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Papers by Amani Alsam

International Journal of Electrochemical Science, Mar 1, 2024

Molecules/Molecules online/Molecules annual, Jan 29, 2024

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Biomedical Chromatography, Dec 3, 2023

Journal of physical chemistry. C./Journal of physical chemistry. C, Jun 17, 2024

Photophysical Characterization of Donors-Acceptor Systems using Ultrafast Laser Spectroscopy Aman... more Photophysical Characterization of Donors-Acceptor Systems using Ultrafast Laser Spectroscopy Amani Abdu M Alsam In donor-acceptor systems, ultrafast interfacial charge transfer (CT), charge separation (CS) and charge recombination (CR), are among the key factors in determining the overall efficiency of the optoelectronic devices. In this regime, precise knowledge of the mechanisms of these processes on the femtosecond scale is urgently required. In this dissertation, using femtosecond transient absorption and mid-Infrared spectroscopies along with steady-state absorption and emission measurements, we are not only able to address the fundamental understanding of these ultrafast dynamical processes, but also control them at various interand intramolecular electron donor-electron acceptor systems. In the photoinduced intermolecular charge transfer systems, where donor and acceptor are separated from each other, three systems have been investigated; cationic poly[(9,9-di(3,3′N,N′-trimet...

The Journal of Physical Chemistry C, 2017

Controlling the ultrafast dynamical process of photoinduced charge-transfer at donor-acceptor int... more Controlling the ultrafast dynamical process of photoinduced charge-transfer at donor-acceptor interfaces remains a major challenge for physical chemistry and solar cell communities. The process is complicated by the involvement of other complex dynamical processes, including hydrogen bond formation, energy transfer and solvation dynamics occurring on similar time scales. In this study, we explore the remarkable impact of hydrogen-bond formation on the interfacial charge transfer between a negatively charged electron donating anionic porphyrin and a positively charged electron accepting -conjugated polymer, as a model system in solvents with different polarities and capabilities for hydrogen bonding using femtosecond transient absorption spectroscopy. Unlike the conventional understanding of the key role of hydrogen bonding in promoting the charge transfer process, our steady-state and timeresolved results reveal that the intervening hydrogen-bonding environment and consequently the probable longer spacing between the donor and acceptor molecules significantly hinders the charge-transfer process between them. These results show that site-specific hydrogen bonding and geometric considerations between donor and acceptor can be exploited to control both the chargetransfer dynamics and its efficiency not only at donor-acceptor interfaces, but also in complex biological systems.

The journal of physical chemistry. A, Jan 25, 2017

A series of -conjugated oligomer-acceptor dyads were synthesized that feature oligo(phenylene eth... more A series of -conjugated oligomer-acceptor dyads were synthesized that feature oligo(phenylene ethynylene) (OPE) conjugated backbones end-capped with a naphthalene diimide (NDI) acceptor. The OPE segments vary in length from 4 to 8 phenylene ethynene units (PEn-NDI, where n = 4, 6 and 8). Fluorescence and transient absorption spectroscopy reveals that intramolecular OPE NDI charge transfer dominates the deactivation of excited states of the PEn-NDI oligomers. Both charge separation (CS) and charge recombination (CR) are strongly exothermic (G0CS ~ -1.1 and G0CR ~ -2.0 eV), and the driving forces do not vary much across the series because the oxidation and reduction potentials and singlet energies of the OPEs do not vary much with their length. Bimolecular photoinduced charge transfer between model OPEs that do not contain the NDI acceptors with methyl viologen was studied, and the results reveal that the absorption of the cation radical state (OPE+•) remains approximately constant ( ...

Light Manipulating Organic Materials and Devices III, 2016

Photoinduced charge transfer is a key step in the mechanism of charge generation in organic solar... more Photoinduced charge transfer is a key step in the mechanism of charge generation in organic solar cells. Charge transfer typically occurs from a photoexcited conjugated polymer donor to an electron acceptor. In an effort to better understand the primary events in solar cells, we have investigated photoinduced charge transfer in model donor-acceptor systems consisting of pi-conjugated oligomer donors that are covalently linked to diimide electron acceptors. These studies utilized oligo(thiophene), oligo(phenylene ethynylene) and oligo(fluorene) pi-conjugated systems with lengths varying from 4 to 12 repeat units linked to naphthalene diimide electron acceptors. Excitation with 100 femtosecond pulses at wavelengths correspoinding to the conjugated oligomer absorption band(s) leads to rapid photoinduced charge transfer to produce a charge separated state, (oligomer+)-(NDI-), which subsequently decays on timescales ranging from 100 ps to 5 ns. The dynamics of the forward and reverse electron transfer reactions depend strongly on the structure and length of the pi-conjugated oligomers, with the fastest rates occurring for oligo(thiophene)s, and considerably slower rates for oligo(phenylene ethynylene)s. The talk will discuss the structure-property relationships and energetic correlations that control the dynamics of charge separation and recombination.

