Katarzyna Piela

Helical superstructure and charged polarons contributions to optical nonlinearity of 2-methyl-4-nitroaniline crystals studied by resonance Raman, electron paramagnetic resonance, circular dichroism spectroscopies, and quantum chemical calculations.

The Raman excitation profiles of solid 2-methyl-4-nitroaniline (MNA) reveal several band enhancements by intermolecular and intramolecular charge transfer states. Calculated excited- and ground-state molecular geometries and excited state distortions qualitatively determined from Raman spectra indicate multiple vibrations leading to MNA dissociation. Also, overtones and combination tones can generate charged polarons, as detected by electron paramagnetic resonance after the exposure to 980 and 1550 nm laser diodes. The MNA space group Ia (C(s)(4)) is nonchiral; however, the electronic circular dichroism (CD) spectra of solution, KBr pellet, and single crystal were recorded. The crystal chirality is elucidated by room-temperature dynamic disorder, possible helical superstructure along the [102] polar axis, and charged polarons presence. The CD spectra ab initio calculations for MNA neutral and negatively charged monomers, dimers, and trimers, lying along the helix, confirmed the chirality. The role of these findings toward efficient optical nonlinearity and electric conductivity failure is discussed.

End-to-end self-assembly of gold nanorods in isopropanol solution: experimental and theoretical studies

We describe here a modification of properties of colloidal gold nanorods (NRs) resulting from the chemical treatment used to carry out their transfer into isopropanol (IPA) solution. The NRs acquire a tendency to attach one to another by their ends (end-to-end assembly). We focus on the investigation of the change in position and shape of the longitudinal surface plasmon (l-SPR) band after self-assembly. The experimental results are supported by a theoretical calculation, which rationalizes the dramatic change in optical properties when the NRs are positioned end-to-end at short distances. The detailed spectroscopic characterization performed at the consecutive stages of transfer of the NRs from water into IPA solution revealed the features of the interaction between the polymers used as ligands and their contribution to the final stage, when the NRs were dispersed in IPA solution. The efficient method of aligning the NRs detailed here may facilitate applications of the self-assembled NRs as building blocks for optical materials and biological sensing.Graphical Abstract

Optical nonlinearity and electric conductivity origin study on sucrose crystal by using IR, Raman, INS, NMR, and EPR spectroscopies.

The supposed importance of hydrogen bonds toward the origin of second harmonic generation (SHG) and electric conductivity in crystalline sucrose was investigated by IR (4000-10cm(-1)), INS (2000-10cm(-1), at 35K), polarized Raman (3600-50cm(-1)) spectra, and (1)H NMR second moment line records in the temperature range 450-80K. The temperature dependence of NIR (7000-5500cm(-1)) polarized spectra gave information about -CH2 motions complementary to NMR results concerning -CH2OH group rearrangements. The EPR spectra were applied to study the generation of radical ions by exposure to NIR radiation. Density functional theory quantum chemical calculations were performed to reproduce the vibrational spectra in order to complete as far as possible the assignments of bands observed by us and in the literature in sucrose crystals, and to throw more light on the possible reasons of sucrose electric conductivity and optical nonlinearity by the knowledge of theoretical values of dipole moments, polarizabilities, first order hyperpolarizabilities of sucrose molecule and clusters as well as ionization energy and electron affinity. The proton transfer in one specific hydrogen bond parallel to the helical axis b is proposed to be the most important in SHG and conductivity origin.