| 1. |
- Zalesny, Robert, et al.
(författare)
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Resonant and Nonresonant Hyperpolarizabilities of Spatially Confined Molecules : A Case Study of Cyanoacetylene
- 2013
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Ingår i: Journal of Chemical Theory and Computation. - : American Chemical Society (ACS). - 1549-9618 .- 1549-9626. ; 9:8, s. 3463-3472
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Tidskriftsartikel (refereegranskat)abstract
- In this theoretical study we report on resonant and nonresonant electric-dipole (hyper)polarizabilities of cyanoacetylene molecule confined by repulsive potentials of cylindrical symmetry mimicking a topology of nanotubelike carbon cages. The set of investigated electronic properties encompasses dipole moment, polarizability, first and second hyperpolarizability as well as the two-photon transition matrix elements. The effect of external potential on vibrational contributions to electric-dipole properties is also included in our treatment. The computations are performed at several levels of theoretical approximation including state-of-the-art coupled-cluster (CCSD(T)) and multireference configuration interaction methods (MRCISD(Q)). The results of calculations presented herein indicate that the decrease in dipole moment observed experimentally for the HCCCN molecule solvated in helium nanodroplets may be partially attributed to the confinement effects. The external confining potential causes a substantial drop of the isotropic average electronic polarizability and second hyperpolarizability. In contrast, the vector component of the electronic first hyperpolarizability substantially increases. Nuclear relaxation contributions to all studied electric-dipole properties are found to diminish upon confinement. Our calculations also indicate that the most intense (1)Sigma(+) <- (X) over tilde one-photon transition is slightly blue-shifted whereas the corresponding oscillator strength is virtually unaffected upon confinement. Interestingly, the absolute magnitude of the diagonal component of the second-order transition moment for the bright state (S-zz(0 -> 1)Sigma(+)) increases with the strength of external potential. The effect of structural relaxation on the electric-dipole properties, arising from the presence of the external potential, is also investigated in the present work.
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| 2. |
- Ahmadzadeh, Karan, et al.
(författare)
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Toward Accurate Two-Photon Absorption Spectrum Simulations: Exploring the Landscape beyond the Generalized Gradient Approximation
- 2024
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Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 15:4, s. 969-974
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Tidskriftsartikel (refereegranskat)abstract
- In this Letter, we present a pioneering analysis of the density functional approximations (DFAs) beyond the generalized gradient approximation (GGA) for predicting two-photon absorption (2PA) strengths of a set of push-pull π-conjugated molecules. In more detail, we have employed a variety of meta-generalized gradient approximation (meta-GGA) functionals, including SCAN, MN15, and M06-2X, to assess their accuracy in describing the 2PA properties of a chosen set of 48 organic molecules. Analytic quadratic response theory is employed for these functionals, and their performance is compared against the previously studied DFAs and reference data obtained at the coupled-cluster CC2 level combined with the resolution-of-identity approximation (RI-CC2). A detailed analysis of the meta-GGA functional performance is provided, demonstrating that they improve upon their predecessors in capturing the key electronic features of the π-conjugated two-photon absorbers. In particular, the Minnesota functional MN15 shows very promising results as it delivers pleasingly accurate chemical rankings for two-photon transition strengths and excited-state dipole moments.
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| 3. |
- Arul Murugan, N., et al.
