Dimethyldihydropyrene (DHP) based organic photochromic materials: synthesis and application

Chatterjee, Sheelbhadra (2024) Dimethyldihydropyrene (DHP) based organic photochromic materials: synthesis and application. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Sheelbhadra Chatterjee (18RS057)) 18RS057.pdf - Submitted Version Restricted to Repository staff only Download (11MB)

Abstract

The objective of this thesis entitled “Dimethyldihydropyrene based Organic Photochromic Materials: Synthesis and Application” is to discuss the photo-modulation of various properties of several dihydropyrene (DHP) based photochromic systems. The detailed synthesis, characterization, and photoisomerization studies of the systems are included in the thesis. The introductory chapter 1 deals with the concept of conductance modulation with the photochromic materials. Several photochromic systems e.g., azobenzenes, dithienylethenes (DTE), spiropyrans and also DHP systems are discussed in detail. It offers a comprehensive review on the light driven modulation of conductance with photoswitchable materials. Chapter 2 describes the alteration of conductance in tetraphenylethene (TPE)-DHP conjugate through stacking and unstacking of the system under different light sources. The system aggregates in an appropriate solvent system. The aggregation behavior of the system can be controlled either by changing the solvent system or light. The closed isomer offers better conductance than the open isomer with a response ratio of 66. In chapter 3, a cooperative photochromic behavior has been explained in a DHP-DTE conjugate system. The ring opening isomerization of DHP is simultaneously observed with the ring closure of DTE units. Three individual isomeric states can be achieved depending upon the external stimuli applied on the system. The photochromic properties of the system have been explained with through theoretical investigations. Further a couple of logic operation has been performed with this DHP-DTE conjugate system considering the applied light as input and the emission from the system as output. Chapter 4 deals with a reversible generation of organic radical anion in a photochromic system having two DHP unit substituted at the axial positions of a naphthalenediimide (NDI) core. The system enables the reversible formation of radicals under UV light exposure. The reversibility of the radical formation has been observed under electron paramagnetic resonance (EPR) experiment. Exposure to UV light generates a radical anion with the unpaired electron centered over the NDI core. On the other hand, irradiation with visible light causes the diminishment of the radical. Notably, the radical formation is reversible upon irradiation with visible light, allowing for multiple cycles of radical formation and diminishment. The formation of the radical anion is associated with a noticeable change in emission intensity where the neutral species is less emissive compared to the radical anion form.

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