Unraveling the interplay between hydrogen bonding and rotational energy barrier to fine-tune the properties of triazine molecular glasses

Abstract

Mexylaminotriazine derivatives form molecular glasses with outstanding glass-forming ability (GFA), high resistance to crystallization (glass kinetic stability, GS), and a glass transition temperature (Tg) above room temperature that can be conveniently modulated by selection of the headgroup and ancillary groups. A common feature of all these compounds is their secondary amino linkers, suggesting that they play a critical role in their GFA and GS for reasons that remain unclear because they can simultaneously form hydrogen (H) bonds and lead to a high interconversion energy barrier between different rotamers. To investigate independently and better control the influence of H bonding capability and rotational energy barrier on Tg, GFA and GS, a library of twelve analogous molecules was synthesized with different combinations of NH, NMe and O linkers. Differential scanning calorimetry (DSC) revealed that these compounds form, with a single exception, kinetically stable glasses with Tg values spanning a very broad range from -25 to 94 °C. While variable temperature infrared spectroscopy combined to chemometrics reveals that, on average, around 60% of the NH groups are still H-bonded as high as 40 °C above Tg, critical cooling rates obtained by DSC clearly show that molecules without H-bond donating linkers also present an outstanding GFA, meaning that H bonding plays a dominant role in controlling Tg but is not required to prevent crystallization. It is a high interconversion energy barrier, provoking a distribution of rotamers, that most efficiently promotes both GFA and resistance to crystallization. These new insights pave the way to more efficient glass engineering by extending the possible range of accessible Tg, allowing in particular the preparation of homologous glass-formers with high GS at ambient temperature in either the viscous or vitreous state.

Photochemical and Electrochemical Triggered Bis(hydrazone) Switch

“…With the aim of applying an estimative approach to measure the hydrogenb ond strength, the rotational energy profile of the dihedralangle between the hydrazone moiety and the pyridine ring was calculated at the DFT/B3LYP/6-311 + G(d,p) level of theory as the relationship between both parameters was previously described (Figure 9). [57] As observedi nF igure 9, the dihedral angle rotational profile exhibits inflexion points at approximately 0, 100, 130, À100, and À1308.I nflexion at 08 corresponds to the globalm inima for both isomers where the conformationa llows the maximum possible NÀH···N interaction. Although IUPAC defines the rotational barriera st he energy barrierb etween two adjacent minimap oints, ar otation about C11ÀC12 from À1308 or 1308 to 08 must overcomealocal maximum at 908,i ncreasing the energy barriera nd, consequently,h as ar otational barrier that corresponds to the NÀH···N interaction equal to 11.29 and 11.03 kcal mol À1 for 1-E,Z and 1-Z,Z,r espectively.…”

“…With the aim of applying an estimative approach to measure the hydrogen bond strength, the rotational energy profile of the dihedral angle between the hydrazone moiety and the pyridine ring was calculated at the DFT/B3LYP/6–311+G(d,p) level of theory as the relationship between both parameters was previously described (Figure ) …”

Supramolecular elastomers: Switchable mechanical properties and tuning photohealing with changes in supramolecular interactions

“…This ∼10 cm −1 energy difference between the CO stretching of P1‐X and P2 is indicative of the formation of regular well‐ordered hydrogen bonding network in the P1‐X state . Two new signals centered at 3435 cm −1 and 3258 cm −1 in the P1‐X state correspond to vibration of free and hydrogen bonded NH of the sym ‐triazine, respectively . Analysis of the infrared absorption profile of the P1‐M state showed non‐ordered urethane and sym ‐triazine hydrogen bonding motifs as well as a significant contribution of free urethane fragments (1738 cm −1 CO vibration).…”

Electric-Field-Induced Nanoscale Surface Patterning in Mexylaminotriazine-Functionalized Molecular Glass Derivatives

“…The difference in behavior observed with respect to polymers could be due to the absence of chain entanglement, as well as the presence of hydrogen bonds between molecules, even at temperatures above Tg, that result in differences in diffusion rates under different environments. For example, it has been demonstrated that the degree of hydrogen bonding in mexylaminotriazine glasses decreases as a function of temperature, 37 while the chain entanglement of polymers is only weakly dependent on temperature.…”