Inter-enantiomer conversion dynamics and Johari–Goldstein relaxation of benzophenones

We employ temperature- and pressure-dependent dielectric spectroscopy, as well as differential scanning calorimetry, to characterize benzophenone and the singly-substituted ortho-bromobenzophenone derivative in the liquid and glass states, and analyze the results in terms of the molecular conformations reported for these molecules. Despite the significantly higher mass of the brominated derivative, its dynamic and calorimetric glass transition temperatures are only ten degrees higher than those of benzophenone. The kinetic fragility index of the halogenated molecule is lower than that of the parent compound, and is found to decrease with increasing pressure. By a detailed analysis of the dielectric loss spectra, we provide evidence for the existence of a Johari–Goldstein (JG) relaxation in both compounds, thus settling the controversy concerning the possible lack of a JG process in benzophenone and confirming the universality of this dielectric loss feature in molecular glass-formers. Both compounds also display an intramolecular relaxation, whose characteristic timescale appears to be correlated with that of the cooperative structural relaxation associated with the glass transition. The limited molecular flexibility of ortho-bromobenzophenone allows identifying the intramolecular relaxation as the inter-enantiomeric conversion between two isoenergetic conformers of opposite chirality, which only differ in the sign of the angle between the brominated aryl ring and the coplanar phenyl-ketone subunit. The observation by dielectric spectroscopy of a similar relaxation also in liquid benzophenone indicates that the inter-enantiomer conversion between the two isoenergetic helicoidal ground-state conformers of opposite chirality occurs via a transition state characterized by a coplanar phenyl-ketone moiety.

Topographical transition of submicron pillar array of azo molecular glass induced by circularly polarized light

The well-aligned submicron patterns on surfaces have attracted wide attention from scientific curiosity to practical applications. Understanding their formation and transition is highly desirable for efficient manufacture of the patterns for many usages. Here, we report a unique observation on self-organized topographical transition of submicron pillar array of an azo molecular glass, induced by irradiation with circularly polarized light. During gradual erasure of the patterns upon exposure to the light, which is a property of this material, a new set of pillars unexpectedly emerge with new one in middle of each triangle cell of the original array. The highly regular pillar array with triple area density is formed and finally stabilized in the process, as revealed by thorough investigation reported here. This unusual observation and its rationalization will be of benefit for deep understanding of the light–matter interaction and can be expected to be applied in different areas.

Negative-tone molecular glass photoresist for high-resolution electron beam lithography

A low molecular weight organic compound containing bis-phenol A backbone (BPA-6OH) is reported as a negative-tone photoresist. This material has a high glass transition temperature and excellent thermal stability. A good contrast, well-resolved line pattern around 73.4 nm and sensitivity of 52 µC cm −2 can be received for negative-tone molecular glass photoresist upon exposure in electron beam lithography system. It indicates that the negative-tone molecular glass photoresist is one of the promising candidates for use in electron beam lithography.