Dyes and Pigments, 2017

OF, Real-time observation of intersystem crossing induced by charge recombination during bimolecu... more OF, Real-time observation of intersystem crossing induced by charge recombination during bimolecular electron transfer reactions, Dyes and Pigments (2016),

The Journal of Physical Chemistry C, 2015

We explored the excited-state interactions of bimolecular, non-covalent systems consisting of cat... more We explored the excited-state interactions of bimolecular, non-covalent systems consisting of cationic poly[(9,9-di(3,3'-N,N'-trimethyl-ammonium) propyl fluorenyl-2,7-diyl)-alt-co-(9,9dioctyl-fluorenyl-2,7-diyl)] diiodide salt (PFN) and 1,4-dicyanobenzene (DCB) using steadystate and time-resolved techniques, including femto-and nanosecond transient absorption and femtosecond infrared spectroscopies with broadband capabilities. The experimental results demonstrated that photo-induced electron transfer from PFN to DCB occurs on the picosecond time scale, leading to the formation of PFN +• and DCB-• radical ions. Interestingly, real-time observations of the vibrational marker modes on the acceptor side provided direct evidence and insight into the electron transfer process indirectly inferred from UV-Vis experiments. The band narrowing on the picosecond time scale observed on the antisymmetric C-N stretching vibration of the DCB radical anion provides clear experimental evidence that a substantial part of the excess energy is channeled into vibrational modes of the electron transfer product and that the geminate ion pairs dissociate. More importantly, our nanosecond time-resolved data indicate that the charge-separated state is very long lived (∼ 30 ns) due to the dissociation of the contact radical ion pair into free ions. Finally, the fast electron transfer and slow charge recombination anticipate the current donor−acceptor system with potential applications in organic solar cells.

The research presented in this thesis was focused on organic semiconductors and has resulted in t... more The research presented in this thesis was focused on organic semiconductors and has resulted in the development of novel printable polymer semiconductors that can be used in organic thin film transistors (OTFTs) and organic photovoltaics (OPVs), or solar cells. Polymers used in OTFT applications must have particular characteristics, such as a highly ordered or crystalline structure, favoured molecular orientation, and appropriate energy levels for either hole transport (p-type semiconductors) or electron transport (n-type semiconductors). Achieving these properties requires control of the design and synthesis of the polymers through the choice of appropriate building blocks and side chain substituents. In contrast, for OPV applications, the band gap, thin film morphology, and balance of the donor's hole mobility and the acceptor's electron mobility must be finely tuned for optimal photovoltaic performance. The specific focus of the research was on a new type of donor-acceptor copolymers that have alternating electronaccepting azo units and common electron donor units (e.g., thiophene). These polymers are expected to have strong intermolecular interactions due to the donor-acceptor effect, which could lead to improved molecular organization for efficient charge carrier transport in OTFT devices. The donor-acceptor effect also creates narrow band gap polymers, which are preferred for optimum light harvesting. The polymer materials developed in this research are evaluated as channel semiconductors in OTFTs and can also be used as donors in polymer solar cells. Zs discovery of which complemented previous work conducted by the same research group. These innovative building blocks would be valuable in numerous applications, including OTFTs and OPVs. Five polymers have been created, three of which show the most promising potential for OTFT and OPV applications: P1-DTA-BTV, P5-DTAE-BT, and P6-DTAE-TT. All of these copolymers have been synthesized via Stille coupling reaction. The first copolymer, P1-DTA-BTV, which exhibits a small band gap of 1.13 eV, with HOMO and LUMO energy levels of-5.21 eV and-4.08 eV, respectively, is suitable for both OTFT devices and OPV applications. P5-DTAE-BT and P6-DTAE-TT, on the other hand, are characterized by broader band gaps of 1.29 eV and 1.32 eV, respectively, and their average HOMO and LUMO energy levels are-5.43 eV,-4.20 eV, and-5.40 eV,-4.00 eV, respectively. It has been experimentally demonstrated that the presence of an ester group in the (E)-1,2-di(thiazol-2-yl)diazene DTA monomer helps lower the LUMO energy level, creating the broad band gap revealed in the (E)-bis(2-octyldodecyl) 2,2'-(diazene-1,2-diyl)bis(thiazole-4-carboxylate) DTAE copolymer results, and making the P5iv DTAE-BT D-A copolymer an n-type semiconductor, which is very useful for the applications mentioned above. The polymers were characterized by Differential Scanning Calorimetry DSC, Thermal Gravimetric Analysis TGA, Ultraviolet-Visible Spectrometry UV-Vis, Cyclic Voltammetry CV, Atomic Force Microscopy AFM, and X-Ray Diffraction XRD. v I would like to thank my supervisor, Professor Yuning Li, for his encouragement, guidance, and invaluable assistance during my studies. I would also like to express my gratitude to Wei Hong, Chang Guo, and Bin Sun for their help with the characterizations and device performance. Many thanks go to Jesse Quinn, who has had great contributions to some parts of this project and provided extensive assistance in the laboratory. I am likewise very appreciative of my review committee, Professor Neil McManus, and Professor Aiping Yu. A own particular gratitude to my parents specially my father, a natural giver, who encouraged me to complete my studies, as well as to my brothers, Majed and Fahad, who stood by me all the way through my study and challenges, endowing me with love, confidence, and unlimited support. I give heartfelt thanks for my family; to whom I owe more gratitude than I can ever put into words. Among my sincere acknowledgements, the financial support I have received from the Saudi Arabian Ministry of Higher Education is highly appreciated.