16 research outputs found
Caractérisation de matériaux moléculaires amorphes pour optimiser leur préparation et leurs applications
Les matĂ©riaux molĂ©culaires amorphes, aussi appelĂ©s verres molĂ©culaires, sont constituĂ©s de molĂ©cules organiques de petite taille capables de sâorganiser de façon dĂ©sordonnĂ©e. En plus de prĂ©senter certaines des propriĂ©tĂ©s analogues Ă celles des polymĂšres, ils offrent des avantages supplĂ©mentaires, puisquâils sont des espĂšces isomolĂ©culaires dont la synthĂšse, la purification et la mise en Ćuvre sont facilitĂ©es par leur viscositĂ© relativement faible. Toutefois, la prĂ©paration souvent exigeante de ces matĂ©riaux et leur durĂ©e de vie utile limitĂ©e par leur tendance Ă relaxer vers lâĂ©tat cristallin demeurent des obstacles Ă leur utilisation pour certaines applications, e.g. opto-Ă©lectronique, nanolithographie, pharmaceutique. Le dĂ©veloppement de stratĂ©gies visant Ă faciliter la prĂ©paration de la phase vitreuse et Ă©viter sa cristallisation est donc essentiel Ă la conception de matĂ©riaux molĂ©culaires amorphes fonctionnels. Lâobjectif principal de cette thĂšse est dâĂ©tablir des relations entre la structure molĂ©culaire des verres molĂ©culaires et leurs propriĂ©tĂ©s. Pour y arriver, diffĂ©rentes librairies de composĂ©s modĂšles, des dĂ©rivĂ©s analogues de triazine ayant dĂ©montrĂ© une excellente capacitĂ© Ă former une phase vitreuse, sont utilisĂ©es pour i) dĂ©terminer lâinfluence de la nature et de la position des groupements sur la triazine; ii) explorer lâinfluence des liaisons hydrogĂšne sur les propriĂ©tĂ©s des verres lorsque leur structure comporte des groupements fonctionnels reconnus pour faciliter la cristallisation et lorsque leurs conditions de prĂ©paration se rapprochent de celles employĂ©es en industrie et iii) exploiter la phase amorphe afin dâĂ©tudier la photosensibilitĂ© des azobenzĂšnes (azo) en vue dâoptimiser leur utilisation dans des applications. Tout dâabord, lâinfluence des diffĂ©rents groupes substituants sur la triazine (groupements de tĂȘte, auxiliaires et liants) sur la capacitĂ© des composĂ©s Ă former une phase vitreuse (GFA), sur sa stabilitĂ© cinĂ©tique (GS) et sur sa tempĂ©rature de transition vitreuse (Tg) est Ă©tudiĂ©e. Un systĂšme de classification des composĂ©s dĂ©veloppĂ© Ă partir de mesures de calorimĂ©trie diffĂ©rentielle Ă balayage (DSC) et des mesures de spectroscopie infrarouge (IR) Ă tempĂ©rature variable combinĂ©es Ă des analyses chimiomĂ©triques facilitent la rationalisation des rĂŽles jouĂ©s par chaque groupe. Lâimpact des liaisons hydrogĂšne (H), de la barriĂšre Ă©nergĂ©tique de rotation et de lâencombrement stĂ©rique des groupements est ainsi dĂ©terminĂ©, permettant de conclure que le groupe de tĂȘte est le plus influent et que la prĂ©sence de liaisons H nâest pas essentielle au GFA mais quâelle est importante pour obtenir une Tg Ă©levĂ©e. Ensuite, lâinfluence des liaisons H sur les propriĂ©tĂ©s des verres se rapprochant de ceux exploitĂ©s dans lâindustrie est explorĂ©e. Des mesures de spectroscopie IR Ă tempĂ©rature variable, de DSC et de rĂ©solution de structures cristallines ont permis de conclure que les liaisons H rĂ©ussissent Ă nuire Ă la cristallisation des composĂ©s et ce, mĂȘme sâils sont simultanĂ©ment fonctionnalisĂ©s avec des motifs qui favorisent la cristallisation (empilements Ï-Ï entre dĂ©rivĂ©s stilbĂšnes fluorĂ©s et non fluorĂ©s). De plus, trois composĂ©s analogues fonctionnalisĂ©s avec un groupement de tĂȘte possĂ©dant une capacitĂ© dĂ©croissante Ă Ă©tablir des liaisons H (donneur, accepteur, aucune) ont Ă©tĂ© dĂ©posĂ©s en phase vapeur (PVD), une technique employĂ©e entre autres dans lâindustrie opto-Ă©lectronique pour Ă©valuer leur capacitĂ© Ă former des verres ultrastables. Les films ainsi prĂ©parĂ©s prĂ©sentent tous des propriĂ©tĂ©s similaires Ă celles des