Modeling electrostatic interactions in complex systems

Abstract

The study of novel molecular materials provides great opportunities to solve a large amounts of needs. A careful arrangement of molecules at the nanoscale can lead to the formation of systems with unique optical, electrical and magnetic properties. Purpose of this thesis is the study and integration of novel methodologies to get a deep understanding of intermolecular electrostatic interactions in complex nanosized systems. In Chapter 1 we investigate resonant energy transfer for a pair of dyes linked to a calixarene scaffold. We make extensive use of MD simulations in two different solvents to describe the effect of solvation and conformational motions on the rate of energy transfer. Moreover, we develop a fully dynamical model, based on Monte Carlo method, to analyze the characteristic timescales of such processes and compare them with the experimental picture. In Chapter 2 we examine spectroscopic properties of molecular aggregates, testing new approaches and approximation schemes for polar and non-polar supramolecular assemblies. The first part is focused on the discussion of aggregates of polar and polarizable dyes, improving already existent models to account for vibrational coupling and hence for spectral band-shapes. We then turn attention to aggregates of non-polar chromophores, addressing the reliability of the Heitler-London approximation and presenting a model for two dimensional aggregates. Chapters 3 and 4 are focused on chiral aggregates. In Chapter 3 we investigate aggregates formed by dicyanostilbenes decorated with chiral pendants. Through the use of an hybrid approach, involving MD simulations and exciton modeling, we are able to get a deep understanding on both aggregation and spectroscopic features of these system, questioning the effectiveness of widely adopted rules to assess the system chirality from Circular Dichroism (CD) spectra. In Chapter 4 we focus attention on non-symmetric squaraine aggregates. An extensive theoretical work is discussed, devoted to the study of spectroscopic features of squaraine assemblies in solution. We present a new model for the calculation of absorption and CD spectra of squaraine complexes using a delocalized electrons approach, taking into account for both intra- and intermolecular charge transfer mechanisms.