Crystal Engineering of Soft Organic Molecular Materials: Mechanical and Optical Properties

Ahmad, Shamim (2025) Crystal Engineering of Soft Organic Molecular Materials: Mechanical and Optical Properties. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Shamim Ahmad (19RS024)) 19RS024.pdf - Submitted Version Restricted to Repository staff only Download (13MB)

Abstract

The study of organic functional crystals has been greatly enhanced by crystal engineering. Molecular materials that are deformable both irreversibly and reversibly have been investigated. With the potential to increase the practical applicability of self-sustainable molecular materials, the discovery of self-healing molecular crystals that actuate on a time scale of milliseconds has attracted a lot of attention lately. It is known that globular molecules can exhibit a reorientationally disordered phase. They are referred to as plastic crystals (PCs) because they preserve long-range lattice order. PCs have been investigated because of their intriguing phase transitions and other benefits (such as changes in crystallographic symmetry, molecular translation, and morphological tunability). There is a gap in the structure-property correlations since PCs have not been thoroughly examined from the perspective of crystal engineering, despite tremendous progress. The foundations of organic self-healing crystals and polymorphic phase transitions in plastic crystals are examined from a mechanical and optical standpoint in my dissertation study. The concepts about current discoveries in soft materials, various instrumentation approaches, and our strategy for overcoming the difficulties are covered in the introductory chapter, Chapter 1. A novel PC (adamantly derivative) with a high entropy of transition is described in Chapter 2. Furthermore, temperature-resolved Mueller matrix measurements and its switching of Second Harmonic Generation (SHG) have been investigated. An organic plastic crystal with ultralow hysteretic phase transition is described in Chapter 3, and a temperature-dependent nanoindentation investigation demonstrates how the mechanical property parameters drastically change during the phase transition. The incorporation of a phase transition in a solid through the covalent bonding of a globular molecule is demonstrated in Chapter 4. In addition to the crystals' elastic mechanical flexibility, they also exhibit thermosalient/thermobending activity. The impact of various halogen atom substitutions on the crystal packing, mechanical characteristics, and self-healing behavior is illustrated in Chapter 5 in a millisecond timescale.

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