Oxazole Dyes With Potential For Photoluminescence Bioprobes: A Two-Photon Absorption Study

In this work, six π-conjugated oxazole compounds dissolved in dichloromethane were characterized with linear and nonlinear optical measurements. Z-scan with femtosecond laser pulses was employed to determine the two-photon absorption (TPA) spectra. Other photophysical parameters, such as absorbance, solvatochromism, lifetime fluorescence, and fluorescence anisotropy, were evaluated with linear optical techniques. The experimental TPA cross section spectra were adjusted by the sum-over-states (SOS) model, by which important parameters such as transition dipole moments and broadening parameters were determined. To better understand the TPA spectra of the oxazole compounds, quantum-chemical calculations using the response function formalism and the density functional theory level of theory were performed. Using the results provided by the quantum-chemical calculations and the broadening parameters estimated through the application of the SOS model, the TPA spectra were simulated by the superposition (summation) of individual homogeneous Lorentzian absorption profiles

Investigation of the Second Harmonic Generation at the Water–Vacuum Interface by Using Multi‐Scale Modeling Methods

Abstract The Sequential Quantum Mechanics/Molecular Mechanics scheme has been enacted to perform a systematic investigation of the polarizability (α) and first hyperpolarizability (β) responses at the water–vacuum interface. After performing classical molecular dynamics simulations to provide snapshots of the structures, quantum chemistry calculations of the linear and nonlinear optical responses have been performed for clusters of five water molecules at the time‐dependent DFT level in combination with different embedding schemes, ranging from point charges to polarizable point charges, with and without local field effects. When going from the bulk to the interface, the main observations of these calculations encompass i) a modest increase of the average polarizability but an increase by about a factor of two of its anisotropy, ii) an increase by about 20 % of the βHRS response, accompanied by a small increase of its depolarization ratio, and iii) a net increase of the component of the β tensor normal to the interface (βzzz) as well as of β//. Globally, the interfacial effects on β are localized at the first molecular layer while they are observed up to the fourth molecular layer on α

Investigation of the Second Harmonic Generation at the Water–Vacuum Interface by Using Multi‐Scale Modeling Methods

Abstract Invited for this month′s cover picture are Dr. Tárcius N. Ramos and Prof. Benoît Champagne at the University of Namur (Belgium). The cover picture shows the interfacial selectivity of second harmonic generation at the water‐vacuum interface, which is targeted in this work. In more details, the molecular first hyperpolarizability responses have been calculated by combining classical molecular dynamics and quantum chemistry simulations, and our model was able to distinguish between the bulk and the interfacial contributions. Read the full text of their Research Article at 10.1002/open.202200045