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Ficarra G, Sciortino A, Barbata LG, Ettlinger R, De Michele V, Marin E, Cannas M, Morris RE, Buscarino G. Unveiling MOF-808 photocycle and its interaction with luminescent guests. Phys Chem Chem Phys 2024; 26:22269-22277. [PMID: 39136117 DOI: 10.1039/d4cp02279c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/23/2024]
Abstract
The world of metal-organic frameworks (MOFs) has become a hot topic in recent years due to the extreme variety and tunability of their structures. There is evidence of MOFs that exhibit intrinsic luminescence properties that arise directly from their organic components or from the interaction between them and metallic counterparts. A new perspective is to exploit the porous nature of MOFs by encapsulating luminescent guests, such as organic dyes, in order to explore possible changes in the luminescence activity of the combined systems. This work is focused on the optical study of zirconium-based MOF-808 and its interaction with encapsulated rhodamine B molecules. Using a plethora of different techniques, we were able to unravel its photocycle. MOF-808 displays intrinsic luminescence activity that derives from an energy transfer process from the linker to the metal sites occurring in 300 ps. The emission is a singlet-singlet transition in aqueous solution, and it is a triplet transition in powdered form. After exploring the bare MOF, we combined it with rhodamine B molecules, following an easy post-synthetic process. Rhodamine B molecules were found to be encapsulated in MOF pores and interact with the MOF's matrix through nanosecond energy transfer. We created a totally new dual-emitting system and suggested a way, based on the time-resolved studies, to clearly unravel the photocycle of MOFs from the very first photoexcitation.
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Affiliation(s)
- G Ficarra
- Department of Physics and Chemistry "Emilio Segrè", University of Palermo, Via Archirafi 36, 90123 Palermo, Italy.
| | - A Sciortino
- Department of Physics and Chemistry "Emilio Segrè", University of Palermo, Via Archirafi 36, 90123 Palermo, Italy.
| | - L G Barbata
- Department of Physics and Chemistry "Emilio Segrè", University of Palermo, Via Archirafi 36, 90123 Palermo, Italy.
| | - R Ettlinger
- TUM School of Natural Sciences, Technical University of Munich Lichtenbergstr. 4, 85748 Garching b. München, Germany
| | - V De Michele
- Université Jean Monnet, CNRS, IOGS, Laboratoire Hubert Curien UMR 5516, 42000 Saint-Etienne, France
| | - E Marin
- Université Jean Monnet, CNRS, IOGS, Laboratoire Hubert Curien UMR 5516, 42000 Saint-Etienne, France
| | - M Cannas
- Department of Physics and Chemistry "Emilio Segrè", University of Palermo, Via Archirafi 36, 90123 Palermo, Italy.
| | - R E Morris
- EastChem School of Chemistry, University of St Andrews, North Haugh, St Andrews, UK
| | - G Buscarino
- Department of Physics and Chemistry "Emilio Segrè", University of Palermo, Via Archirafi 36, 90123 Palermo, Italy.
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2
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Cui E, Liu H, Wang Z, Chen H, Weng YX. Femtosecond fluorescence conical optical parametric amplification spectroscopy. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2024; 95:033008. [PMID: 38517256 DOI: 10.1063/5.0197254] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/12/2024] [Accepted: 02/29/2024] [Indexed: 03/23/2024]
Abstract
Parametric superfluorescence (PSF), which originated from the optical amplification of vacuum quantum noise, is the primary noise source of femtosecond fluorescence non-collinear optical parametric amplification spectroscopy (FNOPAS). It severely affects the detection limit of FNOPAS to collect the femtosecond time-resolved spectra of extremely weak fluorescence. Here, we report the development of femtosecond fluorescence conical optical parametric amplification spectroscopy (FCOPAS), aimed at effectively suppressing the noise fluctuation from the PSF background. In contrast to traditional FNOPAS configurations utilizing lateral fluorescence collection and dot-like parametric amplification, FCOPAS employs an innovative conical fluorescence collection and ring-like amplification setup. This design enables effective cancellation of noise fluctuation across the entire PSF ring, resulting in an approximate order of magnitude reduction in PSF noise compared to prior FNOPAS outcomes. This advancement enables the resolution of transient fluorescence spectra of 4-dicyanomethylene-2-methyl-6-p-dimethylaminostyryl-4H-pyran (DCM) dye molecules in ethanol, even at an optically dilute concentration of 10-6 mol/l, with significantly enhanced signal-to-noise ratios. This improvement will be significant for extremely weak fluorescence detection on the femtosecond time scale.
