Results - Details
Search command : Author="Άγγλος"
And Author="Δημήτριος"
Current Record: 14 of 51
|
|
| Identifier |
000441496 |
| Title |
Υπερταχεία χρονοαναλυόμενη φασματοσκοπία απορρόφησης πορφυρινικών διεγμάτων με εφαρμογή την καταλυτική παραγωγή υδρογόνου |
| Alternative Title |
Ultrafast time - resolved absorption spectroscopy in porphyrins with application in catalytic hydrogen production |
|
Author
|
Πηγιάκη, Μαρία Ν.
|
|
Thesis advisor
|
Κουτσολέλος, Αθανάσιος
|
|
Reviewer
|
Άγγλος, Δημήτριος
Λουκάκος, Παναγιώτης
|
| Abstract |
In the context of this research, a study was carried out by use of ultrafast time–resolved absorption spectroscopy aiming to follow in detail the dynamics of photophysical processes in Zinc(II) tetraphenylporphyrin (ZnTPP) and a porphyrin-based hydrogen production system Sn(IV)–3PyP-FF-OMe–Co(dmgH2)pyCl. Solutions of the porphyrin systems were irradiated by ultra-short laser pulses (50 femtoseconds – fs) at λexc = 395 nm. Excitation of the chromophores populated instantly the upper vibrational levels of the second excited state (S2) and triggered a cascade of photophysical processes monitored in time by recording absorbance changes (ΔΑ) in the spectral range 420 – 730 nm. ZnTPP, a well studied porphyrin was chosen as a reference chromophore and the time resolved spectra collected helped to clarify key photophysical processes in porphyrins and facilitated optimization of the experimental setup. Analysis of the transient absorption spectra, along a time window as wide as 1 nanosecond (ns), led t,o identification of three distinct dynamic processes of ZnTPP, coupled to the following transitions: S0→S2 (λprobe = 426 nm), S0→S1 (λprobe = 555 nm), T1→Tn, S1→S2m and S2→Sx (λprobe= 430 – 520 nm). The characteristic life times measured were found to be in agreement with literature reports, giving characteristic times on the order of picoseconds (~2×10-12 s = 2 ps), for processes starting from S2, and in the nanosecond regime (t > 1 ×10-9 s = 1 ns) for processes starting from S1. The porphyrin Sn(IV)–3PyP-FF-OMe presented similar dynamic and spectral behavior as ZnTPP. The addition of cobaloxime in the solution drastically affects the dynamics observed at λprobe = 453 nm, and a fast decrease of the differential absorbance was observed for the porphyrin-cobaloxime sample, corresponding to a decay time of τ = 74 × 10-12 s. This dynamic behavior was attributed to electron transfer from the T1 state of the porphyrin to the cobaloxime moiety, Co(dmgH2)pyCl. It is noted that, in contrast, the dynamics of Sn (IV) - 3PyP-FF-OMe, in the absence of cobaloxime, indicated a slowly changing and even slightly increasing differential absorbance. Across the spectral window probed, 422 - 735 nm, no profound ΔA signals were observed that would indicate production of a charge transfer product, yet some weak features in the range of 650 – 700 nm might be attributed to an intermediate forming as a result of electron transfer.
|
| Language |
Greek |
| Subject |
Catalysis |
|
Donor – acceptor porphyrin systems |
|
Dynamics |
|
Electron transfer |
|
Κατάλυση |
|
Κινητική μοριακών συστημάτων |
|
Μεταφορά ηλεκτρονίου |
|
Πορφυρίνες |
|
Πορφυρινικά συστήματα δότη – δέκτη |
| Issue date |
2021-07-30 |
| Collection
|
School/Department--School of Sciences and Engineering--Department of Chemistry--Post-graduate theses
|
|
|
Type of Work--Post-graduate theses
|
| Permanent Link |
https://elocus.lib.uoc.gr//dlib/6/a/6/metadata-dlib-1627554189-75875-28699.tkl
|
| Views |
355 |
Search
