Study of hydrogen bonds and their influence on the optical and electrical properties of organic molecules in a solvent.

Author(s)

Nestor Cortez Saavedra Filho

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto de Física (IF/SBI)
• Defense date: 1999-10-05

Examining board members

Sylvio Roberto Accioly Canuto; Rogério Custódio; Luiz Carlos Gomide Freitas; Amando Siuiti Ito; Alfredo Mayall Simas

• Advisor: Sylvio Roberto Accioly Canuto

Abstract

The interest of this work is the study of hidrogen bonding and it influence on the electrical and optical properties of molecules in solvent media. Once that hydrogen bonding is a specific inte- raction between solute and solvent, continuum solvent models are not a appropiate choice to face this problem. Thus, we adopted a discrete solvent model that take into account each sol- vent molecule. We studied a class of organic molecules called azines that due the lone pair present in the ni- trogen atom, this molecules show hydrogen bonding with molecules of a protic solvent. A Monte Carlo simulation is performed in a number of polar and non-polar solvente molecules. Analisys of the solvent structure around each solute molecule is performed using the radial distribution function. Hydrogen bonding analysis between solute and solvent is also carried out. Supermolecular structures involving the solute and the nearest solvent molecules and, separa- tely, the hydrogen bonded molecules, are used as input to quantum mechanical semiempirical calculations of the first electronic absorption transition and the first hyperpolarisabilty. Only statistically non-correlated superstructures were used in the calculation. The results are analy- sed and compared to experimental and other theoretical results. The results show a remarkable contribution of the hydrogen bonding on the UVvisible spec- trum. As well as the solvatochromic shift, the change in the first hyperpolarizability is mainly due to the contribution of the nearest solvent molecule, which is involved on the hydrongen boding formation. (AU)