verres ultrastables prĂ©cĂ©demment Ă©tudiĂ©s, telles quâune plus grande densitĂ© et anisotropie, et sont tous plus stables que ceux prĂ©parĂ©s par refroidissement Ă partir de lâĂ©tat liquide. Toutefois, le verre formĂ© du composĂ© avec un groupement de tĂȘte donneur de liaisons H est moins stable que les autres dâau moins un ordre de grandeur, suggĂ©rant que les liaisons H limitent le niveau de stabilitĂ© atteignable par PVD. Finalement, un verre Ă base de triazine fonctionnalisĂ© avec un groupement azo est employĂ© pour Ă©tudier dâun point de vue molĂ©culaire les perturbations provoquĂ©es par la photoisomĂ©risation de lâazo. GrĂące Ă une nouvelle mĂ©thode de spectroscopie IR, il est possible dâobserver un gradient dâenvironnement molĂ©culaire le long de la molĂ©cule lors de la photoisomĂ©risation, permettant de soutenir certaines hypothĂšses relatives au dĂ©placement macroscopique de la matiĂšre qui en rĂ©sulte. Les mĂ©langes de verres Ă base de triazine servent aussi de plateforme idĂ©ale pour dĂ©coupler lâinfluence de la Tg et du contenu en azo sur la photo-orientation de lâazo, mais aussi sur la cinĂ©tique dâĂ©criture et lâefficacitĂ© des rĂ©seaux de diffraction (SRG). Ce travail permet ainsi de dĂ©terminer une zone optimale de Tg pour lâinscription de SRG. Ces nouvelles connaissances mĂšneront Ă la conception plus rationnelle de nouveaux verres molĂ©culaires, pouvant sâĂ©tendre Ă dâautres matĂ©riaux amorphes.Amorphous molecular materials, also known as molecular glasses, are small organic molecules capable of being organized in a disordered manner. In addition to sharing some of the useful properties of polymers, they offer additional advantages because they are isomolecular species for which synthesis, purification and processing are facilitated by a relatively low viscosity. However, the usually demanding preparation conditions of these materials and their limited functional lifetime due to their tendency to relax to the crystalline state remain obstacles to their use for certain applications, e.g. opto-electronics, nanolithography, pharmaceuticals. The development of strategies to facilitate the preparation of the vitreous phase and avoid its crystallization is therefore essential for the design of functional amorphous molecular materials. The main objective of this thesis is to establish relationships between the molecular structure of molecular glasses and their properties. To achieve it, various libraries of model compounds, analogues of triazine derivatives that have demonstrated excellent glass-forming ability, are used to i) determine the influence of the nature and the position of the groups on the triazine; ii) explore the influence of hydrogen (H) bonds on the properties of glasses when their structure includes functional groups known to facilitate crystallization and when their preparation conditions are similar to those used in industry; and iii) exploit the amorphous phase in order to study the photoresponsiveness of azobenzenes (azo) in order to optimize their use in different applications. The influence of the various substituent groups on the triazine (headgroup, ancillary and linkers) on the glass-forming ability (GFA), the kinetic glass stability (GS) and the glass transition temperature (Tg) of the compounds is first studied. A classification system based on differential scanning calorimetry (DSC) and variable temperature infrared spectroscopy (IR) measurements combined to chemometrics analyses facilitate the rationalization of the roles played by each group. The impact of the H-bonds, the energy of the rotation barrier, and the steric hindrance of the groups is determined, leading to the conclusion that the headgroup is the most influential group and that the presence of H-bonds is not essential to the GFA, but important to obtain a high Tg.
