Carotene electronic structure

The conducting AFM method has revealed interesting details of the single molecule conductance of carotene molecules. The electronic properties of carotenoids are of interest since they play a role in their biological function, especially their optical properties which are a manifestation of their delocalised electron structure. The structure of the dithiolated carotenoid used in a study by Ramachandran et al. is shown in Fig. 7-21. A synthetic molecular wire 2,5-di(phenylethynyl-4 -thioacetyl)benzene, also appraised by conducting AFM is also shown in Fig. 7-21. The measured low bias resistance of the carotenoid molecule was found to be (4.9 0.2) GQ. After... 

Previously, many aspects of the electronic structure of some of the diphenylpolyenes have been studied by optical absorption spectroscopy [15]. Doping-induced optical absorption studies of p-doping of polyenes of various lengths and with various end-groups [9], and even -carotene [16], have been reported. In addition, the diphenylpolyenes with x S 6 have been studied, in the gas phase, by UPS [17], and, for x <4, the data was analysed using the CNDO/S2 model [18]. Finally, diphenylpolyenes with an odd number of carbons in the polyene part of the molecule, have been studied by Tolbert et al. [19]. 

The aim of this chapter also is the introduction of the photo physical study of model system ( 3-carotene in RTILs) mimicking very well spectroscopic data of this photosynthetic pigment in situ in the photosynthetic system Unique fluorescence properties of P-carotene in room temperature ionic liquids (RTIL) (Bialek-Bylka et al., 2007) and new (P-carotene) electronic states (3Ag- and 1B -) of both impxjrtant in photosynthesis isomers all-frans and 15-cis in ionic liquid with dimethylformamide (DMF) were found (Bialek-Bylka et al., 2008) and also a sensor detecting the methoxy group in the cation part of imidazolium ionic liquid was developed by us (Pawlak et al., 2009). In order to determine a detailed answer to the unique fluorescence properties, aroimd 100 times higher fluorescence yield of P-carotene in (ILl) (l-methyl-3-octyloxymethylimidazolium tetrafluoroborate) than in standard solvent n-hexane, the designed structures of RTILs were synthesized and carefully purified 1-methyl-3-octyloxymethylimidazolium tetrafluoroborate (ILl), l-methyl-3-... 

The orange-red /3-carotene and deep blue azulene differ in their 77-electronic structure. 

The fine structures of P-carotene and zeaxanthin are different becanse of different side groups and slightly different electronic confignrations. 

Interporphyrin photoinduced electron transfer can of course be the basis of light-driven charge separation in more complex systems. For example, triad 42 is similar in structure to dyad 1, with the addition of a carotenoid moiety, which can serve as a secondary donor as in 35 [13]. Excitation of 42 in dichloromethane with a laser pulse at 590 nm creates two porphyrin first excited singlet states, C- Pzn-Pp and C-Pzn- Pp. As with 1, both states decay at least in part by photoinduced electron transfer to give an initial C-Pzn -Pp charge-separated state. This state can recombine to the ground state, but as with the other triads discussed above, electron donation from the carotene competes with this to yield a final C +-Pzn-Pp state with an overall quantum yield of 0.32 with 590-nm excitation. The lifetime of this final state is 240 ns. 

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