and were found, therefore, appli cations in solid state batteries [25,269,270]; there was an electrical conductivity of 10 6 S·cm 1 for the iodinated mol ecules against 10 14 S·cm 1 for the virgin molecules.…”

Molecular conformation dependent emission behaviour (blue, red and white light emissions) of all-trans-β-carotene-ZnS quantum dot hybrid nanostructures

“…This molecule can readily form a charge transfer complex with iodine and HNO 3 molecules and therefore its natural absorption is photobleached. 22 There are several reports on the investigation of b-carotene, and which are mostly fundamental in nature. [23][24][25][26] Recently, this molecule was successfully introduced into carbon nanotube nanostructures and investigated for its structural stability and conformation.…”