- Excited-State Aromatic Interactions in the Aggregation-Induced Emission of Molecular Rotors
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Small, apolar aromatic groups, such as phenyl rings, are commonly included in the structures of fluorophores to impart hindered intramolecular rotations, leading to desirable solid-state luminescence properties. However, they are not normally considered to take part in through-space interactions that influence the fluorescent output. Here, we report on the photoluminescence properties of a series of phenyl-ring molecular rotors bearing three, five, six, and seven phenyl groups. The fluorescent emissions from two of the rotors are found to originate, not from the localized excited state as one might expect, but from unanticipated through-space aromatic-dimer states. We demonstrate that these relaxed dimer states can form as a result of intra- or intermolecular interactions across a range of environments in solution and solid samples, including conditions that promote aggregation-induced emission. Computational modeling also suggests that the formation of aromatic-dimer excited states may account for the photophysical properties of a previously reported luminogen. These results imply, therefore, that this is a general phenomenon that should be taken into account when designing and interpreting the fluorescent outputs of luminescent probes and optoelectronic devices based on fluorescent molecular rotors.
- Sturala, Jiri,Etherington, Marc K.,Bismillah, Aisha N.,Higginbotham, Heather F.,Trewby, William,Aguilar, Juan A.,Bromley, Elizabeth H. C.,Avestro, Alyssa-Jennifer,Monkman, Andrew P.,McGonigal, Paul R.
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- Triphenylcyclopropenide Anion in the Gas Phase
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The triphenylcyclopropenide anion has been generated in the gas phase, and the approximate gas phase acidity of triphenylcyclopropene is reported.The dimethylphenylcyclopropenide has been also formed, but it appears to undergo a rearrangement that is induced by the acids used to probe its base strength.
- Bartmess, John E.,Kester, John,Borden, Weston T.,Koeser, Hans Guenther
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- Silver-Catalyzed [2+1] Cyclopropenation of Alkynes with Unstable Diazoalkanes: N-Nosylhydrazones as Room-Temperature Decomposable Diazo Surrogates
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The [2+1] cycloaddition of alkynes with diazo compounds represents one of the most powerful and reliable methods for the construction of cyclopropenes. However, it remains a formidable challenge to accomplish the cyclopropenation of alkynes with non-stabilized diazoalkanes, owing to the fact that such compounds are unstable and prone to detonation. Herein, we report a general silver-catalyzed cyclopropenation reaction of alkynes with unstable diazoalkanes, by for the first time the discovery and application of N-nosylhydrazones as room-temperature decomposiable diazo surrogates. This method allows for the efficient assembly a wide variety of cyclopropene derivatives that are otherwise difficult to access by conventional methods.
- Liu, Zhaohong,Li, Qiangqiang,Liao, Peiqiu,Bi, Xihe
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p. 4756 - 4760
(2017/04/14)
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- Termodynamics and Kinetics of Carbon-Carbon Bond Formation and Heterolysis Through Reactions of Carbocations with Carbanions in Solution
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Rate data are presented for the heterolysis of carbon-carbon bonds and their formation through coordination of resonance-stabilized carbocations and carbanions in acetonitrile solution at 25 deg C.These rates were determined by NMR line broadening and by the T jump technique (in a solution containing 0.48 M supporting electrolyte).Preliminary results are given for a "master equation" to predict some heterolysis energies in solution as a complement to Benson's method for homolysis energies.The results provide for the first time an opportunity to compare the effects of structure variation on the kinetic and thermodynamic properties for such an ostensibly simple reaction in solution.All evidence so far accumulated indicates that these reactions are dominated by ion-solvation factors so that they have little bearing on the gas-phase heterolysis energies.Ionic strength effects and substituent variation suggest that charge development is about half developed at the transition state, but we argue that this cannot be translated simply into pictures of transition-state structure.The results provide a flagrant reversal of the frequently invoked "reactivity selectivity principle" since the most reactive cation is also most selective.On the basis of these results and many others which have appeared recently it may be appropriate to discard the reactivity selectivity principle as a useful principle for either prediction or interpretation.
- Arnett, Edward M.,Molter, Kent
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p. 383 - 389
(2007/10/02)
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- η3-Cyclopropenyl and η3-Oxocyclobutenyl Iron Complexes. The Crystal Structures of (η3-C3Ph3)Fe(CO)2NO and (η3-C3Ph3CO)Fe(CO)2NO
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The title compounds are formed by the reaction of Cl with Na together with low yields of C3Ph3H and 2,3-diphenyl-1-indenone.They have been characterized by their X-ray structures, IR, 1H and 13C NMR spectra.Substitution of one CO by PPh3 in (η3-C3Ph3CO)Fe(CO)2NO (2a) enhances the polarity of the keto group in the ring thus allowing alkylation with formation of the cation 4-C4Ph3OMe)Fe(CO)PPh3(NO)>+ of 7.
- Jens, Klaus-Joachim,Valeri, Thomas,Weiss, Erwin
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p. 2872 - 2880
(2007/10/02)
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- CUMULENE PHOTOCHEMISTRY: PHENYL AND HYDROGEN MIGRATION IN PHENYLALLENE PHOTOREACTIONS
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Photoreactions of tetra- and triphenylallene and 1,3,3-triphenylcyclopropane in hydrocarbon solvents are reported.Intermediacy of vinylcarbenes is supported by independent generation experiments.
- Klett, Michael W.,Johnson, Richard P.
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p. 2523 - 2526
(2007/10/02)
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