The influence of the H-bonds on the properties of glasses approaching those exploited in industry is then explored. Variable temperature IR spectroscopy measurements, DSC studies, and single crystal structure resolution have led to the conclusion that H-bonds impede the crystallization of the compounds even though they are simultaneously functionalized with moieties that promote crystallization (Ï-Ï stacking between fluorinated and non-fluorinated stilbene groups). In addition, three similar compounds functionalized with a headgroup presenting a decreasing capability to establish H-bonds (donor, acceptor, none) were vapor-deposited (PVD), a technique used, among others, in the opto-electronic industry, to evaluate their capability to form ultrastable glasses. These PVD glasses all show properties that are similar to those previously reported for ultrastable glasses, including higher density and anisotropy, and are all more kinetically stable than glasses prepared by cooling from the viscous state. However, the PVD glasses prepared with a H-bond donor headgroup are less stable than the others by at least an order of magnitude, suggesting that H-bonds limit the level of kinetic stability achievable by PVD. Finally, a triazine molecular glass functionalized with an azo group is used to study, from a molecular point of view, the perturbations caused by the photoisomerization of the azo. A new IR spectroscopy method was developed to observe a molecular environment gradient along the molecule during photoisomerization, making it possible to support certain hypotheses concerning the resulting macroscopic transport of the material. Triazine-based molecular glass blends are also used as an ideal platform for decoupling the influence of Tg and azo content on the azo photo-orientation, but also on the inscription kinetics and the diffraction efficiency of surface relief gratings (SRGs). This work enables the determination of an optimal Tg range for the inscription of SRGs. Altogether, these new insights will lead to a more rational design of new molecular glasses, which can extend to other amorphous molecular materials
Photoactive/passive molecular glass blends : an efficient strategy to optimize azomaterials for surface relief grating inscription
: Irradiation of azomaterials causes various photophysical and photomechanical effects that can be exploited
for the preparation of functional materials such as surface relief gratings (SRGs). Herein, we develop and apply an efficient
strategy to optimize the SRG inscription process by decoupling, for the first time, the important effects of the azo content
and glass transition temperature (Tg). We prepare blends of a photoactive molecular glass functionalized with the azo Disâ
perse Red 1 (gDR1) with a series of analogous photopassive molecular glasses. Blends with 10 and 40 mol% of gDR1 are
completely miscible, present very similar optical properties, and cover a wide range of Tg from below to well above ambient
temperature. SRG inscription experiments show that the diffraction efficiency (DE), residual DE and initial inscription rate
reach a maximum when Tg is 25 to 40 °C above ambient temperature for low to high azo content, respectively. Indeed, for
a fixed 40 mol% azo content, choosing the optimal Tg enables doubling the SRG inscription rate and increasing DE sixfold.
Moreover, a higher azo content enables higher DE for a similar Tg. Spectroscopy measurements indicate that the photoâ
orientation of DR1 and its thermal stability are maximal with Tg around 70 °C, independent of the azo content. We conclude
that the SRG potential of azomaterials depends on their capability to photoâorient but that the matrix rigidity eventually
limits the inscription kinetics, leading to an optimal Tg that depends on the azo content. This study exposes clear material
design guidelines to optimize the SRG inscription process and the photoactivity of azomaterials
Roadmap on energy harvesting materials
Ambient energy harvesting has great potential to contribute to sustainable development and address growing environmental challenges. Converting waste energy from energy-intensive processes and systems (e.g. combustion engines and furnaces) is crucial to reducing their environmental impact and achieving net-zero emissions. Compact energy harvesters will also be key to powering the exponentially growing smart devices ecosystem that is part of the Internet of Things, thus enabling futuristic applications that can improve our quality of life (e.g. smart homes, smart cities, smart manufacturing, and smart healthcare). To achieve these goals, innovative materials are needed to efficiently convert ambient energy into electricity through various physical mechanisms, such as the photovoltaic effect, thermoelectricity, piezoelectricity, triboelectricity, and radiofrequency wireless power transfer. By bringing together the perspectives of experts in various types of energy harvesting materials, this Roadmap provides extensive insights into recent advances and present challenges in the field. Additionally, the Roadmap analyses the key performance metrics of these technologies in relation to their ultimate energy conversion limits. Building on these insights, the Roadmap outlines promising directions for future research to fully harness the potential of energy harvesting materials for green energy anytime, anywhere
Metalâligand interactions and salt bridges as sacrificial bonds in mussel byssus-derived materials
