Low-lying Lowest Unoccupied Molecular Orbital Research Articles

Air-Stable n-Type Organic Field-Effect Transistors Based on 4,9-Dihydro-s-indaceno[1,2-b:5,6-b′]dithiazole-4,9-dione Unit

4,9-Dihydro-s-indaceno[1,2-b:5,6-b′]dithiazole-4,9-dione (IDD) was designed as a novel electronegative unit, and the π-conjugated compound (2C-TzPhTz) containing it was synthesized as a candidate for air-stable n-type organic field-effect transistor (OFET) materials. Cyclic voltammetry measurements revealed that the IDD unit contributes to lowering the lowest unoccupied molecular orbital (LUMO) energy level. X-ray crystallographic analysis of 2C-TzPhTz showed an almost planar molecular geometry and dense molecular packing, which is advantageous to electron transport. OFETs based on 2C-TzPhTz showed high electron mobility of up to 0.39 cm2 V–1 s–1, which is one of the highest electron mobilities observed among pentacyclic dione-based materials. Top-contact OFET devices showed operating stability and long-term stability under ambient conditions, attributed to the low-lying LUMO energy level and dense packing in the solid state. Furthermore, bottom-contact OFETs also maintained good electron mobility beyond ...

A host material with a small singlet–triplet exchange energy for phosphorescent organic light-emitting diodes: Guest, host, and exciplex emission

A host material containing a triazine core and three phenylcarbazole arms, called 2,4,6-tris(3-(carbazol-9-yl)phenyl)-triazine (TCPZ), was developed for phosphorescent organic light-emitting diodes (OLEDs). Ultra-low driving voltages were achieved by utilizing TCPZ as the host due to its decreased singlet–triplet exchange energy (ΔEST) and low-lying lowest unoccupied molecular orbital (LUMO) energy level. Interaction between the RGB triplet emitters and TCPZ were studied in both photoluminescent and electroluminescent processes. Transient photoluminescence (PL) measurement of the co-deposited film of fac-tris(2-phenylpyridine) iridium (Ir(PPy)3):TCPZ exhibits a shoulder at 565nm whose lifetime is about two times longer than that of the Ir(PPy)3 triplet excitons and can be attributed to the triplet exciplex formed between Ir(PPy)3 and TCPZ. Such exciplex was also found for the green phosphorescent OLED, giving the most efficient phosphorescent OLED with triplet exciplex emission hitherto. Different from the PL process, a broad featureless band with a maximum at 535nm was found for the OLED based on an EML of iridium(III) bis(4,6-(di-fluorophenyl)pyridinato-N,C2′)picolinate (FIrpic):TCPZ, which can be attributed to the emission from the singlet excited state of TCPZ formed by direct hole-electron recombination. A multi-emitting-layer white OLED was also fabricated by utilizing FIrpic and tris(1-phenylisoquinolinolato-C2,N)iridium(III) (Ir(piq)3) as the complementary triplet emitters and TCPZ as the host. Different from most of ever reported white OLEDs fabricated with blue/red complementary triplet emitters that exhibit color rendering index (CRI) lower than 70, a high CRI of 82 is achieved due to the combination of blue and red phosphorescence emissions from FIrpic and Ir(piq)3, and the emerging green fluorescence emission from TCPZ.

Sensitive detection of hazardous explosives via highly fluorescent crystalline porous aromatic frameworks

A three-dimensional (3D) porous aromatic framework (PAF-14) with high fluorescence quantum yield was synthesized from luminescent monomer of tetra(4-dihydroxyborylphenyl)germanium (TBPGe) building blocks. The powder X-ray diffraction (PXRD) analysis of the experimental and simulated patterns indicate that PAF-14 is highly crystalline with ctn topology. The Argon sorption measurement indicates that PAF-14 possesses high surface area (Brunauer Emmet Teller surface area: 1288 m2 g−1). Significantly, the introduction of germanium into PAF-14 skeletons may bring about a low-lying lowest unoccupied molecular orbital (LUMO) and the crystalline polymeric backbones enhance the sensitivity of electron delocalization. Therefore the designed PAF-14 exhibits high fluorescence quenching ability for hazardous explosives, such as nitrobenzene, 2,4-DNT (2,4-dinitrotoluene) and TNT (2,4,6-trinitrotoluene).