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Affiliation(s)
- Ennan Cui
- The Laboratory of Soft Matter Physics, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- School of Physical Science, University of the Chinese Academy of Sciences, Beijing 100049, China
| | - Heyuan Liu
- The Laboratory of Soft Matter Physics, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- School of Physical Science, University of the Chinese Academy of Sciences, Beijing 100049, China
| | - Zhuan Wang
- The Laboratory of Soft Matter Physics, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
| | - Hailong Chen
- The Laboratory of Soft Matter Physics, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- School of Physical Science, University of the Chinese Academy of Sciences, Beijing 100049, China
- Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China
| | - Yu-Xiang Weng
- The Laboratory of Soft Matter Physics, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- School of Physical Science, University of the Chinese Academy of Sciences, Beijing 100049, China
- Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China
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3
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Olla C, Cappai A, Porcu S, Stagi L, Fantauzzi M, Casula MF, Mocci F, Corpino R, Chiriu D, Ricci PC, Carbonaro CM. Exploring the Impact of Nitrogen Doping on the Optical Properties of Carbon Dots Synthesized from Citric Acid. NANOMATERIALS (BASEL, SWITZERLAND) 2023; 13:1344. [PMID: 37110929 PMCID: PMC10141696 DOI: 10.3390/nano13081344] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/23/2023] [Revised: 04/07/2023] [Accepted: 04/09/2023] [Indexed: 06/19/2023]
Abstract
The differences between bare carbon dots (CDs) and nitrogen-doped CDs synthesized from citric acid as a precursor are investigated, aiming at understanding the mechanisms of emission and the role of the doping atoms in shaping the optical properties. Despite their appealing emissive features, the origin of the peculiar excitation-dependent luminescence in doped CDs is still debated and intensively being examined. This study focuses on the identification of intrinsic and extrinsic emissive centers by using a multi-technique experimental approach and computational chemistry simulations. As compared to bare CDs, nitrogen doping causes the decrease in the relative content of O-containing functional groups and the formation of both N-related molecular and surface centers that enhance the quantum yield of the material. The optical analysis suggests that the main emission in undoped nanoparticles comes from low-efficient blue centers bonded to the carbogenic core, eventually with surface-attached carbonyl groups, the contribution in the green range being possibly related to larger aromatic domains. On the other hand, the emission features of N-doped CDs are mainly due to the presence of N-related molecules, with the computed absorption transitions calling for imidic rings fused to the carbogenic core as the potential structures for the emission in the green range.
