Periodic Reporting for period 3 - TOMATTO (The ultimate Time scale in Organic Molecular opto-electronics, the ATTOsecond)
Berichtszeitraum: 2024-04-01 bis 2025-09-30
Photoinduced electron transfer (ET) and charge transfer (CT) processes occurring in organic materials are the cornerstone of technologies aiming at the conversion of solar energy into electrical energy and at its efficient transport. Thus, investigations of ET/CT induced by visible (VIS) and ultraviolet (UV) light are fundamental for the development of more efficient organic opto-electronic materials. The usual strategy to improve efficiency is chemical modification, which is based on chemical intuition and trial-and-error approaches, with no control on the ultrafast electron dynamics induced by light. Achieving the latter is not easy, as the natural time scale for electronic motion is the attosecond (10-18 seconds). In this project we propose to overcome the current time-scale bottleneck and get direct information on the early stages of ET/CT generated by VIS and UV light absorption on organic opto-electronic systems by extending the tools of attosecond science beyond the state of the art and combining them with the most advanced methods of organic synthesis and computational modelling. The objective is to provide clear-cut movies of ET/CT with unprecedented time resolution and with the ultimate goal of engineering the molecular response to optimize the light driven processes leading to the desired opto-electronic behaviour.
1. Attosecond XUV-pump/IR-probe measurements were conducted on several gas-phase donor-acceptor systems, namely, nitroanilines and biphenyl derivatives. The results were interpreted by means of state-of-the art theoretical calculations. We found that CT can be much faster than anticipated (~10 fs) and even reversible. We also performed measurements in C60 and observed time delays of approximately 300 attoseconds, attributed to electron correlation effects associated with plasmonic resonances.
2. A beamline for soft X-ray generation has been developed, driven by IR pulses with durations down to ~10 fs and tunable wavelengths in the 1.1–2.6 µm range.
3. Ultrashort deep-UV (DUV) and UV pulses tuneable within the 200–350 nm spectral range have been generated using the resonant dispersive wave (RDW) emission process. The minimum pulse duration achieved is 2.4 fs.
4. An attosecond UV-pump/XUV-probe beamline has been implemented with active stabilization of the pump–probe delay. First time-resolved UV-XUV measurements validated a ~3-fs instrumental response via cross-correlation in argon.
5. Time dependent versions of XCHEM and esx-DFT have been developed from the existing time-independent versions. For diatomic and triatomic molecules, the effect of nuclear motion and the coupling of this motion with the electronic one were described in a full quantum mechanical way.
6. A new theoretical method, PFM-TSH, has been developed and successfully tested to properly account for the evolution of the electronic coherences created by few-fs UV pulses in the framework of a classical trajectory approach, which is the only one feasible for large molecules.
7. Time-resolved UV-pump/XUV-probe experiments with ~3-fs time resolution were performed on gas-phase pyrazine and isopropoxy-nitrobenzene. For pyrazine, theoretical calculations using the newly developed computational methods have provided time-resolved photoelectron spectra directly comparable with the experimental ones.
8. Theoretical identification of Graphene/SiC as an ideal substrate for deposition of organic molecules without destroying their donor-acceptor character while keeping them firmly bonded to the substrate.
9. Enantioselective synthesis of molecular nanographenes has been carried out for the first time, thus avoiding the use of expensive and time-consuming HPLC chromatography and paving the way to the preparation of these materials in gram amounts for practical applications.
2. A beamline for soft X-ray generation has been developed, driven by IR pulses with durations down to ~10 fs and tunable wavelengths in the 1.1–2.6 µm range.
3. Ultrashort deep-UV (DUV) and UV pulses tuneable within the 200–350 nm spectral range have been generated using the resonant dispersive wave (RDW) emission process. The minimum pulse duration achieved is 2.4 fs.
4. An attosecond UV-pump/XUV-probe beamline has been implemented with active stabilization of the pump–probe delay. First time-resolved UV-XUV measurements validated a ~3-fs instrumental response via cross-correlation in argon.
5. Time dependent versions of XCHEM and esx-DFT have been developed from the existing time-independent versions. For diatomic and triatomic molecules, the effect of nuclear motion and the coupling of this motion with the electronic one were described in a full quantum mechanical way.
6. A new theoretical method, PFM-TSH, has been developed and successfully tested to properly account for the evolution of the electronic coherences created by few-fs UV pulses in the framework of a classical trajectory approach, which is the only one feasible for large molecules.
7. Time-resolved UV-pump/XUV-probe experiments with ~3-fs time resolution were performed on gas-phase pyrazine and isopropoxy-nitrobenzene. For pyrazine, theoretical calculations using the newly developed computational methods have provided time-resolved photoelectron spectra directly comparable with the experimental ones.
8. Theoretical identification of Graphene/SiC as an ideal substrate for deposition of organic molecules without destroying their donor-acceptor character while keeping them firmly bonded to the substrate.
9. Enantioselective synthesis of molecular nanographenes has been carried out for the first time, thus avoiding the use of expensive and time-consuming HPLC chromatography and paving the way to the preparation of these materials in gram amounts for practical applications.
We have developed an advanced attosecond beamline that features a combination of capabilities currently unmatched in the international research landscape. The setup is designed to perform time-resolved pump–probe experiments with exceptional temporal resolution and spectral flexibility. It is based on the use of excitation pulses tuneable over a broad spectral range in the deep-UV (DUV)/UV region, with durations below 3 femtoseconds and pulse energies of several hundred nanojoules at the target. The probe pulses, in the XUV spectral region, feature sub-femtosecond durations. Initial pump–probe experiments have been successfully conducted on prototype molecular systems in the gas phase, demonstrating the beamline capability to capture electron and nuclear dynamics occurring on few-femtosecond and sub-femtosecond timescales. This beamline will serve as a core tool throughout the project, enabling the investigation of ultrafast processes in a broad range of molecular structures of relevance to optoelectronics.
We have developed a new theoretical method, the projected forces and momentum trajectory surface hoping (PFM-TSH) method, to properly account for the initial coherent superposition of electronic states generated by 2-3 fs UV pump pulses. The method has been successfully checked by explicitly comparing with the results of full quantum mechanical calculations in small and medium-size molecules. It will allow us to describe the coupled electron and nuclear dynamics arising from such coherent superposition.
In addition to the design and synthesis of the appropriate molecules for determining smart electron dynamics, the generation of unprecedented molecular donor-acceptor bilayer nanographenes should be appealing systems for studying the electron dynamics through empty space. This could be a fundamental study for addressing other challenging advanced systems.
We have developed a new theoretical method, the projected forces and momentum trajectory surface hoping (PFM-TSH) method, to properly account for the initial coherent superposition of electronic states generated by 2-3 fs UV pump pulses. The method has been successfully checked by explicitly comparing with the results of full quantum mechanical calculations in small and medium-size molecules. It will allow us to describe the coupled electron and nuclear dynamics arising from such coherent superposition.
In addition to the design and synthesis of the appropriate molecules for determining smart electron dynamics, the generation of unprecedented molecular donor-acceptor bilayer nanographenes should be appealing systems for studying the electron dynamics through empty space. This could be a fundamental study for addressing other challenging advanced systems.