Optical spectroscopy; Photo electrochemistry; Complex impedance spectroscopy

Keywords: Luminescence, time resolved, luminance, excitation / emission mapping, colorimetry, thermochromism, electrochemical impedance spectroscopy, energy level determination, photoelectrochemistry, charge carrier transfer

The CSM team has gradually developed complementary and high-quality technical platforms in the field of optical and electronic characterizations: the Caphter platform (https://scanmat.univ-rennes1.fr/la-plate-forme-caphter) attached to the UMS ScanMAT, the "Luminescence and Colorimetry" technical platform attached by convention to the NanoRennes platform . These platforms are intended to be accessible to all academic partners (fundamental research) or from the socio-economic world (services, research contracts). They bring together high-performance equipment used and maintained by highly qualified personnel (BIATS, IT, C or EC) which allow our team to deploy its research activity along a continuum ranging from fundamental research to the study of technologically interesting materials.

The Luminescence and Colorimetry technical platform has been designed, with the financial support of Rennes Métropole (AES, AIS), to study the photophysical properties of rare earth-based coordination polymers likely to find their application as sensors (chemical or thermometric) or taggants (anti counterfeiting). In addition to classical UV vis and IR absorption spectrometers, it has the necessary equipment (spectrofluorometers) to study their luminescence properties (lifetime from the second to the nanosecond scale, quantum yields (290   850 nm), emission and excitation spectra, 3D scan (emission vs. excitation), CIE coordinates (x, y). ...) in wide excitation (250   850 nm), emission (280 – 1700 nm) and temperature (77 K – 383 K) wavelength ranges thanks to a cryostat and a Peltier effect module. An originality of this platform is its ability to measure the luminescence intensity (luminance in Cd.m 2) of compounds in powder form. Although essential for the study of the efficiency of materials, this measurement is currently very little practiced and, to our knowledge, our team is the only one to practice it on coordination compounds. In the framework of the next contract, our team is pursuing two main objectives (i) the acquisition of a cryogen free type cryostat allowing luminescence measurements down to 4 K (request made within the framework of the CPER). This would allow measuring the position of the Stark sublevels whose knowledge is fundamental for the elaboration of magneto-optical correlations in rare earth-based coordination compounds. This type of cryostat, which does not use helium, addresses ecological and financial concerns; (ii) to produce a prototype that would allow the transition from relative luminance measurements to absolute measurements. This prototype is currently under development.

Thus, this platform will allow us, during the next five year contract, to continue the study of the photophysical mechanisms (inter-system crossing, intermetallic energy transfer, sensitization efficiency, back transfer,...) that govern the luminescence properties of rare earth-based coordination compounds. This equipment is crucial for the joint laboratory ChemInTag. The measurements carried out on this platform will also allow us a better understanding of the dynamic magnetic properties of these systems. It will also be used to study other types of compounds such as mixed anion materials (oxynitrides, oxysulfides, oxycyanamides) studied in the framework of an inter-team project (CSMV&C), CuI-based supramolecular compounds (ANR PRC Project 'SMAC' and PICS Project with Germany) or 4f 3d coordination compounds (ECOS Project with Chile).

Figure :  Colorimetric coordinates and pictures of pellets of single-crystals, microcrystalline powders and colloidal suspension of TbEu-based coordination polymers (left). Emission spectrum in the visible and IR regions of a molecular alloys containing NdIII, SmIII, Eu III, Gd III, Tb III and Dy III ions as luminescent bar-code (top right). Solid-state emission spectra and emission decay lifetime measured with variable temperature (80-300K) on a Cu(I)-based molecule.