(författare)
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Unusual binding-site-specific photophysical properties of a benzothiazole-based optical probe in amyloid beta fibrils
- 2018
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : The Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 20:31, s. 20334-20339
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Tidskriftsartikel (refereegranskat)abstract
- Optical imaging of amyloid fibrils serves as a cost-effective route for the diagnosis of Alzheimer-like conformational diseases. However{,} the challenge here is to optimize the binding affinity and photophysical properties of the optical imaging agents in a way specific to certain types of amyloids. In a few occasions it is shown that novel optical imaging agents can be designed to bind to a particular type of amyloid fibril with larger binding affinity and specificity. There is also a recent report on photoluminescent polythiophenes which display photophysical properties that can be used to distinguish the variants or subtypes of amyloids (J. Rasmussen et al.{,} Proc. Natl. Acad. Sci. U. S. A.{,} 2017{,} 114(49){,} 13018–13023). Based on a multiscale modeling approach{,} here{,} we report on the complementary aspect that the photophysical properties of a benzothiazole based optical probe (referred to as BTA-3) can be specific to the binding sites in the same amyloid fibrils and we attribute this to its varying electronic structure in different sites. As reported experimentally from competitive binding assay studies for many amyloid staining molecules and tracers{,} we also show multiple binding sites in amyloid fibrils for this probe. In particular{,} BTA-3 displayed a red-shift in its low-frequency absorption band only in site-4{,} a surface site of amyloid fibrils when compared to the spectra in water solvent. In the remaining sites{,} it exhibited a less significant blue shift for the same absorption band.
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| 4. |
- Bednarska, Joanna, et al.
(författare)
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Elucidating the Mechanism of Zn2+ Sensing by a Bipyridine Probe Based on Two-Photon Absorption
- 2016
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 120:34, s. 9067-9075
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we examine, by means of computational methods, the mechanism of Zn2+ sensing by a bipyridine-centered, D-pi-A-pi-D-type-ratiometric molecular probe. According to recently published experimental data [Divya, K. P.; Sreejith, S.; Ashokkumar, P.; Yuzhan, K.; Peng, Q; Maji, S. K.; Tong, Y.; Yu, H.; Zhao, Y.; Ramamurthy, P.; Ajayaghosh, A. A ratiometric fluorescent molecular -probe with enhanced two-photon response upon Zn2+ binding for in vitro and in vivo: bioimaging.= Chem. Sci. 2014, S, 3469-3474], after coordination to zinc ions the -probe exhibits a large enhancement of the two -photon absorption cross section. The goal of our investigation was to elucidate the mechanism behind this phenomenon. For this purpose, linear and nonlinear optical properties of -the unbound (cation-free) and bound probe were calculated, including the influence of solute Solvent interactions, implicitly using a polarizable continuum model and exp-licitely employing the QM/MM approach. Because the results of the calculations indicate that many conformers of the probe are energetically accessible at room temperature in solution and hence contribute to the Signal, structurepteperty relationships were also taken into account. Results of our simulations-demonstrate that the one-photon absorption bands for both the unbound -and bound forms correspond to the bright pi -> pi* transition to the first excited state; which, on the other hand,. exhibits negligible two-photon activity. On the basis of the results of the quadratic respOnse calculations, we put forward-notion that it is the second excited state that gives the strong signal in the experimental nonlinear spectrum. To explain the differenCes in the two-photon absorption activity for the two lowest-lying excited states and nonlinear response enhancement upon binding, we employed the generalized few -state model including the ground, first, and- second excited states. The analysis of the optical channel suggests that the large two-photon response is due to the coordination -induced increase of the, transition- moment from the first to the second excited state.
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| 5. |
- Bednarska, Joanna, et al.
