Petrone, Alessio (2014) Theoretical study of time resolved spectroscopy and non-equilibrium processes. [Tesi di dottorato]


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Item Type: Tesi di dottorato
Lingua: English
Title: Theoretical study of time resolved spectroscopy and non-equilibrium processes
Date: 28 March 2014
Number of Pages: 156
Institution: Università degli Studi di Napoli Federico II
Department: Scienze Chimiche
Scuola di dottorato: Scienze chimiche
Dottorato: Scienze chimiche
Ciclo di dottorato: 26
Coordinatore del Corso di dottorato:
Date: 28 March 2014
Number of Pages: 156
Uncontrolled Keywords: Theory, Dynamics, Non-equilibrium
Settori scientifico-disciplinari del MIUR: Area 03 - Scienze chimiche > CHIM/02 - Chimica fisica
Date Deposited: 10 Apr 2014 08:09
Last Modified: 15 Jul 2015 01:01


We developed new theoretical models and computational tools to explore the dynamical behavior of several systems, mostly in the biological field, undergoing nonequilibrium process or time-resolved spectroscopy. We focused our attention on the cutting edge challenges of the modern theoretical and computational chemistry, without ever neglecting the experimental implications. In fact, we can easily say that our challenges share the same attention in both the theoretical chemistry and the modern and newest experimental and technological applications, such as the newest time-resolved spectroscopies, the solar cell device design, innovative protein-based bio-sensors. The common, and in our opinion intriguing, factors of our work are the following: the molecular dynamics, the characterization of electronic excited states, and the modeling of complex events. Therefore, in each phase of the project we designed our theory and our computational experiments by studying our cases as a dynamic embedded system, surrounded by its environment, describing its excited electronic states and its temporal evolution. Moreover, the time dependence of our results provided an additional trigger to develop also new, or more accurate, tools of analysis. Three different case studies are presented, facing different experimental issues affecting different and shorter and shorter time scales. First, the N-methyl-6-oxyquinolinium betaine time resolved Stokes-Shift experiment in water solution was investigated. Nowadays, thanks to the ultra-fast pulsed laser techniques, we are able to freeze the far-from-equilibrium structures during a molecular vibration or a reaction. We proposed a new computational protocol to study the excited state dynamics ruling the non equilibrium relaxation process affecting a fluorescent probe upon the electronic excitation. In this work, we explained how the whole time dependent signal is influenced in a dynamical way by several collective solvent motions. After we presented several theoretical tools to characterize the behavior of transient excited states within bio-macromolecules. In particular we focused our efforts to study the excited state photo-reactivity and the optical behavior of the Green Fluorescent Protein (GFP). We calculate at the same level of TD-DFT the vertical excitation energy of the anionic GFP chromophore in the protein and in ethanol, dioxane, methanol and water solutions. As result, we reproduced for the first time the experimental trend of the absorption peaks with 0.015 eV as standard deviation of the accuracy. During this work, we also contributed to the tangled debate on the gas-phase GFP chromophore experimental reference absorption value. Moreover, the Excited State Proton Transfer in the GFP is a complex and fascinating event of a paramount importance in many scientific and technological fields. Therefore, we also proposed an innovative computational protocol to face the simulation of a complex non-equilibrium process, such as the photo-reactivity affecting the GFP, going from easier to more accurate modeling approaches, along with showing the nature of the mechanism and the complex role of the protein matrix on it. Finally, we explored the exciton dynamics of bulk hetero-junction (BHJ) based polymer solar cells. Therefore, we exploited a computational method that provides the explicit evolution of the electronic density along the time after the photon absorption, on sub-femto time scale. The innovative real-time non-adiabatic nonperturbative TDDFT electronic dynamics was used to better understand the interplay between the photo-excited electron-hole pair and the charge separated state. This work gave us an useful molecular insight for BHJ based polymer solar cell design, showing the crucial role of theoretical chemistry to investigate how small modifications on molecular scale can influence the properties of the whole device.

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