The spectroscopic properties and dynamics of the lowest excited singlet states of peridinin, fucoxanthin, neoxanthin, uriolide acetate, spheroidene, and spheroidenone in several different solvents have been studied by steady-state absorption and fast-transient optical spectroscopic techniques. Peridinin, fucoxanthin, uriolide acetate, and spheroidenone, which contain carbonyl functional groups in conjugation with the carbon-carbon π-electron system, display broader absorption spectral features and are affected more by the solvent environment than neoxanthin and spheroidene, which do not contain carbonyl functional groups. The possible sources of the spectral broadening are explored by examining the absorption spectra at 77 K in glassy solvents. Also, carotenoids which contain carbonyls have complex transient absorption spectra and show a pronounced dependence of the excited singlet state lifetime on the solvent environment. It is postulated that these effects are related to the presence of an intramolecular charge transfer state strongly coupled to the S 1 (2 1 A g ) excited singlet state. Structural variations in the series of carotenoids studied here make it possible to focus on the general molecular features that control the spectroscopic and dynamic properties of carotenoids.

We have designed and implemented a practical nanoelectronic interface to G-protein coupled receptors (GPCRs), a large family of membrane proteins whose roles in the detection of molecules outside eukaryotic cells make them important pharmaceutical targets. Specifically, we have coupled olfactory receptor proteins (ORs) with carbon nanotube transistors. The resulting devices transduce signals associated with odorant binding to ORs in the gas phase under ambient conditions and show responses that are in excellent agreement with results from established assays for OR–ligand binding. The work represents significant progress on a path toward a bioelectronic nose that can be directly compared to biological olfactory systems as well as a general method for the study of GPCR function in multiple domains using electronic readout.

The spectroscopic properties of open-chain, all-trans-C 30 carotenoids having seven, eight and nine π-electron conjugated carbon-carbon double bonds were studied using steady-state absorption, fluorescence, fluorescence excitation and time-resolved absorption spectroscopy. These diapocarotenes were purified by high performance liquid chromatography (HPLC) prior to the spectroscopic experiments. The fluorescence data show a systematic crossover from dominant S 1 f S 0 (2 1 A g f 1 1 A g ) emission to dominant S 2 f S 0 (1 1 B u f 1 1 A g ) with increasing extent of conjugation. The low temperatures facilitated the determination of the spectral origins of the S 1 f S 0 (2 1 A g f 1 1 A g ) emissions, which were assigned by Gaussian deconvolution of the experimental line shapes. The lifetimes of the S 1 states of the molecules were measured by transient absorption spectroscopy and were found to decrease as the conjugated chain length increases. The energy gap law for radiationless transitions is used to correlate the S 1 energies with the dynamics. These molecules provide a systematic series for understanding the structural features that control the photochemical properties of open-chain, diapocarotenoids. The implications of these results on the roles of carotenoids in photosynthetic organisms are discussed.

The xanthophylls, violaxanthin, lutein, and zeaxanthin, associated with the antenna protein assembly of Photosystem II (PS II) play roles as light-harvesting pigments and protective agents in the photosynthetic apparatus of higher plants. The dissipation of excitation energy exceeding that needed for photosynthesis is thought to be regulated by an enzymatic process known as the xanthophyll cycle where violaxanthin and zeaxanthin are reversibly interconverted, but the role of the cycle in controlling the process in vivo is not clear. The two hypotheses are (i) direct quenching of chlorophyll excited states by the xanthophylls and (ii) indirect quenching via carotenoid-mediated changes in the structure of the light-harvesting complexes. These mechanisms depend on the structures and/or energetics of the xanthophyll pigments, which have not yet been fully elucidated. In this work, fluorescence spectroscopy at 77 K has been used to determine the energies of the S 1 excited states of violaxanthin, zeaxanthin, and the major xanthophyll component of green plants, lutein. High performance liquid chromatography (HPLC) was carried out just prior to the spectroscopic experiments to obtain isomerically pure samples devoid of fluorescent contaminants. The experiments at cryogenic temperatures provide enhanced resolution compared to room-temperature studies, reveal clearly the vibronic features of the fluorescence line shapes, and allow precise, direct assignments of the spectral origins and electronic-state energies of the molecules. The results are important for broadening our understanding of the mechanisms of light-harvesting and nonphotochemical dissipation of excess energy in plants.