Nitropyrene Photoprobes: Making Them, and What Are They Good for?

Espinoza, Eli M.; Xia, Bing; Darabedian, Narek; Larsen, Jillian M.; Nuñez, Vicente; Bao, Duoduo; Mac, Jenny T.; Botero, Fabian; Wurch, Michelle; Zhou, Feimeng; Vullev, Valentine I.

doi:10.1002/ejoc.201501339

Cited by 23 publications

(29 citation statements)

References 156 publications

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“…The sharp bands, which decay on the nanosecond timescale, are ascribed to the CT states of butterfly‐shaped heterocycles 6 a – c . Sharp TA bands are common for the spectra of radical ions of polyaromatic conjugates . Concurrently, broad and featureless spectral bands are typical for fluorescence from CT states comprised of such radicals and radical ions .…”

Section: Resultsmentioning

confidence: 98%

Nonplanar Butterfly‐Shaped π‐Expanded Pyrrolopyrroles

Krzeszewski

Kodama

Espinoza

et al. 2016

Chemistry A European J

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Large aza-analogues of curved polycyclic aromatic hydrocarbons with a double-helicene structure present unique features for molecular photonics. We present the preparation and characterization of three such structures. The synthesis of these heterocyclic nanographenes involves only a few high-yield steps that use readily available starting materials. X-ray analysis revealed that each of these new dyes has three conformational isomers: one diastereoisomer in a meso form and two enantiomers in twisted forms [(P,P)] and [(M,M)]. The low energy barriers between the conformers, however, prevent their separation by using chiral HPLC, and the NMR spectra show only one set of signals for each of these curved compounds. Density functional theory (DFT) calculations quantify the small energy difference and the small energy barriers between the chiral and meso forms, which fully supports the experimental results. Their optical absorption lacks any sensitivity to the solvent environment, whereas their fluorescence features exhibit pronounced solvatochromism. This rarely observed solvatofluorochromism of centrosymmetric molecules without either electron-withdrawing groups or -donating substituents was probed by using time-resolved spectroscopy. These studies suggest that, similar to 9,9'-bianthryl, the nonpolar locally excited state shows negligible solvatochromism, whereas the charge-transfer state is sensitive to solvent polarity.

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Section: Resultsmentioning

confidence: 98%

Nonplanar Butterfly‐Shaped π‐Expanded Pyrrolopyrroles

Krzeszewski

Kodama

Espinoza

et al. 2016

Chemistry A European J

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“…The positions 1, 3, 6, and 8 ( Py N-C on Chart 1) are the most susceptible to electrophilic and radical substitutions. 72−74 Therefore, this study focuses on pyren-1-yl amides (Chart 1).…”

Section: Resultsmentioning

confidence: 99%

How Do Amides Affect the Electronic Properties of Pyrene?

et al. 2018

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The electronic properties of amide linkers, which are intricate components of biomolecules, offer a wealth of unexplored possibilities. Herein, we demonstrate how the different modes of attaching an amide to a pyrene chromophore affect the electrochemical and optical properties of the chromophore. Thus, although they cause minimal spectral shifts, amide substituents can improve either the electron-accepting or electron-donating capabilities of pyrene. Specifically, inversion of the amide orientation shifts the reduction potentials by 200 mV. These trends indicate that, although amides affect to a similar extent the energies of the ground and singlet excited states of pyrene, the effects on the doublet states of its radical ions are distinctly different. This behavior reflects the unusually strong orientation dependence of the resonance effects of amide substituents, which should extend to amide substituents on other types of chromophores in general. These results represent an example where the Hammett sigma constants fail to predict substituent effects on electrochemical properties. On the other hand, Swain–Lupton parameters are found to be in good agreement with the observed trends. Examination of the frontier orbitals of the pyrene derivatives and their components reveals the underlying reason for the observed amide effects on the electronic properties of this polycyclic aromatic hydrocarbon and points to key molecular-design strategies for electronic and energy-conversion systems.

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“…This phenomenon is different to cases involving organic sensitizers that have a high propensity for intersystem crossing (ISC), which either leads to the formation of triplet CT states, or does not allow CS if the triplet excitation energy is below the CT energy level . Such triplet CT manifolds have been known for quite some time, and they can affect the performance of organic devices …”

Section: Resultsmentioning

confidence: 96%

Is it common for charge recombination to be faster than charge separation?

Espinoza

Bao

Krzeszewski

et al. 2019

Int J of Chemical Kinetics

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Attaining long‐lived charge‐transfer (CT) states is of the utmost importance for energy science, photocatalysis, and materials engineering. When charge separation (CS) is slower than consequent charge recombination (CR), formation of a CT state is not apparent, yet the CT process provides parallel pathways for deactivation of electronically excited systems. The nuclear, or Franck‐Condon (FC), contributions to the CT kinetics, as implemented by various formalisms based on the Marcus transition‐state theory, provide an excellent platform for designing systems that produce long‐lived CT states. Such approaches, however, tend to underestimate the complexity of alternative parameters that govern CT kinetics. Here we show a comparative analysis of two systems that have quite similar FC CT characteristics but manifest distinctly different CT kinetics. A decrease in the donor‐acceptor electronic coupling during the charge‐separation step provides an alternative route for slowing down undesired charge recombination. These examples suggest that, while infrequently reported and discussed, cases where CR is faster than CS are not necessarily rare occurrences.

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Nitropyrene Photoprobes: Making Them, and What Are They Good for?

Cited by 23 publications

References 156 publications

Nonplanar Butterfly‐Shaped π‐Expanded Pyrrolopyrroles

Nonplanar Butterfly‐Shaped π‐Expanded Pyrrolopyrroles

How Do Amides Affect the Electronic Properties of Pyrene?

Is it common for charge recombination to be faster than charge separation?

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