Prolific Polymorph Generator ROY in Its Liquid and Glass: Two Conformational Populations Mirroring the...

Area of Science:

• Physical Chemistry
• Solid-State Chemistry
• Spectroscopy

Background:

• 5-Methyl-2-[(2-nitrophenyl)amino]-3-thiophenecarbonitrile (ROY) exhibits numerous crystal polymorphs, suggesting complex molecular behavior.
• Understanding molecular conformations is crucial for explaining solid-state properties and polymorphism.

Purpose of the Study:

• To investigate the conformational landscape of ROY in its liquid and glassy states using infrared spectroscopy.
• To correlate molecular conformations with the observed crystal polymorphism of ROY.

Main Methods:

• Infrared (IR) spectroscopy was employed to study ROY in liquid and glassy states.
• Analysis of spectral data allowed for the identification and quantification of different conformer populations.
• Computational methods were used to explore the torsional energy surface and conformational preferences.

Main Results:

• Two distinct conformer populations of ROY were identified, with an equilibrium characterized by ΔH = 2.4 kJ/mol and ΔS = 8.0 J/K/mol.
• These conformers correspond to the global and local minima on the torsional energy surface.
• The local minimum conformation, featuring a more coplanar arrangement and greater π-conjugation, is relevant to the 13 observed crystal polymorphs.

Conclusions:

• The conformational equilibrium of ROY in condensed phases directly influences its extensive polymorphism.
• The energy barrier between conformers in the gas phase supports rapid equilibration, consistent with experimental observations.
• This study provides insights into the molecular origins of ROY's prolific polymorphism.