(författare)
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Nonempirical Simulations of Inhomogeneous Broadening of Electronic Transitions in Solution : Predicting Band Shapes in One- and Two-Photon Absorption Spectra of Chalcones
- 2017
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Ingår i: Molecules. - : MDPI AG. - 1431-5157 .- 1420-3049. ; 22:10
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Tidskriftsartikel (refereegranskat)abstract
- We have examined several approaches relying on the Polarizable Embedding (PE) scheme to predict optical band shapes for two chalcone molecules in methanol solution. The PE-TDDFT and PERI-CC2 methods were combined with molecular dynamics simulations, where the solute geometry was kept either as rigid, flexible or partly-flexible (restrained) body. The first approach, termed RBMD-PE-TDDFT, was employed to estimate the inhomogeneous broadening for subsequent convolution with the vibrationally-resolved spectra of the molecule in solution determined quantum-mechanically (QM). As demonstrated, the RBMD-PE-TDDFT/QM-PCM approach delivers accurate band widths, also reproducing their correct asymmetric shapes. Further refinement can be obtained by the estimation of the inhomogeneous broadening using the RBMD-PERI-CC2 method. On the other hand, the remaining two approaches (FBMD-PE-TDDFT and ResBMD-PE-TDDFT), which lack quantum-mechanical treatment of molecular vibrations, lead to underestimated band widths. In this study, we also proposed a simple strategy regarding the rapid selection of the exchange-correlation functional for the simulations of vibrationally-resolved one-and two-photon absorption spectra based on two easy-to-compute metrics.
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| 6. |
- Bednarska, Joanna, et al.
(författare)
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Two-photon absorption of BF2-carrying compounds : insights from theory and experiment
- 2017
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 19:8, s. 5705-5708
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Tidskriftsartikel (refereegranskat)abstract
- This communication presents a structure-property study of a few novel pyridine-based difluoroborate compounds with a N-BF2-O core, which exhibit outstanding fluorescence properties. To exploit their potential for two-photon bioimaging, relationships between the two-photon action cross section and systematic structural modifications have been investigated and unravelled.
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| 7. |
- Knysh, Iryna, et al.
(författare)
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Less is more: on the effect of benzannulation on the solid-state emission of difluoroborates
- 2021
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Ingår i: Journal of Materials Chemistry C. - : ROYAL SOC CHEMISTRY. - 2050-7526 .- 2050-7534. ; 9:44, s. 15820-15830
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the emission properties of four organic dyes containing a strong electron-donating N(CH3)(2) group and an NBF2O-bearing heterocyclic moiety acting as the electron-accepting group. The four studied compounds differ in the number and positions of the fused benzo rings included in the heterocyclic moiety. They exhibit strong emission in solution, with fluorescence quantum yields (phi(f)) systematically exceeding 0.8 at least in one of the solvents used, regardless of the benzannulation architecture. The strong dipolar character, achieved by substitution with the N(CH3)(2) group and benzannulation, enhances the photoinduced charge transfer and appears to be an effective strategy to tune the photophysical properties of these dyes in solution. Indeed, red-shifted absorption spectra are obtained without deteriorating the emission properties. However, the present joint theory-experiment study clearly demonstrates that such a molecular design is not effective for solid-state applications, as only one derivative still exhibits significant emission in the crystalline form, namely the most compact one. We show that the combination of benzannulation in the presence of the strong amino donor leads to substantial changes in crystal packing and that a different network of intermolecular interactions can be found in the crystal. More specifically, going from the parent compound to its benzannulated derivatives induces a stronger pi MIDLINE HORIZONTAL ELLIPSIS pi stacking combined with multiple CHMIDLINE HORIZONTAL ELLIPSIS pi interactions involving the fused benzo rings and the hydrogen atoms of the dimethylamino group, which impedes efficient emission of the crystals.
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| 8. |
- List, Nanna Holmgaard, et al.
(författare)
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Relation between Nonlinear Optical Properties of Push-Pull Molecules and Metric of Charge Transfer Excitations
- 2015
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Ingår i: Journal of Chemical Theory and Computation. - : American Chemical Society (ACS). - 1549-9618 .- 1549-9626. ; 11:9, s. 4182-4188
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Tidskriftsartikel (refereegranskat)abstract
- We establish the relationships between the metric of charge transfer excitation (Delta r) for the bright pi pi* state and the two-photon absorption probability as well as the first hyperpolarizability for two families of push pull pi-conjugated systems. As previously demonstrated by Guido et al. (J. Chem. Theory Comput. 2013, 9, 3118-3126), Delta r is a measure for the average hole electron distance upon excitation and can be used to discriminate between short- and long-range electronic excitations. We indicate two new benefits from using this metric for the analyses of nonlinear optical properties of push pull systems. First, the two-photon absorption probability and the first hyperpolarizability are found to be interrelated through Delta r; if, beta similar to (Delta r)(k), then roughly, delta(TPA) similar to (Delta r)(k+1). Second, a simple power relation between Delta r and the molecular hyperpolarizabilities of push pull systems offers the possibility of estimating properties for longer molecular chains without performing calculations of high-order response functions explicitly. We further demonstrate how to link the hyperpolarizabilities with the chain length of the push-pull pi-conjugated systems through the metric of charge transfer.