Recent works illustrating the Luminescence and colorimetry technical platform

(1) Abdallah, A.; Puget, M.; Daiguebonne, C.; Suffren, Y.; Calvez, G.; Bernot, K.; Guillou, O., A new series of lanthanide-based complexes with a bis(hydroxy)benzoxaborolone ligand synthesis, crystal structure, and magnetic and optical properties. Crystengcomm 2020, 22, 2020-2030.
(2) Pointel, Y.; Houard, F.; Suffren, Y.; Daiguebonne, C.; Le Natur, F.; Freslon, S.; Calvez, G.; Bernot, K.; Guillou, O., High Luminance of Heterolanthanide-Based Molecular Alloys by Phase-Induction Strategy. Inorg. Chem. 2020, 59, 11028-11040.
(3) Pointel, Y.; Suffren, Y.; Daiguebonne, C.; Le Natur, F.; Freslon, S.; Calvez, G.; Bernot, K.; Guillou, O., Rational Design of Dual IR and Visible Highly Luminescent Light-Lanthanides-Based Coordination Polymers. Inorg. Chem. 2020, 59, 10673-10687.
(4) Evrard, Q.; Houard, F.; Daiguebonne, C.; Calvez, G.; Suffren, Y.; Guillou, O.; Mannini, M.; Bernot, K., Sonocrystallization as an Efficient Way to Control the Size, Morphology, and Purity of Coordination Compound Microcrystallites Application to a Single-Chain Magnet. Inorg. Chem. 2020, 59, 9215-9226.
(5) Houard, F.; Evrard, Q.; Calvez, G.; Suffren, Y.; Daiguebonne, C.; Guillou, O.; Gendron, F.; Le Guennic, B.; Guizouarn, T.; Dorcet, V.; Mannini, M.; Bernot, K., Chiral Supramolecular Nanotubes of Single-Chain Magnets. Angew. Chem. Int. Ed. 2020, 59, 780-784.
(6) Evariste, S.; Khalil, A. M.; Kerneis, S.; Xu, C.; Calvez, G.; Costuas, K.; Lescop, C., Luminescent vapochromic single crystal to single crystal transition in one-dimensional coordination polymer featuring the first Cu(i) dimer bridged by an aqua ligand. Inorg. Chem. Front. 2020, 7, 3402-3411.
(7) Evariste, S.; Moussa, M. E. S.; Wong, H.-L.; Calvez, G.; Yam, V. W.-W.; Lescop, C., Straightforward Preparation of a Solid-state Luminescent Cu-11 Polymetallic Assembly via Adaptive Coordination-driven Supramolecular Chemistry. Z. Anorg. Allg. Chem. 2020, 646, 754-760.
(8) Moussa, M. E. S.; Khalil, A. M.; Evariste, S.; Wong, H.-L.; Delmas, V.; Le Guennic, B.; Calvez, G.; Costuas, K.; Yam, V. W.-W.; Lescop, C., Intramolecular rearrangements guided by adaptive coordination-driven reactions toward highly luminescent polynuclear Cu(I) assemblies. Inorg. Chem. Front. 2020, 7, 1334-1344.
(9) Maouche, R.; Belaid, S.; Benmerad, B.; Bouacida, S.; Freslon, S.; Daiguebonne, C.; Suffren, Y.; Calvez, G.; Bernot, K.; Roiland, C.; Le Polles, L.; Guillou, O., Luminescence properties of lanthanide complexes-based molecular alloys. Inorg. Chim. Acta 2020, 501.
(10) de Rohello, E. L.; Suffren, Y.; Merdrignac-Conanec, O.; Guillou, O.; Chevire, F., Effect of cationic substitutions on the photoluminescence properties of Eu2+ doped SrCN2 prepared by a facile C3N4 based synthetic approach. J. Eur. Ceram. Soc. 2020, 40, 6316-6321.

Optical characterizations (Luminescence and Colorimetry technical plateform)

1 spectroflurimeter Fluorolog-3 HJY (CW and pulsed Xe lamp, R928 PMT and InGaAs photodiode detectors, 250 1700 nm).
1 spectroflurimeter Fluoromax-4 Plus HJY (CW Xe lamp, R928 PMT detector, 250 850 nm).
1 TCSPC module coupled to 8 UV or VISIBLE sources HJY (280, 300, 320, 340, 360, 375, 395 and 405 nm) for lifetime measurement (500 ps - s).
2 integrating spheres HJY and GMP (330 850 nm and 250-2500 nm) for quantum yield measurements.
2 external visible IR sources (360 2600 nm and 450 5500 nm) Thorlabs.
1 cryostat OptistatCF Oxford Inst. + Peltier module HJY for measurements between 77 and 383 K.
2 spectroflurimeters LS55 et LS50B Perkin Elmer.
2 luminancemeters Majantys and ScienTec (Luminance prototype).
2 powermeter S120VC and S401C with PM100 and PM100D controller Thorlabs.
1 monochromator (190 560) Edmund Optics (Luminance prototype).
1 radiometer with 3 sensors (256, 312 and 365 nm) Fisher Sci.
1 calibrating lamp (230 1100 nm) Oceaninside.
4 leds 308 nm and 4 leds 325 nm Roithner (Luminance prototype).
1 spectrophotometer UV Visible Lambda 650 (Tungsten Halogen and Deuterium lamps, PMT R955 detector, 190 900 nm) + integrating sphere Perkin Elmer.
1 spectrofluorimeter FTIR with UATR + integrating sphere Perkin Elmer + IR-TGDSC Coupling line transfer.
1 spectroflurimeter for colorimetry (x and y coordinate determination).
1 IR Laser diode 980 nm Roithner.
Absorption cuvettes, émission cuvettes, quartz cells, capillaries, attenuating, cutoff and band pass filters, optical lens, small optical table, optical fibers…
1 optical oven Grosseron for optical consumables (absorption and emission cuvettes, capillaries,…)
1 Illuminating chamber Brant Ind.
1 inversed microscope Olympus with spectrometer Optoprim.

