Theoretical study on the relationship between the position of the substituent and the ESIPT fluorescence characteristic of HPIP

The influences of the substituent base position on the excited state intramolecular proton transfer fluorescence properties were explored in 2-(2'-hydroxyphenyl)imidazo[1,2-a]-pyridine(HPIP)and HPIP's derivatives(5'Br-HPIP and 6'BrHPIP).And the density functional theory(DFT)and time-dependent DFT(TD-DFT)methods were used to calculate the molecule structures.The calculated results showed that the influence of 5'Br-HPIP on the fluorescence intensity is stronger than that of 6'Br-HPIP.The fluorescence emission peak of 5'Br-HPIP occurred a blue shift compared with HPIP,and 6'BrHPIP exhibited an opposite red shift.The change of the fluorescence emission peak was attributed to the decrease of the energy gap from 6'Br-HPIP to 5'Br-HPIP.Our work on the substituent position influence could be helpful to design and develop new materials.     

Femtosecond laser-induced Cu plasma spectra at different laser polarizations and sample temperatures

Laser-induced breakdown spectroscopy (LIBS) is a good technique for detecting and analyzing material elements due to the plasma emission produced by the high-power laser pulse. Currently, a significant topic of LIBS research is improving the emission intensity of LIBS. This study investigated the effect of laser-polarization on femtosecond laser-ablated Cu plasma spectra at different sample temperatures. The measured lines under circularly polarized lasers were higher than those under linearly and elliptically polarized lasers. The enhancement effect was evident at higher Cu temperatures when comparing the plasma spectra that have circular and linear polarizations for different target temperatures. To understand the influence of laser-polarization and sample temperature on signal intensity, we calculated the plasma temperature (PT) and electron density (ED) . The change in PT and ED was consistent with the change in the atomic lines as the laser polarization was being adjusted. When raising the Cu temperature, the PT increased while the ED decreased. Raising the Cu temperature whilst adjusting the laser-polarization is effective for improving the signal of femtosecond LIBS compared to raising the initial sample temperature alone or only changing the laser polarization.