Stimuli-Responsive Organic Molecules for Tunable Control of Material Properties

Molla, Sariful (2026) Stimuli-Responsive Organic Molecules for Tunable Control of Material Properties. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Sariful Molla (20RS119)) 20RS119.pdf - Submitted Version Restricted to Repository staff only Download (18MB)

Abstract

This thesis aims to investigate the light- and heat-mediated control of molecular properties in novel photoswitchable dimethyldihydropyrene-based systems. The work involved the synthesis, characterization, and detailed studies of both ring-closed and ring-opened dimethldihydropyrenes. In recent times, controlling molecular properties with an external stimulus has been at the centre of focus. With controllable molecular properties, we can precisely control where and when the reaction or molecular functions occur. In this regard, a bistate molecular switch can generate two different responses, either “ON” or “OFF” state, and has been widely explored for numerous applications. Starting from photoswitchable drug delivery agents, smart medicines, and diagnostics in biomedical applications, to smart screens, switchable transistors, and molecular energy storage systems (MOST) in materials chemistry, the potential applications of these materials are limitless and can be found in every possible field. The introductory chapter, Chapter 1, covers the principles of switching of dimethyldihydropyrene and how the multiple stimuli work together to generate more than two species in photochromic systems. We will briefly discuss how these multi-state systems can be used to regulate more complex systems, such as protein folding or multi-responsive molecular logics for quantum computing. In Chapter 2, we examined the design principles and challenges involved in developing multistate systems. We have shown how DHP and Azobenzene, despite having overlapped absorption spectra, can be coupled to generate a multi-responsive system. Chapter 3 demonstrates that a light-driven modulation of aromaticity activates a chargetransfer emissive state accessible under visible excitation, whereas alternative irradiation conditions produce a persistent organic radical cation. This dual optical and chemical functionality establishes a versatile strategy for on-demand imaging and reactive applications using one molecular scaffold. The practical application of DHP derivatives has been limited due to a lack of knowledge about solid-state switching behaviour. In Chapter 4, we address this challenge by investigating how solid-state switching can be preserved in polymer-blended thin films. Next, the light-driven structural change of DHP substantially changes the π- conjugation and hence modifies the energy gap, also, a significant amount of morphology change is expected. In my last working chapter, Chapter 5, we discussed the dynamic control of charge Transportation using the DHP π-switch.

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