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Affiliation(s)
- Chiara Olla
- Department of Physics, University of Cagliari, Cittadella Universitaria, I-09042 Monserrato, Italy
| | - Antonio Cappai
- Department of Physics, University of Cagliari, Cittadella Universitaria, I-09042 Monserrato, Italy
| | - Stefania Porcu
- Department of Physics, University of Cagliari, Cittadella Universitaria, I-09042 Monserrato, Italy
| | - Luigi Stagi
- Laboratory of Materials Science and Nanotechnology, CR-INSTM, Department of Chemical, Physics, Mathematics and Natural Sciences, University of Sassari, Via Vienna 2, 07100 Sassari, Italy
| | - Marzia Fantauzzi
- Department of Chemistry and Geological Science, University of Cagliari, Cittadella Universitaria, I-09042 Monserrato, Italy
| | - Maria Francesca Casula
- Department of Mechanical, Chemical, and Materials Engineering, CINSA and INSTM, University of Cagliari, Via Marengo 2, I-09123 Cagliari, Italy
| | - Francesca Mocci
- Department of Chemistry and Geological Science, University of Cagliari, Cittadella Universitaria, I-09042 Monserrato, Italy
| | - Riccardo Corpino
- Department of Physics, University of Cagliari, Cittadella Universitaria, I-09042 Monserrato, Italy
| | - Daniele Chiriu
- Department of Physics, University of Cagliari, Cittadella Universitaria, I-09042 Monserrato, Italy
| | - Pier Carlo Ricci
- Department of Physics, University of Cagliari, Cittadella Universitaria, I-09042 Monserrato, Italy
| | - Carlo Maria Carbonaro
- Department of Physics, University of Cagliari, Cittadella Universitaria, I-09042 Monserrato, Italy
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4
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Liang W, Sonkar SK, Saini D, Sheriff K, Singh B, Yang L, Wang P, Sun YP. Carbon Dots: Classically Defined versus Organic Hybrids on Shared Properties, Divergences, and Myths. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2023:e2206680. [PMID: 36932892 DOI: 10.1002/smll.202206680] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/29/2022] [Revised: 02/28/2023] [Indexed: 06/18/2023]
Abstract
Carbon dots are defined as small carbon nanoparticles with effective surface passivation via organic functionalization. The definition is literally a description of what carbon dots are originally found for the functionalized carbon nanoparticles displaying bright and colorful fluorescence emissions, mirroring those from similarly functionalized defects in carbon nanotubes. In literature more popular than classical carbon dots are the diverse variety of dot samples from "one-pot" carbonization of organic precursors. On the two different kinds of samples from the different synthetic approaches, namely, the classical carbon dots versus those from the carbonization method, highlighted in this article are their shared properties and apparent divergences, including also explorations of the relevant sample structural and mechanistic origins for the shared properties and divergences. Echoing the growing evidence and concerns in the carbon dots research community on the major presence of organic molecular dyes/chromophores in carbonization produced dot samples, demonstrated and discussed in this article are some representative cases of dominating spectroscopic interferences due to the organic dye contamination that have led to unfound claims and erroneous conclusions. Mitigation strategies to address the contamination issues, including especially the use of more vigorous processing conditions in the carbonization synthesis, are proposed and justified.
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Affiliation(s)
- Weixiong Liang
- Department of Chemistry, Clemson University, Clemson, SC, 29634, USA
| | - Sumit Kumar Sonkar
- Department of Chemistry, Malaviya National Institute of Technology, Jaipur, Rajasthan, 302017, India
| | - Deepika Saini
- Department of Chemistry, Malaviya National Institute of Technology, Jaipur, Rajasthan, 302017, India
| | - Kirkland Sheriff
- Department of Chemistry, Clemson University, Clemson, SC, 29634, USA
| | - Buta Singh
- Department of Chemistry, Clemson University, Clemson, SC, 29634, USA
| | - Liju Yang
- Department of Pharmaceutical Sciences, Biomanufacturing Research Institute and Technology Enterprise, North Carolina Central University, Durham, NC, 27707, USA
| | - Ping Wang
- Department of Chemistry, Clemson University, Clemson, SC, 29634, USA
| | - Ya-Ping Sun
- Department of Chemistry, Clemson University, Clemson, SC, 29634, USA
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5
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Mocci F, de Villiers Engelbrecht L, Olla C, Cappai A, Casula MF, Melis C, Stagi L, Laaksonen A, Carbonaro CM. Carbon Nanodots from an In Silico Perspective. Chem Rev 2022; 122:13709-13799. [PMID: 35948072 PMCID: PMC9413235 DOI: 10.1021/acs.chemrev.1c00864] [Citation(s) in RCA: 17] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Carbon nanodots (CNDs) are the latest and most shining rising stars among photoluminescent (PL) nanomaterials. These carbon-based surface-passivated nanostructures compete with other related PL materials, including traditional semiconductor quantum dots and organic dyes, with a long list of benefits and emerging applications. Advantages of CNDs include tunable inherent optical properties and high photostability, rich possibilities for surface functionalization and doping, dispersibility, low toxicity, and viable synthesis (top-down and bottom-up) from organic materials. CNDs can be applied to biomedicine including imaging and sensing, drug-delivery, photodynamic therapy, photocatalysis but also to energy harvesting in solar cells and as LEDs. More applications are reported continuously, making this already a research field of its own. Understanding of the properties of CNDs requires one to go to the levels of electrons, atoms, molecules, and nanostructures at different scales using modern molecular modeling and to correlate it tightly with experiments. This review highlights different in silico techniques and studies, from quantum chemistry to the mesoscale, with particular reference to carbon nanodots, carbonaceous nanoparticles whose structural and photophysical properties are not fully elucidated. The role of experimental investigation is also presented. Hereby, we hope to encourage the reader to investigate CNDs and to apply virtual chemistry to obtain further insights needed to customize these amazing systems for novel prospective applications.