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| 9. |
- Matczyszyn, Katarzyna, et al.
(författare)
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One- and Two-Photon Absorption of a Spiropyran-Merocyanine System : Experimental and Theoretical Studies
- 2015
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 119:4, s. 1515-1522
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Tidskriftsartikel (refereegranskat)abstract
- We report on the nonlinear optical properties measurements and quantum-chemical calculations of a well-known photochromic system consisting of spiropyran and the merocyanine photoproduct. The study of nonlinear absorption and refraction properties of the molecules dissolved in chloroform were performed with the Z-scan technique, using femtosecond pulses in a wide range of wavelengths. Maxima in the two-photon absorption spectrum at 700 and 1050 nm were found for the merocyanine form, and the corresponding two-photon absorption cross section is 80 GM and 20 GM, respectively. The latter feature does not vanish completely in the nonlinear spectrum of the spiropyran form, possibly because of the existence of some photoconversion caused by the laser beam during the measurements. A nonlinear absorption peak at 900 nm is found in the spiropyran form with an effective cross section of about 20 GM; it is likely due to three-photon absorption or to absorption by some intermediate species. The experimental data are supported by calculations performed with the use of a hybrid quantum mechanics-molecular mechanics approach.
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| 10. |
- Murugan, Natarajan Arul, et al.
(författare)
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Chelation-Induced Quenching of Two-Photon Absorption of Azacrown Ether Substituted Distyryl Benzene for Metal Ion Sensing
- 2014
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Ingår i: Journal of Chemical Theory and Computation. - : American Chemical Society (ACS). - 1549-9618 .- 1549-9626. ; 10:2, s. 778-788
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Tidskriftsartikel (refereegranskat)abstract
- Imaging of metal ion concentration, distribution, and dynamics can pave the way to diagnose a number of diseases and to identify the normal functioning of the human body. Recently, two-photon microscopy-based imaging of metal ions has become popular due to several favorable factors as compared to fluorescence-based imaging. However, much has to be investigated in order to design probes with large two-photon absorption cross sections and yet with selective binding affinity toward metal ions. In particular, it is crucial to recognize the mechanisms of metal ion-induced changes of the two-photon absorption intensity. The present paper contributes to this effort and reports on the results of extensive studies carried out to define a reliable computational protocol that can account for sampling, solvent, and finite temperature,effects for one- and two-photon properties of metal probes, using azacrown ether substituted distyrylbenzene embedded in solvents as a testbed. We employ a selection of theoretical approaches to model the structure of the probe alone and in the presence of Mg2+ ion in acetonitrile solvent, including static quantum-chemical calculations, rigid- and flexible-body molecular dynamics, and hybrid QM/MM molecular dynamics. For a set of solute-solvent configurations, the one- and the two-photon properties are computed using the recently developed polarizable embedding response approach. It is found that the hybrid QM/MM molecular dynamics based approach is the most successful one among other employed computational strategies, viz, reproduction of the metal ion-induced blue shift in the absorption wavelength and decrease in the two-photon absorption cross section, which actually is in excellent agreement with experimental data. The mechanism for such metal ion-induced changes in the optical properties is put forward using a few-state model. Possible design principles to tune the two-photon absorption properties of probes are also discussed.
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