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Asadinamin M, Živkovic A, Ullrich S, Meyer H, Zhao Y. Charge Dynamics of a CuO Thin Film on Picosecond to Microsecond Timescales Revealed by Transient Absorption Spectroscopy. ACS Appl Mater Interfaces 2023; 15:18414-18426. [PMID: 36995362 PMCID: PMC10103062 DOI: 10.1021/acsami.2c22595] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/15/2022] [Accepted: 03/21/2023] [Indexed: 06/19/2023]
Abstract
Understanding the mechanism of charge dynamics in photocatalysts is the key to design and optimize more efficient materials for renewable energy applications. In this study, the charge dynamics of a CuO thin film are unraveled via transient absorption spectroscopy (TAS) on the picosecond to microsecond timescale for three different excitation energies, i.e., above, near, and below the band gap, to explore the role of incoherent broadband light sources. The shape of the ps-TAS spectra changes with the delay time, while that of the ns-TAS spectra is invariant for all the excitation energies. Regardless of the excitations, three time constants, τ1 ∼ 0.34-0.59 ps, τ2 ∼ 162-175 ns, and τ3 ∼ 2.5-3.3 μs, are resolved, indicating the dominating charge dynamics at very different timescales. Based on these observations, the UV-vis absorption spectrum, and previous findings in the literature, a compelling transition energy diagram is proposed. Two conduction bands and two defect (deep and shallow) states dominate the initial photo-induced electron transitions, and a sub-valence band energy state is involved in the subsequent transient absorption. By solving the rate equations for the pump-induced population dynamics and implementing the assumed Lorentzian absorption spectral shape between two energy states, the TAS spectra are modeled which capture the main spectral and time-dependent features for t > 1 ps. By further considering the contributions from free-electron absorption during very early delay times, the modeled spectra reproduce the experimental spectra very well over the entire time range and under different excitation conditions.
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Affiliation(s)
- Mona Asadinamin
- Department
of Physics and Astronomy, University of
Georgia, Athens, Georgia 30602, United States
| | - Aleksandar Živkovic
- Department
of Earth Sciences, Utrecht University, Princetonlaan 8a, 3548 CB Utrecht, The Netherlands
| | - Susanne Ullrich
- Department
of Physics and Astronomy, University of
Georgia, Athens, Georgia 30602, United States
| | - Henning Meyer
- Department
of Physics and Astronomy, University of
Georgia, Athens, Georgia 30602, United States
| | - Yiping Zhao
- Department
of Physics and Astronomy, University of
Georgia, Athens, Georgia 30602, United States
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Hanna L, Movsesian E, Orozco M, Bernot AR, Asadinamin M, Shenje L, Ullrich S, Zhao Y, Marshall N, Weeks JA, Thomas MB, Teprovich JA, Ward PA. Spectroscopic investigation of the electronic and excited state properties of para-substituted tetraphenyl porphyrins and their electrochemically generated ions. Spectrochim Acta A Mol Biomol Spectrosc 2022; 278:121300. [PMID: 35512525 DOI: 10.1016/j.saa.2022.121300] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/04/2022] [Revised: 04/20/2022] [Accepted: 04/22/2022] [Indexed: 06/14/2023]
Abstract
Porphyrins play pivotal roles in many crucial biological processes including photosynthesis. However, there is still a knowledge gap in understanding electronic and excited state implications associated with functionalization of the porphyrin ring system. These effects can have electrochemical and spectroscopic signatures that reveal the complex nature of these somewhat minor substitutions, beyond simple inductive or electronic effect correlations. To obtain a deeper insight into the influences of porphyrin functionalization, four free-base, meso-substituted porphyrins: tetraphenyl porphyrin (TPP), tetra(4-hydroxyphenyl) porphyrin (THPP), tetra(4-carboxyphenyl) porphyrin (TCPP), and tetra(4-nitrophenyl) porphyrin (TNPP), were synthesized, characterized, and investigated. The influence of various substituents, (-hydroxy,-carboxy, and -nitro) in the para position of the meso-substituted phenyl moieties were evaluated by spectroelectrochemical techniques (absorption and fluorescence), femtosecond transient absorption spectroscopy, cyclic and differential pulse voltammetry, ultraviolet photoelectron spectroscopy (UPS), and time-dependent density functional theory (TD-DFT). Spectral features were evaluated for the neutral porphyrins and differences observed among the various porphyrins were further explained using rendered frontier molecular orbitals pertaining to the relevant transitions. Electrochemically generated anionic and cationic porphyrin species indicate similar absorbance spectroscopic signatures attributed to a red-shift in the Soret band. Emissive behavior reveals the emergence of one new fluorescence decay pathway for the ionic porphyrin, distinct from the neutral macrocycle. Femtosecond transient absorption spectroscopy analysis provided further analysis of the implications on the excited-state as a function of the para substituent of the free-base meso-substituted tetraphenyl porphyrins. Herein, we provide an in-depth and comprehensive analysis of the electronic and excited state effects associated with systematically varying the induced dipole at the methine bridge of the free-base porphyrin macrocycle and the spectroscopic signatures related to the neutral, anionic, and cationic species of these porphyrins.