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Affiliation(s)
- Francesca Mocci
- Department
of Chemical and Geological Sciences, University
of Cagliari, I-09042 Monserrato, Italy,
| | | | - Chiara Olla
- Department
of Physics, University of Cagliari, I-09042 Monserrato, Italy
| | - Antonio Cappai
- Department
of Physics, University of Cagliari, I-09042 Monserrato, Italy
| | - Maria Francesca Casula
- Department
of Mechanical, Chemical and Materials Engineering, University of Cagliari, Via Marengo 2, IT 09123 Cagliari, Italy
| | - Claudio Melis
- Department
of Physics, University of Cagliari, I-09042 Monserrato, Italy
| | - Luigi Stagi
- Department
of Chemistry and Pharmacy, Laboratory of Materials Science and Nanotechnology, University of Sassari, Via Vienna 2, 07100 Sassari, Italy
| | - Aatto Laaksonen
- Department
of Chemical and Geological Sciences, University
of Cagliari, I-09042 Monserrato, Italy,Department
of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, SE-106 91 Stockholm, Sweden,State Key
Laboratory of Materials-Oriented and Chemical Engineering, Nanjing Tech University, Nanjing 210009, P. R. China,Centre
of Advanced Research in Bionanoconjugates and Biopolymers, PetruPoni Institute of Macromolecular Chemistry, Aleea Grigore Ghica-Voda 41A, 700487 Iasi, Romania,Division
of Energy Science, Energy Engineering, Luleå
University of Technology, Luleå 97187, Sweden,
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6
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Madonia A, Sciortino A, Martin-Sabi M, Cannas M, Ammar S, Messina F, Schaming D. Electron transfer between carbon dots and tetranuclear Dawson-derived sandwich polyanions. Phys Chem Chem Phys 2022; 24:17654-17664. [PMID: 35834214 DOI: 10.1039/d2cp00447j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Among the photocatalysts which could be used for converting solar energy, polyoxometalates are often regarded as ideal candidates because of their remarkable performances in photocatalytic water splitting and photodegradation of pollutants. Nonetheless, these polyanions are only capable of absorbing UV light, unless coupled to a visible-light photosensitizer. Carbon nanodots are especially promising for this purpose because of their strong visible-light absorption, photostability, non-toxicity, and very low production costs. In this work we demonstrate the possibility of coupling carbon dots to polyoxometalates with different structures, by a simple self-assembly approach based on electrostatic interactions in solution phase. Our studies highlight an extremely efficient interaction between the two compounds, resulting in ultrafast photoinduced electron or energy transfer from carbon dots to the coupled polyoxometalates, depending on the structure of the latter, as revealed by a detailed study based on ultrafast transient absorption spectroscopy. The evidence herein provided shows how nanohybrids based on polyoxometalates photosensitized by carbon dots could find their place in photocatalytic applications, thanks to their remarkable efficiency and huge versatility.
