ABSTRACT
Organic diradicaloids have lately emerged as potential spintronic materials. We report the unprecedented synthesis of a near-IR absorbing indeno[2,1-a]fluorene derivative that displays remarkably low LUMO (-4.15 eV) and a small HOMO-LUMO gap (0.85 eV). NMR/EPR studies indicated its open-shell diradical property, which was supported by DFT calculations while suggesting a 30% diradical character and a small singlet (S)-triplet (T) gap (-2.52 kcal mol-1). A large bond length alternation of the as-indacene core for its single-crystals indicated a quinoidal contribution with greater antiaromaticity, which is in line with the small diradical character despite showing a small S-T gap.
ABSTRACT
A thiophenoradialene-embedded polycyclic heteroterphenoquinone (PHTPQ) derivative of diindeno[1,2-b:2',1'-d]thiophene-2,8-dione, with antiaromatic characteristics, was synthesized by dehydrogenating its fluorescent dihydro PHTPQ precursor. The antiaromatic character was evidenced by the visible absorption band with a weakly intense tail extending to 800 nm in the near-infrared region (forbidden HOMO â LUMO transition) and non-emissive and amphoteric redox properties. Single-crystal and (anti)aromaticity analyses found a non-aromatic thiophene core while suggesting antiaromaticity/paratropicity of the pentafulvene subunits dominating the overall ground state properties.
Subject(s)
Coloring Agents , ThiophenesABSTRACT
peri-Acenoacenes are attractive synthetic targets, but their non-benzenoid isomeric counterparts were unnoticed. 1-Ethoxyphenanthro[9,10-e]acephenanthrylene 8 was synthesized and converted to azulene-embedded 9, which is a tribenzo-fused non-alternant isomeric motif of peri-anthracenoanthracene. Aromaticity and single-crystal analyses suggested a formal azulene core for 9, which showed a smaller highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) energy gap with a charge-transfer absorption band and brighter fluorescence than 8 (quantum yield (Φ): 9 = 41.8%, 8 = 8.9%). The reduction potentials of 8 and 9 were nearly identical, and the observations were further supported by density functional theory (DFT) calculations.
ABSTRACT
Dicyclopenta[c]fluorenothiophene 5 was synthesized as the isoelectronic polycyclic heteroarene analogue of an as-indacenodifluorene with a (4n + 2)π-electron perimeter. Single-crystal and 1H NMR analyses indicated a quinoidal ground state for 5, which was supported by theoretical calculations while suggesting a degree of antiaromaticity of the as-indacene subunit greater than that for s-indacenodifluorene 3. The dominant antiaromaticity for 5 was evidenced by the broad weakly intense absorption tail reaching the near-IR region, four-stage redox amphotericity, and small HOMO-LUMO energy gap.
ABSTRACT
Parent 2,3:10,11-dibenzoheptazethrene is a singlet diradicaloid polycyclic hydrocarbon in the ground state that did not change its diradical character upon substitution (methyl and triisopropylsilylethynyl). Described herein are the synthesis and characterization of an ethoxy/3,5-(CF3)2C6H3-substituted 2,3:10,11-dibenzoheptazethrene 3 that prefers to retain its p-quinoidal core and shows zero diradical character, as determined by single-crystal analysis and density functional theory calculations. Negative solvatochromism, π-π interactions, Csp2-H···O hydrogen bonding, intramolecular charge transfer, redox amphotericity, and a narrow HOMO-LUMO energy gap make 3 a potential candidate for application in optoelectronics.
ABSTRACT
Described herein is an alternative synthetic approach for conjugated indeno[2,1-c]fluorene, including the experimental and theoretical investigations of a tetraradicaloid s-indaceno[2,1-c:6,5-c']difluorene that belongs to the rarely explored indacenodifluorene family containing 4n + 2 monocyclic conjugated π-electrons. Expedient synthesis, broad absorption reaching 1150 nm, and small HOMO-LUMO energy gap make [2,1-c:6,5-c']s-IDF a promising candidate for optoelectronic applications.
ABSTRACT
Multidrug resistance (MDR) in cancer cells can significantly attenuate the response to chemotherapy and increase the likelihood of mortality. The major mechanism involved in conferring MDR is the overexpression of ATP-binding cassette (ABC) transporters, which can increase efflux of drugs from cancer cells, thereby decreasing intracellular drug concentration. Modulators of ABC transporters have the potential to augment the efficacy of anticancer drugs. This editorial highlights some major findings related to ABC transporters and current strategies to overcome MDR.
