High-resolution electronic spectra of tetrahelicene and hexahelicene in low-temperature polycrystalline matrices

Palewska, Krystyna; Ruziewicz, Z.; Chojnacki, Henryk; Meister, Erich C.

doi:10.1016/0301-0104(92)80159-s

Cited by 5 publications

(5 citation statements)

References 20 publications

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“…The onsets of the absorption spectra correspond to the (electronic) adiabatic transition energies that are impacted in addition by the difference in zero-point energies, solvent polarization, and stabilization due to coupling to intramolecular low-frequency vibrations. When taking into account the anticipated solvent shifts (the measured solvent-dependent onset of absorption and fluorescence in H5 is scattered within 0.1 eV) 9,11,25,47,48 and the zero-point differences of 82-92 meV (from summation over all normal modes in S 1 and S 0 ), we found that the calculated adiabatic TD-DFT transition energies (for a complete set of values, see the table in the Supporting Information) tend to overestimate the observed absorption onsets (Table 1) by less than 0.2 eV.…”

Section: Methodsmentioning

confidence: 99%

“…Processes associated with spin−orbit coupling in aromatic compounds of aza-helicene type are expected to be influenced by two major contributions. On one hand, departure from coplanarity is considered to be responsible for the enhancement of ISC observed in [ n ]helicenes from n = 3 to n = 7 rings, whose luminescence properties, including phosphorescence, have been comprehensively studied; − the ISC rates observed in oligo(phenylene ethynylene)s and oligothiophenes were also shown to originate from nonplanarity of the molecules . According to Sapir and Vander Donckt, the intersystem crossing rates for H5 are intrinsically larger than those for planar phenanthrene.…”

Section: Introductionmentioning

confidence: 99%

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Intersystem Crossing Processes in Nonplanar Aromatic Heterocyclic Molecules

et al. 2007

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A comprehensive study of the photophysical properties of a series of monoaza[5]helicenes is presented on the basis of joint optical spectroscopy and quantum chemistry investigations. The molecules have been characterized by absorption and CW/time-resolved luminescence measurements. All quantities related to spin-orbit-coupling processes, such as intersystem crossing rates and radiative phosphorescence lifetimes, were found to depend strongly on the nitrogen position within the carbon backbone. Density functional theory and semiempirical quantum-chemical methods were used to evaluate the molecular geometries, the characteristics of the excited singlet and triplet states, and the spin-orbit coupling matrix elements. We demonstrate that the magnitude of spin-orbit coupling is directly correlated with the degree of deviation from planarity. The trends from the calculated photophysical quantities, namely, radiative fluorescence and phosphorescence decay rates and intersystem crossing rates, of the mono-aza-helicenes are fully consistent with experiment.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Intersystem Crossing Processes in Nonplanar Aromatic Heterocyclic Molecules

et al. 2007

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“…The emission properties have been discussed in the literature for [n]helicenes with n ) 4-7 rings 1,[6][7][8][9][10][11][12] and bisubstituted [5]helicenes 13 with a focus on intersystem crossing. The recently synthesized mono-aza- [5]helicene molecules 14 (see Figure 1) show a more efficient intersystem crossing than in the unsubstituted [5]helicene (H5); 15 in these molecules, a nitrogen atom has been introduced into the [5]helicene carbon backbone at positions 1-7, as illustrated in Figure 1, to form the monoaza-derivatives 1-aza-H5 -7-aza-H5.…”

Section: Introductionmentioning

confidence: 99%

Excited-State Properties and Emission Spectra of Nonplanar Heterocyclic Helicenes

et al. 2006

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We discuss the electron-vibration coupling in mono-aza-[5]helicenes on the basis of a Franck-Condon analysis and density functional theory (DFT) calculations of the fluorescence and phosphorescence spectra measured in ethanol. The geometries of the initial states were obtained from time-dependent DFT (S(1)) and unrestricted DFT (T(1)) excited-state optimizations. In general, the position of the nitrogen atom has only a minor impact on the vibronic fine-structure in both absorption and emission. The shapes of the emission spectra from the lowest singlet and triplet states are found to be determined by contributions from multiple normal modes. The results of the calculations demonstrate how the interplay among these normal modes results in qualitatively and quantitatively different spectra for fluorescence and phosphorescence.

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“…Palewska et al have obtained the high resolution fluorescence and phosphorescence spectra of tetrahelicene and hexahelicene in nheptane matrix at room temperature. 19 They find the singlet-singlet transition to be at 3.1 eV whereas the singlet-triplet transition to be at 2.5 eV. The electronic absorption spectrum of chrysene molecule in boric acid glass matrix is reported by Hussain.…”

Section: Introductionmentioning

confidence: 88%

“…These astronomical bands can be explained with electronic absorptions and/or dynamical methods such as electronic relaxation and intramolecular vibrational relaxation. Palewska et al obtained high-resolution fluorescence and phosphorescence spectra of tetrahelicene and hexahelicene in n -heptane matrix at room temperature . They found the singlet–singlet transition to be at 3.1 eV, and the singlet–triplet transition at 2.5 eV.…”

Section: Introductionmentioning

confidence: 99%

Correlated Electronic States of a Few Polycyclic Aromatic Hydrocarbons: A Computational Study

2019

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In recent years Polycyclic Aromatic Hydrocarbons (PAHs) have been studied for their electronic properties as they are viewed as nanodots of graphene. They have also been of interest as functional molecules for applications such as light emitting diodes and solar cells.Since last few years varying structural and chemical properties corresponding to the size and geometry of these molecules have been studied both theoretically and experimentally.In this paper, we carry out a systematic study of the electronic states of several PAHs using the Pariser-Parr-Pople model which incorporates long-range electron correlations. In all the molecules studied by us, we find that the 2A state is below the 1B state and hence none of them will be fluorescent in the gaseous phase. The singlet-triplet gap is more than one-half of the singlet-singlet gap in all cases and hence none of these PAHs can be candidates for improved solar cell efficiencies in a singlet fission. We discuss in detail the properties of the electronic states which include bond orders and spin densities (in triplets) of these systems.

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High-resolution electronic spectra of tetrahelicene and hexahelicene in low-temperature polycrystalline matrices

Cited by 5 publications

References 20 publications

Intersystem Crossing Processes in Nonplanar Aromatic Heterocyclic Molecules

Intersystem Crossing Processes in Nonplanar Aromatic Heterocyclic Molecules

Excited-State Properties and Emission Spectra of Nonplanar Heterocyclic Helicenes

Correlated Electronic States of a Few Polycyclic Aromatic Hydrocarbons: A Computational Study

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