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Affiliation(s)
- Antonino Madonia
- Université de Paris, ITODYS, UMR 7086 CNRS, 15 rue Jean-Antoine de Baïf, 75013 Paris, France.
| | - Alice Sciortino
- Università degli Studi di Palermo, DiFC, via Archirafi 36, 90123 Palermo, Italy.
| | - Mercè Martin-Sabi
- Université de Paris, ITODYS, UMR 7086 CNRS, 15 rue Jean-Antoine de Baïf, 75013 Paris, France.
| | - Marco Cannas
- Università degli Studi di Palermo, DiFC, via Archirafi 36, 90123 Palermo, Italy.
| | - Souad Ammar
- Université de Paris, ITODYS, UMR 7086 CNRS, 15 rue Jean-Antoine de Baïf, 75013 Paris, France.
| | - Fabrizio Messina
- Università degli Studi di Palermo, DiFC, via Archirafi 36, 90123 Palermo, Italy. .,Università degli Studi di Palermo, CHAB-ATeN Center, Viale delle Scienze, Edificio 18, 90128 Palermo, Italy
| | - Delphine Schaming
- Université de Paris, ITODYS, UMR 7086 CNRS, 15 rue Jean-Antoine de Baïf, 75013 Paris, France.
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7
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Stergiou A, Tagmatarchis N. Interfacing Carbon Dots for Charge-Transfer Processes. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2021; 17:e2006005. [PMID: 33522118 DOI: 10.1002/smll.202006005] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/25/2020] [Revised: 12/09/2020] [Indexed: 06/12/2023]
Abstract
Carbon dots (CDs) are a booming material and the most recent incomer in the big family of carbon nanostructures. Specifically, CDs are nanosized fluorescent core-shell nanoparticles with tunable absorption and emission spectra, with high solubility in aqueous media and common organic solvents. Herein, the origins and the development of these unique nanoscale structures are discussed, key synthetic routes are briefly described, and the utilization of CDs in light-induced charge-transfer schemes is mainly focused upon. Beyond the impact of the CD's surface on the photoluminescence properties, functionalization, by covalent or supramolecular means, permits controllable incorporation of new functionalities with novel photophysical properties. Furthermore, the dual nature of CDs as electron donating or electron accepting species, unveiled upon interfacing them with organic chromophores, highlights their potentiality in managing diverse charge-transfer processes. Novel mechanisms, such as symmetry-breaking photoinduced charge-transfer can be activated upon covalent functionalization of CDs with organic dyes. Without a doubt, participation of CDs in energy conversion schemes opens up a wide avenue that may lead to the development of novel prototype devices suitable for technological applications and related to photonics and optoelectronics.
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Affiliation(s)
- Anastasios Stergiou
- Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation, 48 Vassileos Constantinou Avenue, Athens, 11635, Greece
| | - Nikos Tagmatarchis
- Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation, 48 Vassileos Constantinou Avenue, Athens, 11635, Greece
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8
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Macairan JR, de Medeiros TV, Gazzetto M, Yarur Villanueva F, Cannizzo A, Naccache R. Elucidating the mechanism of dual-fluorescence in carbon dots. J Colloid Interface Sci 2021; 606:67-76. [PMID: 34388574 DOI: 10.1016/j.jcis.2021.07.156] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2021] [Revised: 07/23/2021] [Accepted: 07/31/2021] [Indexed: 11/30/2022]
Abstract
Carbon dots have garnered significant attention owing to their versatile and highly tunable optical properties; however, the origins and the underlying mechanism remains a subject of debate especially for dual fluorescent systems. Here, we have prepared carbon dots from glutathione and formamide precursors via a one-pot solvothermal synthesis. Steady state and dynamic techniques indicate that these dual fluorescent dots possess distinct emissive carbon-core and a molecular states, which are responsible for the blue and red optical signatures, respectively. To further glean information into the fluorescence mechanism, electrochemical analysis was used to measure the bandgaps of the two fluorescent states, while femtosecond transient absorption spectroscopy evidenced the two-state model based on the observed heterogeneity and bimodal spectral distribution. Our findings provide novel and fundamental insights on the optical properties of dual fluorescent dots, which can translate to more effective and targeted application development particularly in bioimaging, multiplexed sensing and photocatalysis.