The byssus that anchors mussels to solid surfaces is a protein-based material combining strength and toughness as well as a self-healing ability. These exceptional mechanical properties are explained in part by the presence of metal ions forming sacrificial bonds with amino acids. In this study, we show that the properties of hydrogel films prepared from a byssus protein hydrolyzate (BPH) can also be improved following the biomimetic formation of sacrificial bonds. Strengthening and toughening of the materials are both observed when treating films with multivalent ions (Ca2+ or Fe3+) or at the BPH isoelectric point (pI) as a result of the formation of metalâligand bonds and salt bridges, respectively. These treatments also provide a self-healing behavior to the films during recovery time following a deformation. While pI and Ca2+ treatments have a similar but limited pH-dependent effect, the modulus, strength, and toughness of the films increase largely with Fe3+ concentration and reach much higher values. The affinity of Fe3+ with multiple amino acid ligands, as shown by vibrational spectroscopy, and the more covalent nature of this interaction can explain these observations. Thus, a judicious choice of treatments on polyampholyte protein-based materials enables control of their mechanical performance and self-healing behavior through the strategic exploitation of reversible sacrificial bonds
Triazineâbased molecular glasses frustrate the crystallization of barbiturates
Hydrogen bonding is a key element of supramolecular chemistry and is often used in crystal engineering to direct crystal packing. In particular, systems where motifs with multiple hydrogen (H) bonds are present, such as the donorâacceptorâdonor â acceptorâdonorâacceptor (DADâADA) synthon, can be used to generate various supramolecular architectures. However, H-bonding can also be used to frustrate crystallization if it impedes an efficient molecular packing, instead resulting in glass formation. Herein, triazine-based molecular glass-formers, which can form multiple hydrogen bonds and show outstanding resistance to crystallization, are strategically used to hinder the crystallization of barbiturate derivatives, even in blends with low molar fractions, depending on the structure of the glass-former. Besides the strong DADâADA motifs, the molecules can form several sub-optimal motifs that can serve to hinder the crystallization of the barbiturate component during solvent evaporation or cooling. A triazine derivative with a covalently bound barbituric acid moiety was also synthesized, and did also not show any crystallization, showing that the presence of strong and predictable hydrogen bonding motifs does not necessarily contribute to crystallization. Our results highlight molecular design guidelines to hinder the crystallization of a compound, either by covalent functionalization or by blending with a glass-former capable of establishing similar interactions, thus leading to a variety of motifs for glass engineering
Harnessing Direct(Hetero)Arylation in Pursuit of a Saddle-Shaped Perylene Diimide Tetramer
This contribution explores the direct(hetero)
arylation (DHA) cross-coupling of a saddle-like, Ï-conjugated cyclooctatetrathiophene
(Th4) core with the N-annulated perylene diimide (PDI)
chromophore. Replacing the bulky pivalic acid with acetic acid enabled a facile
cross-coupling, selectively forming a PDI tetramer (Th4PDI4) in a 70% overall yield. The optoelectronic
properties of Th4PDI4 were characterized and density functional theory (DFT)
was used to calculate the optimized molecular geometry and molecular orbitals
(MOs). MOs determined by cyclic voltammetry corresponded well with those calculated
using DFT. The molecular geometry calculated by DFT showed Th4PDI4 adopts two separate PDI-PDI conformations (propeller
and double-decker). Organic photovoltaic (OPV) devices were fabricated using a
blend of PTB7-Th:Th4PDI4, where an initial power conversion efficiency (PCE)
of 1.89 % was improved by testing a series of solvent additives and thermal
annealing techniques. Through use of 3 % (v/v) 1-chloronaphthalene additive, a
combination of higher short circuit current (Jsc = 10.2 mA/cm2)
and fill factor (FF = 42 %) led to an overall increase in PCE to 4.26 %. </p
Direct (Hetero)Arylation for the Synthesis of Molecular Materials: Coupling Thieno[3,4-c]pyrrole-4,6-dione with Perylene Diimide to Yield Novel Non-Fullerene Acceptors for Organic Solar Cells
Herein we report on the synthesis of an N-annulated perylene diimide (PDI) disubstituted thieno[3,4-c]pyrrole-4,6-dione (TPD) molecular acceptor (PDIâTPDâPDI) by direct heteroarylation (DHA) methods. Three sets of DHA conditions that explore the effects of solvent, temperature, and catalyst were employed to find the optimal conditions for the synthesis of two PDIâTPDâPDI derivatives. We then selected one PDIâTPDâPDI for use as a non-fullerene acceptor in organic solar cell devices with the donor polymer PBDB-T. Active layer bulk-heterojunction blends were modified using several post-deposition treatments, including thermal annealing, solvent vapour annealing, and high boiling solvent additives. It was found that active layers cast from o-dichlorobenzene with a 3% v/v diphenylether additive yielded films with adequate phase separation, and subsequently gave the best organic solar cell performance, with power conversion efficiencies greater than 3%
Glass versus crystal : a balancing act between competing intermolecular interactions
