Effects of conjugation length and resonance enhancement on two-photon absorption in phenylene–vinylene oligomers

Johnsen, Mette; Paterson, Martin J.; Arnbjerg, J.; Christiansen, Ove; Nielsen, Christian; Jørgensen, Mikkel; Ogilby, Peter R.

doi:10.1039/b715441k

Cited by 48 publications

(71 citation statements)

References 81 publications

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“…Similar to the effects of the conjugation length, 29,30 donor/acceptor substituents 20-22, 31, 32 and branching 26,33,34 on the optical properties of organic molecules, the type of ligands and ligand surface density can substantially affect the optical properties of small QDs.…”

Section: Nanoclustersmentioning

confidence: 96%

“…44 In contrast, optical spectra of the common conjugated organic molecules typically have only a few pronounced transitions. [29][30][31][32][33][34] This increase is attributed to the growth of the density of states further away from the band-gap, but not to an increase of the associated transition dipole moments themselves.…”

Section: Large-size Quantum Dotsmentioning

confidence: 99%

“…For example, variation of the conjugation length 29,30 allows for tuning transition energies and transition strength for both linear and nonlinear absorption.…”

mentioning

confidence: 99%

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Two-Photon Absorption in CdSe Colloidal Quantum Dots Compared to Organic Molecules

et al. 2014

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We discuss fundamental differences in electronic structure as reflected in one- and two-photon absorption spectra of semiconductor quantum dots and organic molecules by performing systematic experimental and theoretical studies of the size-dependent spectra of colloidal quantum dots. Quantum-chemical and effective-mass calculations are used to model the one- and two-photon absorption spectra and compare them with the experimental results. Currently, quantum-chemical calculations are limited to only small-sized quantum dots (nanoclusters) but allow one to study various environmental effects on the optical spectra such as solvation and various surface functionalizations. The effective-mass calculations, on the other hand, are applicable to the larger-sized quantum dots and can, in general, explain the observed trends but are insensitive to solvent and ligand effects. Careful comparison of the experimental and theoretical results allows for quantifying the range of applicability of theoretical methods used in this work. Our study shows that the small clusters can be in principle described in a manner similar to that used for organic molecules. In addition, there are several important factors (quality of passivation, nature of the ligands, and intraband/interband transitions) affecting optical properties of the nanoclusters. The larger-size quantum dots, on the other hand, behave similarly to bulk semiconductors, and can be well described in terms of the effective-mass models.

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Section: Nanoclustersmentioning

confidence: 96%

Section: Large-size Quantum Dotsmentioning

confidence: 99%

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Two-Photon Absorption in CdSe Colloidal Quantum Dots Compared to Organic Molecules

et al. 2014

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“…As a matter of fact, 2PA cross sections in semiconductor polymers are closely related to the effective numbers of π-electrons [18], the π-conjugation length [19], and the charge separation induced by introducing electron-donating and withdrawing groups [20]. These effects are associated with the transition dipole moment (μ) and dipole moment change (Δμ), which govern the 2PA cross section in organic materials [21].…”

Section: Introductionmentioning

confidence: 99%

Femtosecond Two-Photon Absorption Spectroscopy of Poly(fluorene) Derivatives Containing Benzoselenadiazole and Benzothiadiazole

et al. 2017

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We have investigated the molecular structure and two-photon absorption (2PA) properties relationship of two push–pull poly(fluorene) derivatives containing benzoselenadiazole and benzothiadiazole units. For that, we have used the femtosecond wavelength-tunable Z-scan technique with a low repetition rate (1 kHz) and an energy per pulse on the order of nJ. Our results show that both 2PA spectra present a strong 2PA (around 600 GM (1 GM = 1 × 10−50 cm4·s·photon−1)) band at around 720 nm (transition energy 3.45 eV) ascribed to the strongly 2PA-allowed 1Ag-like → mAg-like transition, characteristic of poly(fluorene) derivatives. Another 2PA band related to the intramolecular charge transfer was also observed at around 900 nm (transition energy 2.75 eV). In both 2PA bands, we found higher 2PA cross-section values for the poly(fluorene) containing benzothiadiazole unit. This outcome was explained through the higher charge redistribution at the excited state caused by the benzothiadiazole group as compared to the benzoselenadiazole and confirmed by means of solvatochromic Stokes shift measurements. To shed more light on these results, we employed the sum-over-states approach within the two-energy level model to estimate the maximum permanent dipole moment change related to the intramolecular charge transfer transition.

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“…These molecules are, however, comparatively small and not very interesting from a molecular design perspective in for example the design of molecules with large non-linear optical properties. Several reports have been made where changes of for example the TPA crosssection of a series of conjugated organic molecules have been rationalised quite successfully using calculations carried out with the response formulation and not considering solvent effects [32,33]. In particular, the solvent effect on the TPA cross-section of larger conjugated organic molecules has hardly been studied experimentally possibly due to the tedious experiments needed in order to obtain reliable results [34].…”

Section: Introductionmentioning

confidence: 98%

Optical properties of pyridine and methyl-pyridinium in water using DFT/MM

Nielsen¹,

Mikkelsen

2015

Molecular Physics

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Molecular properties such as excitation energies, polarisabilities and two-photon absorption cross-sections of pyridine and N-methyl-pyridinium embedded in a solvent of water are studied using density functional theory/molecular mechanics (DFT/MM) calculations. The purpose of this study is to study how well the differences between a cationic and a neutral specie can be predicted with water as the solvent. In order to answer this question, the DFT/MM method used is benchmarked in terms of convergence profiles, e.g. how many calculations are needed in order to obtain a statistically converged result. Quantification of for example how many water molecules needs to be included in the quantum mechanics system in the calculations before a converged molecular property is obtained which is also benchmarked. The latter will serve as valuable information in further calculations of larger organic molecules, where more experimental data are available. In this work, the calculated excitation energies are compared to experimentally determined ultraviolet/visible (UV/VIS) spectra of both pyridine and N-methyl-pyridinium and a reasonable agreement is found.

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Effects of conjugation length and resonance enhancement on two-photon absorption in phenylene–vinylene oligomers

Cited by 48 publications

References 81 publications

Two-Photon Absorption in CdSe Colloidal Quantum Dots Compared to Organic Molecules

Two-Photon Absorption in CdSe Colloidal Quantum Dots Compared to Organic Molecules

Femtosecond Two-Photon Absorption Spectroscopy of Poly(fluorene) Derivatives Containing Benzoselenadiazole and Benzothiadiazole

Optical properties of pyridine and methyl-pyridinium in water using DFT/MM

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