Nanographenes are promising nanostructure that can be engineered and design to tailor their properties for a specific use. The confinement of graphene within a few nanometers has led to the creation of a finite band gap in its electronic structure. This development opened for nanographenes a variety of applications with promising results \cite{DBOV2018paterno}. This Thesis focuses on Dibenzo[hi,st]ovalene molecule functionalized with two mesityl groups and two chlorine atoms (DBOVMes-Cl). The study focuses on its optoelectronic properties and on the interplay between electronic photo-excitation and vibrational degree of freedom. Such analysis was made possible by advance ultrafast spectroscopy techniques. Two-dimensional electron spectroscopy (2DES) emerges as a powerful time-resolved spectroscopical tool, offering high temporal and frequency resolution. The modeling of the experiment and its simulation were contextually developed allowing conjectures about the origin and role of molecular excited and ground state vibrations. The Brownian oscillator model and the displaced oscillator model were merged and applied to a two levels system to simulate a full 2DES dataset. The simulation were able to predict the lineshape evolution and the signal dynamics so that the defining physical quantities could be inferred from the model parameters. Additionally the presented evidences argue for a greater involvement of the excited state to the vibrational mode in the respect to the ground state. This can have profound implications in processes like energy and charges transfer within the molecule.
I nanografeni sono promettenti nanostrutture che possono essere progettate e ingegnerizzate per adattare le loro proprietà a un uso specifico. Il confinamento del grafene entro pochi nanometri ha portato alla creazione di salti energetici finiti nella sua struttura elettronica. Questo sviluppo ha aperto per i nanografeni numerose applicazioni con risultati promettenti \cite{DBOV2018paterno}. Questa tesi si concentra sulla molecola di Dibenzo[hi,st]ovalene funzionalizzata con due gruppi mesitili e due atomi di cloro (DBOVMes-Cl). Lo studio si concentra sulle sue proprietà optoelettroniche e sull'interazione tra foto-eccitazione elettronica e gradi di libertà vibrazionali. Tale analisi è stata resa possibile da tecniche avanzate di spettroscopia ultra-rapida. La spettroscopia elettronica bidimensionale (2DES) emerge come un potente strumento spettroscopico a tempo risolto, offrendo un'elevata risoluzione temporale e frequenziale. La modellizzazione dell'esperimento e la sua simulazione sono state sviluppate contestualmente, consentendo congetture sull'origine e sul ruolo delle vibrazioni molecolari negli stati eccitati e fondamentali. Il modello a oscillatori browniano e il modello a displaced oscillators sono stati applicati contemporaneamente a un sistema a due livelli per simulare un set di dati 2DES. Le simulazioni sono state in grado di predire l'evoluzione dello spettro 2D e la dinamica del segnale in modo che le quantità fisiche rilevanti potessero essere dedotte dai parametri del modello. Inoltre, le evidenze presentate sostengono un maggiore coinvolgimento nei modi vibrazionali dello stato eccitato rispetto rispetto allo stato fondamentale. Ciò può avere profonde implicazioni in processi come il trasferimento di energia e cariche all'interno della molecola.
Two dimensional electron spectroscopy of graphene nanoribbons: modeling and experiment
BASSI, GIACOMO
2022/2023
Abstract
Nanographenes are promising nanostructure that can be engineered and design to tailor their properties for a specific use. The confinement of graphene within a few nanometers has led to the creation of a finite band gap in its electronic structure. This development opened for nanographenes a variety of applications with promising results \cite{DBOV2018paterno}. This Thesis focuses on Dibenzo[hi,st]ovalene molecule functionalized with two mesityl groups and two chlorine atoms (DBOVMes-Cl). The study focuses on its optoelectronic properties and on the interplay between electronic photo-excitation and vibrational degree of freedom. Such analysis was made possible by advance ultrafast spectroscopy techniques. Two-dimensional electron spectroscopy (2DES) emerges as a powerful time-resolved spectroscopical tool, offering high temporal and frequency resolution. The modeling of the experiment and its simulation were contextually developed allowing conjectures about the origin and role of molecular excited and ground state vibrations. The Brownian oscillator model and the displaced oscillator model were merged and applied to a two levels system to simulate a full 2DES dataset. The simulation were able to predict the lineshape evolution and the signal dynamics so that the defining physical quantities could be inferred from the model parameters. Additionally the presented evidences argue for a greater involvement of the excited state to the vibrational mode in the respect to the ground state. This can have profound implications in processes like energy and charges transfer within the molecule.File | Dimensione | Formato | |
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G_Bassi_Thesis.pdf
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G_Bassi_Executive_Summary.pdf
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https://hdl.handle.net/10589/215876