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Affiliation(s)
- Jun-Ray Macairan
- Department of Chemistry and Biochemistry and the Centre for NanoScience Research, Concordia University, Montreal, QC H4B 1R6, Canada; Quebec Centre for Advanced Materials, Concordia University, Montreal, QC H4B 1R6, Canada
| | - Tayline V de Medeiros
- Department of Chemistry and Biochemistry and the Centre for NanoScience Research, Concordia University, Montreal, QC H4B 1R6, Canada; Quebec Centre for Advanced Materials, Concordia University, Montreal, QC H4B 1R6, Canada
| | - Michela Gazzetto
- Institute of Applied Physics, University of Bern, Sidlerstrasse 5, CH-3012 Bern, Switzerland
| | - Francisco Yarur Villanueva
- Department of Chemistry and Biochemistry and the Centre for NanoScience Research, Concordia University, Montreal, QC H4B 1R6, Canada; Quebec Centre for Advanced Materials, Concordia University, Montreal, QC H4B 1R6, Canada
| | - Andrea Cannizzo
- Institute of Applied Physics, University of Bern, Sidlerstrasse 5, CH-3012 Bern, Switzerland.
| | - Rafik Naccache
- Department of Chemistry and Biochemistry and the Centre for NanoScience Research, Concordia University, Montreal, QC H4B 1R6, Canada; Quebec Centre for Advanced Materials, Concordia University, Montreal, QC H4B 1R6, Canada.
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9
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Montes C, Soriano ML, Villaseñor MJ, Ríos Á. Carbon-based nanodots as effective electrochemical sensing tools toward the simultaneous detection of bioactive compounds in complex matrices. J Electroanal Chem (Lausanne) 2020. [DOI: 10.1016/j.jelechem.2020.114573] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
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10
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Kohl FR, Grieco C, Kohler B. Ultrafast spectral hole burning reveals the distinct chromophores in eumelanin and their common photoresponse. Chem Sci 2019; 11:1248-1259. [PMID: 34123249 PMCID: PMC8148383 DOI: 10.1039/c9sc04527a] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Eumelanin, the brown-black pigment found in organisms from bacteria to humans, dissipates solar energy and prevents photochemical damage. While the structure of eumelanin is unclear, it is thought to consist of an extremely heterogeneous collection of chromophores that absorb from the UV to the infrared, additively producing its remarkably broad absorption spectrum. However, the chromophores responsible for absorption by eumelanin and their excited state decay pathways remain highly uncertain. Using femtosecond broadband transient absorption spectroscopy, we address the excited state behavior of chromophore subsets that make up a synthetic eumelanin, DOPA melanin, and probe the heterogeneity of its chromophores. Tuning the excitation light over more than an octave from the UV to the visible and probing with the broadest spectral window used to study any form of melanin to date enable the detection of spectral holes with a linewidth of 0.6 eV that track the excitation wavelength. Transient spectral hole burning is a manifestation of extreme chemical heterogeneity, yet exciting these diverse chromophores unexpectedly produces a common photoinduced absorption spectrum and similar kinetics. This common photoresponse is assigned to the ultrafast formation of immobile charge transfer excitons that decay locally and that are formed among graphene-like chromophores in less than 200 fs. Raman spectroscopy reveals that chromophore heterogeneity in DOPA melanin arises from different sized domains of sp2-hybridized carbon and nitrogen atoms. Furthermore, we identify for the first time striking parallels between the excited state dynamics of eumelanin and disordered carbon nanomaterials, suggesting that they share common structural attributes. Seeing the colors in black: ultrafast transient hole burning spectroscopy reveals the absorption properties of discrete chromophores and their interactions in the skin pigment eumelanin.![]()
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Affiliation(s)
- Forrest R Kohl
- Department of Chemistry and Biochemistry, The Ohio State University 100 West 18th Avenue Columbus Ohio 43210 USA +1-614-688-2635
| | - Christopher Grieco
- Department of Chemistry and Biochemistry, The Ohio State University 100 West 18th Avenue Columbus Ohio 43210 USA +1-614-688-2635
| | - Bern Kohler
- Department of Chemistry and Biochemistry, The Ohio State University 100 West 18th Avenue Columbus Ohio 43210 USA +1-614-688-2635
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