In recent years, squaraine dyes have garnered significant attention for their role in solution-processed photovoltaics due to their strong absorption in the red and near-infrared (NIR) region of the solar spectrum, which is not effectively harnessed by current technologies. Despite extensive experimental work and proposed applications, understanding the complex photophysics of these organic molecules, particularly in the ultrafast regime, remains limited. This Thesis aims to provide a deeper understanding of the static and time-resolved photophysical properties of three commercially available squaraines: 2,4-bis[4-(N,N-diisobutylamino)-2,6-dihydroxyphenyl] squaraine(SQ), 2,4-bis[4-(N,N-diphenylamino)-2,6-dihydroxyphenyl] squaraine (DPSQ), 2,4-bis[4-(N,N-dibenzylamino)-2,6-dihydroxyphenyl] squaraine (DBSQ). A combination of linear and nonlinear, static, and time-resolved optical spectroscopies was employed to investigate the origin of nonradiative decay pathways that might negatively affect the efficiency of these dyes as sensitizers for solar cells. In particular, we focused on the results obtained by applying two-dimensional electronic spectroscopy (2DES), which has proven to be well-suited for studying the ultrafast dynamics of squaraine dyes. This technique enabled the detailed examination of processes occurring on the femtosecond timescale and facilitated the determination of the time constants associated with various relaxation pathways in squaraine solutions. The obtained experimental results revealed the presence of a conical intersection (CI) between the ground and the excited state, as highlighted by distinct spectral signatures that could be explained by a two-state two-mode model. The crucial role of at least two vibrational modes strongly coupled with the electronic degrees of freedom has been elucidated. The passage through a CI was identified as a crucial relaxation pathway for the excited state, shedding light on one of the factors contributing to the complexity of the photophysical behavior of these dyes.
Signatures of Conical Intersections in Two-dimensional Electronic Spectra of Red-absorbing Squaraine Dyes
BURIGANA, VITTORIA
2023/2024
Abstract
In recent years, squaraine dyes have garnered significant attention for their role in solution-processed photovoltaics due to their strong absorption in the red and near-infrared (NIR) region of the solar spectrum, which is not effectively harnessed by current technologies. Despite extensive experimental work and proposed applications, understanding the complex photophysics of these organic molecules, particularly in the ultrafast regime, remains limited. This Thesis aims to provide a deeper understanding of the static and time-resolved photophysical properties of three commercially available squaraines: 2,4-bis[4-(N,N-diisobutylamino)-2,6-dihydroxyphenyl] squaraine(SQ), 2,4-bis[4-(N,N-diphenylamino)-2,6-dihydroxyphenyl] squaraine (DPSQ), 2,4-bis[4-(N,N-dibenzylamino)-2,6-dihydroxyphenyl] squaraine (DBSQ). A combination of linear and nonlinear, static, and time-resolved optical spectroscopies was employed to investigate the origin of nonradiative decay pathways that might negatively affect the efficiency of these dyes as sensitizers for solar cells. In particular, we focused on the results obtained by applying two-dimensional electronic spectroscopy (2DES), which has proven to be well-suited for studying the ultrafast dynamics of squaraine dyes. This technique enabled the detailed examination of processes occurring on the femtosecond timescale and facilitated the determination of the time constants associated with various relaxation pathways in squaraine solutions. The obtained experimental results revealed the presence of a conical intersection (CI) between the ground and the excited state, as highlighted by distinct spectral signatures that could be explained by a two-state two-mode model. The crucial role of at least two vibrational modes strongly coupled with the electronic degrees of freedom has been elucidated. The passage through a CI was identified as a crucial relaxation pathway for the excited state, shedding light on one of the factors contributing to the complexity of the photophysical behavior of these dyes.File | Dimensione | Formato | |
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https://hdl.handle.net/20.500.12608/80292