Optoelectronic Properties of Carbon Nanorings: Excitonic Effects from Time-Dependent Density Functional Theory

The electronic structure and size-scaling of optoelectronic properties in cycloparaphenylene carbon nanorings are investigated using time-dependent density functional theory (TDDFT). The TDDFT calculations on these molecular nanostructures indicate that the lowest excitation energy surprisingly becomes larger as the carbon nanoring size is increased, in contradiction with typical quantum confinement effects. In order to understand their unusual electronic properties, I performed an extensive investigation of excitonic effects by analyzing electron-hole transition density matrices and exciton binding energies as a function of size in these nanoring systems. The transition density matrices allow a global view of electronic coherence during an electronic excitation, and the exciton binding energies give a quantitative measure of electron-hole interaction energies in the nanorings. Based on overall trends in exciton binding energies and their spatial delocalization, I find that excitonic effects play a vital role in understanding the unique photoinduced dynamics in these carbon nanoring systems.Comment: Accepted by the Journal of Physical Chemistry

MOLECULAR BELTS .2. SUBSTRATE-DIRECTED SYNTHESES OF BELT-TYPE AND CAGE-TYPE STRUCTURES

The trebly-diastereoselective synthesis and structural characterization of two macropolycyclic derivatives, which are based upon building blocks incorporating six-membered rings that are both [a,c] - and [a,d] -fused, have been achieved by a Diels-Alder oligomerization reaction sequence. The angular syn bisdienophile 3 has been used as a Diels-Alder building block with the bisdiene 12 in a trebly-diastereoselective synthesis of the angular macropolycyclic derivative 5. The incorporation of two diametrically-opposed [a,c]-fused units into the skeleton of 5 imposes a conical nature upon the cavity compared with the structures of macropolycyclic compounds such as the cyclacene derivatives 1 and 2. The construction of the angular macropolycyclic derivative 5 anticipates the use of the C3v trisdienophile 4, with the bisdiene 12, in the substrate-directed synthesis of a novel cage-like compound dubbed trinacrene 6. The structural characterization of both the angular macropolycyclic derivative 5 and trinacrene 6 has been achieved by high-field NMR spectroscopy and FABMS. In each case, the operation of treble diastereoselectivity during each cycloaddition step dictates the structures of the products, underlining the utility of these stereoregular Diels-Alder oligomerizations to control the formations of molecular structures.</p

Lignans and sesquiterpene lactones from Hypochaeris radicata subsp. neapolitana (Asteraceae, Cichorieae)

Four undescribed lignans and two undescribed sesquiterpenic acids, together with three known compounds (hypochoeroside C, hypochoeroside D, and 5-O-caffeoylshikimic acid) were isolated from the roots of Hypochaeris radicata subsp. neapolitana (Asteraceae, Cichorieae). The lignans were identified as 4-(3,4-dihydroxybenzyl)- 2-(3,4-dihydroxyphenyl)tetrahydrofuran-3-carboxy-O-β-D-glucopyranoside, 4-(3,4-dihydroxybenzyl)- 2-(3,4-dihydroxyphenyl)tetrahydrofuran-3-carboxy-O-β-D-glucopyranosyl-2′-O-methacrylate, (7S,8R,8′R)-7-(3,4-dihydroxyphenyl)-3′,4′-dihydroxy-7,8,7′,8′-tetrahydronaphtho [8,8′-c]furan-1(3H)-one, and (7S,8R,8′R)-7-(3,4-dihydroxyphenyl)-3′,4′-dihydroxy-8'-(hydroxymethyl)-7,8,7′,8′-tetrahydronaphthalen-8-carboxylic acid. The two sesquiterpenic acids were identified as the ring open precursors of hypochoerosides C and D. Structures were elucidated using NMR and HRMS. Absolute configurations of (7S,8R,8′R)-7-(3,4-dihydroxyphenyl)- 3′,4′-dihydroxy-7,8,7′,8′-tetrahydronaphtho [8,8′-c]furan-1(3H)-one and (7S,8R,8′R)-7-(3,4-dihydroxyphenyl)- 3′,4′-dihydroxy-8'-(hydroxymethyl)-7,8,7′,8′-tetrahydronaphthalen-8-carboxylic acid were determined using electronic circular dichroism (ECD) spectroscopy. 4-(3,4-dihydroxybenzyl)-2-(3,4-dihydroxyphenyl)tetrahydrofuran- 3-carboxy-O-β-D-glucopyranoside was evaluated for its anti-proliferative activity against myeloma cell lines MM1S, U266, and NCI-H929 and showed cytotoxicity at 100mM against MM1S strain. No neurotoxicity was observed for major compounds 4-(3,4-dihydroxybenzyl)-2-(3,4-dihydroxyphenyl)tetrahydrofuran- 3-carboxy-O-β-D-glucopyranoside, hypochoeroside C, and hypochoeroside D in a fluorescence assay measuring neurite outgrowth in dorsal root ganglion (DRG) neurons. Additionally, compounds 4-(3,4-dihydroxybenzyl)-2- (3,4-dihydroxyphenyl)tetrahydrofuran-3-carboxy-O-β-D-glucopyranoside, hypochoeroside C, hypochoeroside D, and hypochoerosidic acid D were quantified in unstressed and drought-stressed plants using HPLC-DAD. Drought-stressed plants were found to contain lower concentrations of the lignan 4-(3,4-dihydroxybenzyl)-2- (3,4-dihydroxyphenyl)tetrahydrofuran-3-carboxy-O-β-D-glucopyranoside and sesquiterpene lactone hypochoeroside C