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A series of 2-quinolinone-based molecular systems with three different acceptor groups and N/ O-alkylated quinolinone compounds have been synthesised in an attempt to understand their optical properties. All the compounds were characterised by 1H NMR, 13C NMR and mass analysis. Absorption measurements revealed that charge-transfer transition was observed by introducing electron-withdrawing acceptor groups. Alkylation of 2-quinolinone at the O-position thwarts the charge-transfer transitions, whereas N-alkylation retains the charge-transfer property. The presence of resonance zwitterionic forms in the unalkylated and N-alkylated quinolinone compounds play an important role in charge-transfer transition. The effects of solvents on the absorption and emission properties of these compounds were probed through Lippert Mataga and ET(30) correlation. The Stokes shifts of O-alkylated compounds were larger than those of the unalkylated and N-alkylated quinolinone compounds. The observed higher quantum yield and Stokes shift for these compounds will make them ideal fluorescent probes. Incorporation of acceptor groups and alkylation in the quinolinone moiety alters their energy levels. Good thermal stability was observed for both unalkylated and alkylated quinolinone compounds. The trends observed in the photophysical and electrochemical properties were supported by theoretical studies. The observed tunable optical properties, which were achieved through simple N- vs. O-alkylation, results in large Stokes shifts and thermal stability, which means that the 2-quinolinone-based molecular systems are expected to emerge as potential candidates for photovoltaic and biological applications. [ABSTRACT FROM AUTHOR]

A search for novel organic luminogens led us to design and synthesize some N-fused imidazole derivatives based on imidazo[1,2- a]pyridine as the core and arylamine and imidazole as the peripheral groups. The fluorophores were synthesized through a multicomponent cascade reaction (A3 coupling) of a heterocyclic azine with an aldehyde and alkyne, followed by Suzuki coupling and a multicomponent cyclization reaction. All of the compounds exhibited interesting photophysical responses, especially arylamine-containing derivatives, which displayed strong positive solvatochromism in the emission spectra that indicated a more polar excited state owing to an efficient charge migration from the donor arylamine to the imidazo[1,2- a]pyridine acceptor. The quantum yields ranged from 0.2 to 0.7 and depended on the substitution pattern, most notably that based on the donor group at the C2 position. Moreover, the influence of general and specific solvent effects on the photophysical properties of the fluorophores was discussed with four-parameter Catalán and Kamlet-Taft solvent scales. The excellent thermal, electrochemical, and morphological stability of the compounds was explored by cyclic voltammetry, thermogravimetric analysis, and AFM methods. Furthermore, to understand the structure, bonding, and band gap of the molecules, DFT calculations were performed. The performance of the electroluminescence behavior of the imidazo[1,2- a]pyridine derivative was investigated by fabricating a multilayer organic light-emitting diode with a configuration of ITO/NPB (60 nm)/EML (40 nm)/BCP (15 nm)/Alq3 (20 nm)/LiF (0.5 nm)/Al(100 nm) (ITO=indium tin oxide, EML=emissive layer, BCP=2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline, Alq3=tris(8-hydroxyquinolinato)aluminum), which exhibited white emission with a turn-on voltage of 8 V and a brightness of 22 cd m−2. [ABSTRACT FROM AUTHOR]

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Diels Alder reactivity of corannulene has been probed using density functional theory (DFT) at B3LYP/6-31G* level by employing it both as a diene and a dienophile in cycloaddition with ethylene and 1,3-butadiene as typical partners. Computations reveal that corannulene acts better as a dienophile than as a diene and as a dienophile it undergoes normal electron demand type addition with 1,3-butadiene, and as a diene corannulene undergoes inverse electron demand type addition with ethylene. When employed as a dienophile the addition takes place preferentially in the rim position than in the spoke position due to strong steric and electronic reasons. Further in the rim addition rim exo approach is favored kinetically and thermodynamically. As a diene, corannulene shows regioselectivity for rim–spoke addition over spoke–spoke addition. Concerted type cycloadditions have been studied and the reactions are seen to take place preferentially on the convex face. The effect of substituents in butadiene on the reactivity and the reaction of butadiene–pentaindenocorannulene (an extended corannulene) system has been investigated for the most favorable rim exo positions. Copyright © 2007 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Borirane undergoes ring opening reaction with NOCl and HNF2 yielding the corresponding alkenes. Ab initio and density functional investigations of this reaction with cis- and trans-2,3-dimethylboriranes reveal that these reactions take place in a single step through the formation of a prereactive complex and a transition state giving the alkene with the same stereochemistry. Calculations clearly show that the concerted cleavage of C&bond;B bonds leads to retention of stereochemistry. Further, it shows that HNF2 cleaves boriranes more efficiently than does NOCl. Intrinsic reaction coordinate analyses and bond order analysis describe the nature of the transition state very well and fix the reaction mechanism. Solvent effect calculations through PCM model, with acetonitrile and CCl4 as solvents, do not alter the gas phase results significantly. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [ABSTRACT FROM AUTHOR]

The stereochemical course of the deamination of cis‐2,3‐dimethylaziridine by nitrosyl chloride was investigated at the QCISD/6‐31G(d) level. Calculations reveal that the reaction takes place in two steps. In the first step, the reactants form a pre‐reactive complex, followed by a spiro‐type bicyclic transition state, which on dissociative cycloelimination gives the N‐nitrosoaziridine intermediate. In the second step, this intermediate undergoes cycloreversion through a slightly asynchronous concerted transition state to form an alkene with the same stereochemistry, which is in total agreement with experiment. In the whole reaction, the denitrosation step is found to be rate‐determining. For comparison, geometry optimizations and energies were also obtained at the B3LYP/6‐31G(d) level. It was found that the B3LYP energy results differed significantly from the QCISD ones. To analyze the reason for this difference, B3LYP calculations were repeated by varying the contribution of exact exchange in the Becke functional. With respect to the QCISD results, it has been shown that the functional with 0% exact exchange yields the best activation barriers, whereas the functional with 30% exact exchange is the most suitable one to carry out the complexation and reaction energy calculations. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [ABSTRACT FROM AUTHOR]