The exciton model in molecular spectroscopy

Kasha, Michael; Rawls, H. Ralph; El‐Bayoumi, M. Ashraf

doi:10.1351/pac196511030371

Cited by 3,987 publications

(3,774 citation statements)

References 1,044 publications

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“…This should in turn lead to a substantial distribution of excitonic interaction energies, hence to a broadening instead of a distinct splitting or shift of the absorption band. 55 Involvement of intermolecular aggregates can be safely ruled out as the absorption spectra were the same upon 5-fold dilution.…”

Section: Resultsmentioning

confidence: 99%

Excited-State Dynamics of Hybrid Multichromophoric Systems: Toward an Excitation Wavelength Control of the Charge Separation Pathways

et al. 2009

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The photophysical properties of two hybrid multichromophoric systems consisting of an oligophenylethynyl (OPE) scaffold decorated by 10 red or blue naphthalene diimides (NDIs) have been investigated using femtosecond spectroscopy. Ultrafast charge separation was observed with both red and blue systems. However, the nature of the charge-separated state and its lifetime were found to differ substantially. For the red system, electron transfer occurs from the OPE scaffold to an NDI unit, independently of whether the OPE or an NDI is initially excited. However, charge separation upon OPE excitation is about 10 times faster, and takes place with a 100 fs time constant. The average lifetime of the ensuing charge-separated state amounts to about 650 ps. Charge separation in the blue system depends on which of the OPE scaffold or an NDI is excited. In the first case, an electron is transferred from the OPE to an NDI and the hole subsequently shifts to another NDI unit, whereas in the second case symmetry-breaking charge separation between two NDI units occurs. Although the charges are located on two NDIs in both cases, different recombination dynamics are observed. This is explained by the location of the ionic NDI moieties that depends on the charge separation pathway, hence on the excitation wavelength. The very different dynamics observed with red and blue systems can be accounted for by the oxidation potentials of the respective NDIs that are higher and lower than that of the OPE scaffold. Because of this, the relative energies of the two charge-separated states (hole on the OPE or an NDI) are inverted.

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Section: Resultsmentioning

confidence: 99%

Excited-State Dynamics of Hybrid Multichromophoric Systems: Toward an Excitation Wavelength Control of the Charge Separation Pathways

et al. 2009

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“…This reduced representation of the protein vibrations, the amide I subspace, is spanned by the local amide I vibrations of each peptide unit. 11 The Hamiltonian for a system of amide I oscillators can be described using the exciton model, [41][42][43][44][45] which is analogous to the "floating oscillator model" utilized to describe the amide I band of proteins by Torii and Tasumi. 11,44,46 The diagonal elements of the Hamiltonian matrix are the intrinsic frequencies of the uncoupled, local amide I vibrations.…”

Section: Amide I Band Calculationmentioning

confidence: 99%

Optimization of Model Parameters for Describing the Amide I Spectrum of a Large Set of Proteins

2012

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A new simulation protocol for the prediction of the infrared absorption of the amide I vibration of proteins was developed. The method incorporates known effects on the intrinsic frequencies (backbone conformation, inter-peptide and peptide-solvent hydrogen bonding) and couplings (nearest neighbor coupling, transition dipole coupling) of amide I oscillators in a parametrized manner. Model parameters for the simulation of amide I spectra were determined through fitting and optimization of simulated spectra to experimentally measured infrared spectra of 44 proteins that represent maximum structural variation in terms of different folds and secondary structure contents. Prediction of protein spectra using the optimized parameters resulted in good agreement with experimental spectra and in a considerable improvement compared to a description involving only transition dipole coupling.

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“…Derivatives with long alkyl side chains attached to the nonpe-A C H T U N G T R E N N U N G ripheral sites (1,4,8,11,15,18,22,25) also form columnar liquid crystals (Pc series 3). [14,15] However, nonperipheral substitution with alkoxy side chains (Pc series 4) [16] does not result in mesogenic phthalocyanines and aggregation of the aromatic cores is suppressed in the solid state.…”

Section: Introductionmentioning

confidence: 99%

“…In contrast, self-assembly into columnar aggregates broadens and blueshifts the Q-band as a result of exciton interactions. [18,19] Therefore, in order to obtain solid phthalocyanines that demonstrate similar light absorption characteristics to those of their dilute solutions, it was an attractive objective to place alkyl side chains on the macrocycle in such a way as to strongly disfavour aggregation but without perturbing the basic phthalocyanine chromophore. [20,21] The chosen strategy was to attach the alkyl chains to five-membered rings fused to the peripheral sites of the phthalocyanine so that the chains would project out of the molecular plane of the macrocycle and enforce separation through mutual steric interference.…”

Section: Introductionmentioning

confidence: 99%

The Self‐Ordering Properties of Novel Phthalocyanines with Out‐of‐Plane Alkyl Substituents

McKeown

Helliwell

Hassan

et al. 2006

Chemistry A European J

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Two novel homologous series of phthalocyanines were prepared from 2,2‐dialkylindane and 2,2‐dialkyl‐1,3‐benzodioxole precursors. It was anticipated that attaching alkyl chains to five‐membered rings, fused to the peripheral sites of the phthalocyanine ring, would result in the adoption of an out‐of‐plane configuration and thereby discourage cofacial aggregation, to provide an analogy with picket‐fence porphyrins. This strategy proved partially successful. Some members of the series of phthalocyanines derived from 2,2‐dialkyl‐1,3‐benzodioxoles, in which the alkyl chains are linked to the phthalocyanine via a cyclic ketal, form spin‐coated thin films in which the phthalocyanine cores are perfectly isolated. This behaviour is associated with the formation of a disordered crystal that appears as a mesophase in the thermal profile of these materials. However, the phthalocyanines derived from 2,2‐dialkylindanes display a columnar mesophase over a wide temperature range, with some liquid crystalline derivatives at ambient temperature. A single‐crystal X‐ray diffraction structure of the octahexyl derivative of this series shows how the columnar assembly accommodates the out‐of‐plane alkyl chains by tilting the macrocyclic plane of the phthalocyanine components with respect to the axis of the column. This study helps to emphasise the importance of both the steric and electronic effects of substituents on the packing behaviour of phthalocyanines in the condensed phase, and especially the role of electron‐donating oxygen atoms directly attached to the ring.

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The exciton model in molecular spectroscopy

Cited by 3,987 publications

References 1,044 publications

Excited-State Dynamics of Hybrid Multichromophoric Systems: Toward an Excitation Wavelength Control of the Charge Separation Pathways

Excited-State Dynamics of Hybrid Multichromophoric Systems: Toward an Excitation Wavelength Control of the Charge Separation Pathways

Optimization of Model Parameters for Describing the Amide I Spectrum of a Large Set of Proteins

The Self‐Ordering Properties of Novel Phthalocyanines with Out‐of‐Plane Alkyl Substituents

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