Hydrogen (H) bonds can be used either for crystal engineering or for designing compounds capable of forming very stable glassy phases. Herein, a second type of directional noncovalent interaction, ÏâÏ stacking, is introduced to establish the interplay between both types of interactions on crystal and glass formation. For this purpose, two mexylaminotriazine derivatives incorporating 2,3,4,5,6-pentafluorostilbene groups (with or without a H-bond donor at the 2 position of the triazine) and their nonfluorinated analogues were synthesized to compare their glass-forming and crystallization properties. Although all four compounds showed glass-forming ability, only the fluorinated compounds showed crystallization with kinetics strongly affected by the presence or absence of the H-bond donor group. X-ray diffraction of the pentafluorostilbene-containing derivatives revealed an extended ÏâÏ stacking interaction different from that of 2,3,4,5,6-pentafluorostilbene. These results, combined with infrared spectroscopy measurements, suggest that ÏâÏ stacking promotes crystallization whereas hydrogen bonding impedes it due to the higher conformational constraints imposed by ÏâÏ stacking, thereby decreasing the degrees of liberty and the possibilities for secondary interactions with other molecules
Influence of Hydrogen Bonding on the Kinetic Stability of Vapor Deposited Glasses of Triazine Derivatives
The effect of hydrogen bonding on the properties of vapor deposited glasses is studied.It has recently been established that physical
vapor deposition (PVD) can produce organic glasses with
enhanced kinetic stability, high density, and anisotropic
packing, with the substrate temperature during deposition
(Tsubstrate) as the key control parameter. The influence of
hydrogen bonding on the formation of PVD glasses has not
been fully explored. Herein, we use a high-throughput
preparation method to vapor-deposit three triazine derivatives
over a wide range of Tsubstrate, from 0.69 to 1.08Tg, where Tg is
the glass transition temperature. These model systems are
structural analogues containing a functional group with
different H-bonding capability at the 2-position of a triazine
ring: (1) 2-methylamino-4,6-bis(3,5-dimethyl-phenylamino)-
1,3,5-triazine (NHMe) (H-bond donor), (2) 2-methoxy-4,6-bis(3,5-dimethyl-phenylamino)-1,3,5-triazine (OMe) (H-bond
acceptor), and (3) 2-ethyl-4,6-bis(3,5-dimethyl-phenylamino)-1,3,5-triazine (Et) (none). Using spectroscopic ellipsometry, we
find that the Et and OMe compounds form PVD glasses with relatively high kinetic stability, with the transformation time (scaled
by the α-relaxation time) on the order of 103
, comparable to other highly stable glasses formed by PVD. In contrast, PVD glasses
of NHMe are only slightly more stable than the corresponding liquid-cooled glass. Using IR spectroscopy, we find that both the
supercooled liquid and the PVD glasses of the NHMe derivative show a higher average number of bonded NH per molecule than
that in the other two compounds. These results suggest that H-bonds hinder the formation of stable glasses, perhaps by limiting
the surface mobility. Interestingly, despite this difference in kinetic stability, all three compounds show properties typically
observed in highly stable glasses prepared by PVD, including a higher density and anisotropic molecular packing (as characterized
by IR and wide-angle X-ray scattering)1) U.S. Department of Energy,
Office of Science, Basic Energy Sciences, under Award (DESC000216)
2) Natural Sciences and Engineering
Research Council of Canada (NSERC)
3) University of Wisconsinâ
Madison MRSEC (DMR-1121288
Submolecular Plasticization Induced by Photons in Azobenzene Materials
We demonstrate experimentally for
the first time that the illumination
of azobenzene derivatives leads to changes in molecular environment
similar to those observed on heating but that are highly heterogeneous
at the submolecular scale. This localized photoplasticization, which
can be associated with a free volume gradient, helps to understand
the puzzling phenomenon of photoinduced macroscopic material flow
and photoexpansion upon illumination far below the glass transition
temperature (<i>T</i><sub>g</sub>). The findings stem from
the correlation of infrared (IR) spectral band shifts measured upon
illumination with those measured at controlled temperatures for two
amorphous DR1-functionalized azo derivatives, a polymer, pDR1A, and
a molecular glass, gDR1. This new approach reveals that IR spectroscopy
can be used as an efficient label-free molecular-scale thermometer
that allows the assignment of an effective temperature (<i>T</i><sub>eff</sub>) to each moiety in these compounds when irradiated.
While no band shift is observed upon illumination for the vibrational
modes assigned to backbone moieties of pDR1A and gDR1 and a small
band shift is found for the spacer moiety, dramatic band shifts are
recorded for the azo moiety, corresponding to an increase in <i>T</i><sub>eff</sub> of up to nearly 200 °C and a molecular
environment that is equivalent to thermal heating well above the bulk <i>T</i><sub>g</sub> of the material. An irradiated azo-containing
material thus combines characteristic properties of amorphous materials
both below and above its bulk <i>T</i><sub>g</sub>. The
direct measurement of <i>T</i><sub>eff</sub> is a powerful
probe of the local environment at the submolecular scale, paving the
way toward better rationalization of photoexpansion and the athermal
malleability of azo-containing materials upon illumination below their <i>T</i><sub>g</sub>