Supramolecular Approach to Tuning the Photophysical Properties of Quadrupolar Squaraines

In the present study, the influence of the hydrogen bonding for the one- and two-photon absorption of the prototypical squaraine dye is investigated with quantum chemistry tools. The central squaraine unit is bound by strong hydrogen bonds with 4-substituted N,N′-diphenylurea and, alternatively, N,N′-diphenylthiourea molecules, which affects to a high extend the properties of the squaraine electron accepting moiety, thus shifting its maximum absorption wavelength and enhancing the TPA cross section. The replacement of oxygen by sulfur atoms in the squaraine central ring, known to affect its photophysical behavior, is considered here as the way of modifying the strength and nature of the intermolecular contacts. Additionally, the influence of the oxygen-by-sulfur replacement is also considered in the N,N′-diphenylurea moiety, as the factor affecting the acidity of the N–H protons. The introduction of the sequence of the substituents of varying electron-donating or electron-withdrawing characters in the position 4 of N,N′-diphenyl(thio)urea subsystems allows to finely tune the hydrogen bonding with the central squaraine unit by further modification of the N–H bond characteristics. All of these structural modifications lead to the controlled adjustment of the electron density distribution, and thus, the properties affected such as transition moments and absorption intensity. Ab initio calculations provide strong support for this way of tailoring of one- or two-photon absorption due to the obtained strong hypsochromic shift of the maximum one-photon absorption wavelength observed particularly for thiosquaraine complexes and an increase in the TPA wavelength together with the increase in the TPA cross section. Moreover, the source of the strong modification of the thiosquaraine OPA in contrast to the pristine oxosquaraine upon N,N′-diphenyl(thio)urea substitution is determined. Furthermore, for the first time, the linear dependence of the non-additivity in the interaction energy on the Hammett substituent constant is reported. The stronger the electron-donating character of the substituent, the larger the three-body non-additive components and the larger their percentage to the total interaction energy.

High Hydrogen Ion Concentration Causes a Blue Shift in Gold Nanoparticles

In this research, our team used a rare electrochemical method to obtain gold nanoparticles (GNPs). The growth solution has been added with nitric acid in order to observe the effect of GNPs. The solution also included cetyltrimethylammonium bromide (CTAB) and acetone. All reactions involved the oxidation of acetone and chain polymerization. Therefore, the GNPs changed to a su pramolecular structure. In addition, our team measured absorption wavelength via ultraviolet/ visible spectrophotometer and found an obviously blue shift. This short absorption wavelength is obviously different from other GNPs.

Inscribing diffraction grating inside silicon substrate using a subnanosecond laser in one photon absorption wavelength

Using focused subnanosecond laser pulses at $$1.064\,\upmu \hbox {m}$$ 1.064 μ m wavelength, modification of silicon into opaque state was induced. While silicon exhibits one-photon absorption at this wavelength, the modification was induced inside $$300\,\upmu \hbox {m}$$ 300 μ m -thick silicon substrate without damaging top or bottom surfaces. The depth range of the focus position was investigated where inside of the substrate can be modified without damaging the surfaces. Using this technique, diffraction gratings were inscribed inside silicon substrate. Diffraction from the gratings were observed, and the diffraction angle well agreed with the theoretical value. These results demonstrate that this technique could be used for fabricating infrared optical elements in silicon.