Air‐Stable n‐Type Organic Field‐Effect Transistors Based on Solution‐Processable, Electronegative Oligomers Containing Dicyanomethylene‐Substituted Cyclopenta[b]thiophene

Solution-processable, electronegative, π-conjugated systems containing dicyanomethylene-substituted cyclopenta[b]thiophene were synthesized as potential active materials for air-stable n-type organic field-effect transistors (OFETs). Electrochemical measurements revealed that these compounds exhibited electrochemical stability and that the lowest unoccupied molecular orbital (LUMO) had an energy level less than -4.0 eV. Flash-photolysis time-resolved microwave conductivity (FP-TRMC) measurements were performed, and the value of intradomain electron mobility was determined to be as high as 0.1 cm(2) V(-1) s(-1) . The OFETs were fabricated by spin-coating thin films of the compounds as an active layer. The electron mobility of the OFETs was 3.5×10(-3) cm(2) V(-1) s(-1) in vacuum. Furthermore, electron mobility of the same order of magnitude and stable characteristics were obtained under air-exposed conditions. X-ray diffraction measurements of the spin-coated thin films revealed the difference of molecular arrangements depending on the inner conjugated units. Atomic force microscopy measurements of crystalline-structured films exhibited the formation of grains. The accomplishment of air-stability was attributed to the combined effect of the low-lying LUMO energy level and the molecular arrangements in the solid state, avoiding both the quenching of electron carriers and the intrusion of oxygen and/or moisture.

Electron rectification through donor-acceptor-heterocyclics connected to cumulenic bridge: a computational study

Abstract Density Functional Theory (DFT) calculations and Frontier Molecular Orbital (FMO) analysis have been carried out at B3LYP/6-31G(d,p) level of theory on some Donor-Bridge-Acceptor (D-B-A) molecules for their electrical rectification behavior. The donor-acceptor-heterocyclics (D/A-heterocyclics) (namely thiophene, furan and pyrrole rings) are attached as donor and acceptors to the two ends of cumulenic bridge. FMO analysis indicates that the molecules having even number of double bonds in the bridge, possess a complete localization of the MOs i.e., the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) are localized on the donor and the acceptor side of the molecules respectively, and LUMO+1 is localized on the donor side, where as in case of odd number of double bonds in the bridge, both the HOMO and LUMOs are delocalized all over the molecule. The Potential Drop (PD) in the former case decreases as the number of double bonds increases in the bridge and due to the presence of the mutually orthogonal and noninteracting π-clouds, they can act as molecular rectifiers. For the molecules with the odd number of double bonds due to the low-lying LUMO delocalized all over the molecule, may find application as molecular wires in molecular electronics circuits.

Radikaltrianionen von Isopyrenen

Radical Trianions of IsopyrenesThe radical trianions derived from acepleiadylene (1), dicyclopenta [ef,kl]heptalene (2) and dicyclohepta [cd, gh]‐pentalene (3) are described. Whereas the hyperfine data of \documentclass{article}\pagestyle{empty}\begin{document}$ 1^{3\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ 2^{3\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document} are consistent with the predictions of an HMO‐McLachlan‐procedure, the corresponding data of \documentclass{article}\pagestyle{empty}\begin{document}$ 3^{3\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document} substantially differ from the calculated values. The spin distribution in \documentclass{article}\pagestyle{empty}\begin{document}$ 3^{3\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document} is polarized by the counterions in such a way, that the hyperfine data of this radical trianion no longer reflect the D2h‐symmetry of the neutral compound 3 and the radical anion \documentclass{article}\pagestyle{empty}\begin{document}$ 3^{\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document}. In addition, the interaction of the charged organic ion \documentclass{article}\pagestyle{empty}\begin{document}$ 3^{3\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document} with the counterions influences the energy of the low‐lying antibonding molecular orbitals LUMO (lowest unoccupied molecular orbital) and NLUMO (next lowest unoccupied molecular orbital). The passage from a looser ion pair (\documentclass{article}\pagestyle{empty}\begin{document}$ 3^{3\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document}/3Li+) to a tighter ion pair (\documentclass{article}\pagestyle{empty}\begin{document}$ 3^{3\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document}/3Na+, \documentclass{article}\pagestyle{empty}\begin{document}$ 3^{3\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document}/3K+) causes a change in the orbital sequence of LUMO and NLUMO.

An application of molecular orbital theory for screening research of antifungal drugs.

The relationship between antifungal activity and the energy of the lowest unoccupied molecular orbital (LUMO) of several phenolic compounds was examined using MINDO/3 method. Among the phenols examined, all the compounds which are highly active in inhibiting the growth of fungi possess a low-lying LUMO as compared with the compounds poor in antifungal activity. From these results, it is conceivable that the LUMO energy of a molecule should be one of the useful indices for screening antifungal drugs.