The Caphter platform is equipped with top of the art steady state and time resolved spectrometers. One of its many specificities relies on the sensitivity of its detectors in the vis-red-NIR area. Detection ranges from 250 up to 1700 nm. The pulsed femtosecond laser chain allows excitation from 280 up to 1080 nm and is used for two photon absorption induced emission, second harmonic emission generation, and TRPL studies. A pulsed picosecond laser diode reinforces the excitation possibilities. Hence, excited state lifetimes from few ps up to 300 µs (i.e. fluorescence and phosphorescence) can be recorded thanks to a streak camera working in the 250 – 950 nm range and a NIR-PMT detector which sensitivity ranges from 950 up to 1700 nm. The system is completed with a CCD spectrometer for steady state measurements. All experiments can be realized from 77K up to 450K. Recently, an atmosphere controller has equipped the sample chamber to work on tailored atmosphere (Ar + O2) with an O2 concentration ranging from few ppm up to 100%, of particular interest for singlet oxygen production studies with phosphorescent compounds.

Caphter hosts also a Duetta spectrometer able to perform absorption and steady state emission studies from 250 up to 1200 nm (colorimetry, excitation vs emission map, kinetic studies…) and, an absolute quantum yield measurements system that works on the 360-1100 nm range for solids, films and solutions.

Detailed description is provided following this link: Scanmat: les équipements de Caphter

These equipments are mandatory to study the emission properties of multiresponsive soft hybrid organic-inorganic materials like liquid crystals or polymers in working conditions.

Beside the caphter Platform, an optical polarized microscope equipped with an irradiation source, a linkam hotstage (80K – 600K) and a CCD spectrometer allows the studies of emissive thermotropic liquid crystals. All those equipments are used in the frame of local, national and international collaborations with our partners from Russia, Brazil, Germany and Spain.

Recent publications illustrating the use of these facilities

Emissive polymers

Khlifi, S.; Fournier Le Ray, N.; Paofai, S.; Amela-Cortes, M.; Akdas-Kilic, H.; Taupier, G.; Derien, S.; Cordier, S.; Achard, M.; Molard, Y., Self-erasable inkless imprinting using a dual emitting hybrid organic-inorganic material. Mater. Today 2020, 35, 34-41.
UR1-CNRS patent Eur. Pat. Appl. (2020), EP 3730588 A1 20201028, PCT Int. Appl.(2020), WO 2020216717 A1  20201029

Figure : Emission vs excitation maps of doped polymers containing a) a blue green organic emitter (Poxi ) and b) a blue green organic emitter  and a red NIR phosphorescent octahedral metal cluster (PHyb) in an air atmosphere, c) PHyb in a N2 atmosphere; d) a red NIR phosphorescent octahedral metal cluster (PMo) in an air atmosphere (intensity increases from dark blue to red); e) Emission spectra at 25°C observed under 405 nm excitation (laser diode 5mW) for Poxi (black), PHyb (irradiation time : 10 ms (blue), 10 s (red), PMo (green), inset: pictures of Poxi and PMo thin films under UV (365 nm) and sunlight; f) 1931 CIE coordinates diagram of Poxi (blue square) and PHyb in air atmosphere (red circle) or under N2 atmosphere (white triangles), PMo (green diamond), excitation varies from 360 up to 480 nm by 5 nm steps; Schematic presentation of writing (5 mW, 405 nm laser pointer) and imprinting process using UV-light  (exc = 365 nm, UV-2A 4w); photographs of PHyb under UV light (365 nm) and solar light; i) the erasing step is performed either by heating the sample up to 60°C during 5 minutes or by waiting at 20°C for an amount of time depending on the irradiation power used during the imprinting step.