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Affiliation(s)
- Lauren Hanna
- Advanced Manufacturing and Energy Science, Savannah River National Laboratory, Aiken, SC 29803, USA
| | - Edgar Movsesian
- Department of Chemistry and Biochemistry, California State University Northridge, 18111 Nordhoff St., Northridge, CA 91330, USA
| | - Miguel Orozco
- Department of Chemistry and Biochemistry, California State University Northridge, 18111 Nordhoff St., Northridge, CA 91330, USA
| | - Anthony R Bernot
- Department of Chemistry and Biochemistry, California State University Northridge, 18111 Nordhoff St., Northridge, CA 91330, USA
| | - Mona Asadinamin
- Department of Physics and Astronomy, University of Georgia Athens, GA, USA
| | - Learnmore Shenje
- Department of Physics and Astronomy, University of Georgia Athens, GA, USA
| | - Susanne Ullrich
- Department of Physics and Astronomy, University of Georgia Athens, GA, USA
| | - Yiping Zhao
- Department of Physics and Astronomy, University of Georgia Athens, GA, USA
| | - Nicholas Marshall
- Department of Chemistry and Physics, University of South Carolina-Aiken Aiken, SC, USA
| | - Jason A Weeks
- College of Natural Sciences, University of Texas Austin, Austin, TX, USA
| | - Michael B Thomas
- Advanced Manufacturing and Energy Science, Savannah River National Laboratory, Aiken, SC 29803, USA
| | - Joseph A Teprovich
- Department of Chemistry and Biochemistry, California State University Northridge, 18111 Nordhoff St., Northridge, CA 91330, USA.
| | - Patrick A Ward
- Advanced Manufacturing and Energy Science, Savannah River National Laboratory, Aiken, SC 29803, USA.
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Bradley L, Lin X, Chen Y, Asadinamin M, Ai B, Zhao Y. Janus Particles with Flower-like Patches Prepared by Shadow Sphere Lithography. Langmuir 2021; 37:13637-13644. [PMID: 34661420 DOI: 10.1021/acs.langmuir.1c02155] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
A general strategy for generating various Janus particles (JPs) based on shadow sphere lithography (SSL) by varying incident and azimuthal angles, as well as deposition numbers is introduced, forming well-identified flower-like patches on microsphere monolayers. An in-house simulation program is worked out to predict the patch morphology with complicated fabrication parameters. The predicted patch morphology matches quite well that of experimentally produced JPs. The relationships between patch shape/area/size/and incident angle/deposition numbers are quantitatively determined by calculating morphology and transmission spectrum correlations, which facilitated further implementation of SSL in fabricating more varieties of JPs. Such an SSL strategy can be used to create JPs with anticipated patch morphology and uniformity that may be used for self-assembly, drug delivery, or plasmonic sensors as well as exploring some fundamental principles relating to the properties of nanostructures.
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Affiliation(s)
- Layne Bradley
- Department of Physics and Astronomy, University of Georgia, Athens, Georgia 30602, United States
| | - Xiangxin Lin
- School of Microelectronics and Communication Engineering, Chongqing University, Chongqing 400044, P.R. China
| | - Yanjun Chen
- School of Microelectronics and Communication Engineering, Chongqing University, Chongqing 400044, P.R. China
| | - Mona Asadinamin
- Department of Physics and Astronomy, University of Georgia, Athens, Georgia 30602, United States
| | - Bin Ai
- School of Microelectronics and Communication Engineering, Chongqing University, Chongqing 400044, P.R. China
- Chongqing Key Laboratory of Bio-perception & Intelligent Information Processing, Chongqing 400044, P.R. China
| | - Yiping Zhao
- Department of Physics and Astronomy, University of Georgia, Athens, Georgia 30602, United States
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