They speak about it

Materials today News, April 2020
CNRS : la lettre innovation, March 2020
Les Echos, 5 May 2020
Le télégramme, 13 May 2020
L’Actualité Chimique, en bref, June 2020
Full sciences, n°2, Aug-Oct 2020, p 134

Ferreira Molina, E.; Martins de Jesus, N. A.; Paofai, S.; Hammer, P.; Amela-Cortes, M.; Robin, M.; Cordier, S.; Molard, Y., When a Red–NIR-Emissive Cs2[Mo6Br14] Interacts with an Active Diureasil–PEO Matrix: Design of Tunable and White-Light-Emitting Hybrid Material. Chem. Eur. J. 2019, 25 (67), 15248-15251.
Patent UR1-CNRS - U. Franca Eur. Pat. Appl., n: 17306490.8,30 / 10/2017; PCT Int. Appl. WO2019086477

Figure : CIE diagramme of hybrid diureasil samples. (TOC entry for Chem. Eur. J.)
Robin, M.; Dumait, N.; Amela-Cortes, M.; Roiland, C.; Harnois, M.; Jacques, E.; Folliot, H.; Molard, Y., Direct Integration of Red-NIR Emissive Ceramic-like AnM6Xi8Xa6 Metal Cluster Salts in Organic Copolymers Using Supramolecular Interactions. Chem. Eur. J. 2018, 24 (19), 4825-4829.

Figure : Supramolecular strategy of cluster compound integration in a polymer and red-NIR emitting diode realized with such hybrid.

Emissive liquid crystal

Khlifi, S.; Bigeon, J.; Amela-Cortes, M.; Dumait, N.; Loas, G.; Cordier, S.; Molard, Y., Switchable Two-Dimensional Waveguiding Abilities of Luminescent Hybrid Nanocomposites for Active Solar Concentrators. ACS Appl. Mater. Interfaces 2020, 12 (12), 14400-14407.

Figure : Scheme of PDLC cells designed for 2D waveguiding studies. (TOC entry for publication)

Bader, K.; Mueller, C.; Molard, Y.; Baro, A.; Ehni, P.; Knelles, J.; Laschat, S., Fluorenone imidazolium salts as novel de Vries materials. RSC Advances 2020, 10 (40), 23999-24016.
Knelles, J.; Beardsworth, S.; Bader, K.; Bruckner, J. R.; Bühlmeyer, A.; Forschner, R.; Schweizer, K.; Frey, W.; Giesselmann, F.; Molard, Y.; Laschat, S., Self-Assembly and Fluorescence of Tetracationic Liquid Crystalline Tetraphenylethene. ChemPhysChem 2019, 20 (17), 2210-2216.
Forschner, R.; Knelles, J.; Bader, K.; Müller, C.; Frey, W.; Köhn, A.; Molard, Y.; Giesselmann, F.; Laschat, S., Flavylium Salts: A Blooming Core for Bioinspired Ionic Liquid Crystals. Chem. Eur. J. 2019, 25 (56), 12966-12980.
Bader, K.; Baro, A.; Ehni, P.; Frey, W.; Guendemir, R.; Laschat, S.; Molard, Y., Novel Luminescent Diazafluorenone Liquid Crystals. Cryst. Growth Des. 2019, 19 (8), 4436-4452.
Guy, K.; Ehni, P.; Paofai, S.; Forschner, R.; Roiland, C.; Amela-Cortes, M.; Cordier, S.; Laschat, S.; Molard, Y., Lord of The Crowns: A New Precious in the Kingdom of Clustomesogens. Angew. Chem. Int. Ed. 2018, 57 (36), 11692-11696.
Gandubert, A.; Amela-Cortes, M.; Nayak, S. K.; Vicent, C.; Meriadec, C.; Artzner, F.; Cordier, S.; Molard, Y., Tailoring the self-assembling abilities of functional hybrid nanomaterials: from rod-like to disk-like clustomesogens based on a luminescent {Mo6Br8}4+ inorganic cluster core. J. Mater. Chem. C 2018, 6 (10), 2556-2564.
Ehni, P.; Guy, K.; Ebert, M.; Beardsworth, S.; Bader, K.; Forschner, R.; Buehlmeyer, A.; Dumait, N.; Roiland, C.; Molard, Y.; Laschat, S., Luminescent liquid crystalline hybrid materials by embedding octahedral molybdenum cluster anions with soft organic shells derived from tribenzo[18]crown-6. Dalton Trans. 2018, 47 (40), 14340 -14351.
Camerel, F.; Kinloch, F.; Jeannin, O.; Robin, M.; Nayak, S. K.; Jacques, E.; Brylev, K. A.; Naumov, N. G.; Molard, Y., Ionic columnar clustomesogens: associations between anionic hexanuclear rhenium clusters and liquid crystalline triphenylene tethered imidazoliums. Dalton Trans. 2018, 47 (32), 10884-10896.

Photocatalysis

Feliz, M.; Atienzar, P.; Amela-Cortes, M.; Dumait, N.; Lemoine, P.; Molard, Y.; Cordier, S., Supramolecular Anchoring of Octahedral Molybdenum Clusters onto Graphene and their Synergies in the Photocatalytic Water Reduction. Inorg. Chem. 2019, 58 (22), 15443-15454.

Figure : Interaction of metal cluster compound with graphene through electrostatic and pi-pi stacking forces.

Emissive nanoparticles for biological application

Brandhonneur, N.; Boucaud, Y.; Verger, A.; Dumait, N.; Molard, Y.; Cordier, S.; Dollo, G., Molybdenum cluster loaded PLGA nanoparticles as efficient tools against epithelial ovarian cancer. Int. J. Pharm. 2021, 592, 120079.
Dollo, G.; Boucaud, Y.; Amela-Cortes, M.; Molard, Y.; Cordier, S.; Brandhonneur, N., PLGA nanoparticles embedding molybdenum cluster salts: Influence of chemical composition on physico-chemical properties, encapsulation efficiencies, colloidal stabilities and in vitro release. Int. J. Pharm. 2020, 576, 119025.

Single layer of luminophores on Au substrate

M. Kepenekian, Y. Molard,K. Costuas,P. Lemoine,R. Gautier,S. Ababou-Girard,B. Fabre,P. Turban,S. Cordier, Red-NIR luminescence of self-assembled Mo6 inorganic cluster monolayer on Au(001), Mater. Horiz., 2019, 6, 1828-1833.

The photoelectrode characterization platform is an electrochemical characterization platform equipped with 3 potentiostats (2 PGSTAT 204 and 1 PGSTAT30, Methrohm), two of which are equipped with an impedance module (FRA32M, Metrohm, 10 µHz - 1 MHz), an autolab LED driver optical bench, a non-standardized optical fiber white light illuminator and soon an AM1.5 sun simulator. The room is equipped with air conditioning to perform measurements under standard conditions, at 25 ° C. 

All this set of equipment is dedicated to the study of charge transfer phenomena in the photoelectrodes through (photo)-electrochemical measurements (spectro-photo-electrochemistry or electrochemical impedance spectroscopy). The CSM team has the expertise to access i) the energy levels (gaps, nature of charge carriers, flat band potentials, charge carrier density) of the layers making up the photoelectrodes and ii) the kinetics of (photo)-induced charge transfers (time life, transport and recombination of charge carriers) between them. In the future, with the acquisition of the sun simulator obtain with the financial support of Rennes Métropole (AIS), these measurements could be carried out in standardized conditions under AM1.5. The determination of the photoconversion efficiency of solar energy of photovoltaic cells will be possible too. These characterizations are performed in order to realize band engineering and optimize photoelectrodes for photovoltaic and photocatalysis applications.

P. Bais, M T. Caldes, C. Guillot-Deudon, A. Renaud, M. Boujtita, S. Jobic and A. Lafond, Influence of the copper deficiency and anionic composition on band-energy diagram of bulk kesterite CZTSSe, Mater. Res. Bull., 2021, just accepted

Fig 1. Energy level and charge carrier density estimation of Cu2ZnSn(SxSe1-x)4 compounds (CZTSSe)  through the flat band potential measurements by Mott-Schottky method. S50 and A50 correspond to Cu2ZnSnS2Se2 and Cu-poor Cu1.70Zn1.15SnS2Se2 compounds, respectively.

Inorganic Molybdenum Clusters as light-harvester in all inorganic solar cells: a proof of concept, Chemistry Select, 2016, 1, 2284-2289. 

Fig 2. Determination of energy levels of clusters (c) by coupling electrochemical (a) cyclic voltammetry) and optical measurements (b) photoluminescence measurements).