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Polymorphism-driven Distinct Nanomechanical, Optical, Photophysical, and Conducting Properties in a
K S Bejoymohandas1,2, Ashish Redhu3, Chithra H Sharma4
1Chemical Science and Technology Division, CSIR-National Institute for Interdisciplinary Science and Technology Thiruvananthapuram, Kerala, 695019, India.
Chemistry (Weinheim an Der Bergstrasse, Germany)
|December 1, 2023
Summary
Polymorphism in organic conjugated molecules significantly impacts properties. Ethyl-2-(1-benzothiophene-2-yl)quinoline-4-carboxylate (BZQ) dimorphs show distinct semiconductor and insulator behaviors, mechanical properties, and photoluminescence, highlighting polymorphism
Area of Science:
- Materials Science
- Solid-State Chemistry
- Organic Electronics
Background:
- Polymorphism in organic conjugated small molecules offers insights into microstructure-property relationships.
- Ethyl-2-(1-benzothiophene-2-yl)quinoline-4-carboxylate (BZQ) exists as two distinct crystal forms: block-like (BZB) and needle-like (BZN).
- These polymorphs exhibit varied molecular packing and intermolecular interactions.
Purpose of the Study:
- To investigate how distinct crystal structures of BZQ dimorphs influence their electronic, mechanical, and photophysical properties.
- To explore the relationship between molecular arrangement, conductivity, and light emission in organic crystal polymorphs.
Main Methods:
- Crystallography to determine molecular packing in BZB and BZN forms.
- Electrical conductivity measurements to assess semiconductor/insulator behavior.
- Nanomechanical testing (nanoindentation) to evaluate mechanical properties.
- Photoluminescence spectroscopy and waveguiding experiments to study optical properties.
Main Results:
- BZB crystals with slip-stacked columns exhibit semiconductor properties, while BZN with zig-zag packing acts as an insulator.
- BZB crystals are significantly softer than BZN crystals due to differences in strain relaxation mechanisms.
- BZN crystals demonstrate passive waveguiding, and both dimorphs are blue-emissive, with BZN showing higher quantum yield.
- The study identified light-emitting crystal polymorphs with varying electrical conductivity, a rare phenomenon.
Conclusions:
- Polymorphism plays a crucial role in modulating the functional properties of organic molecular materials.
- Distinct crystal packing directly correlates with observable electronic, mechanical, and photophysical characteristics.
- The findings highlight the potential of exploring polymorphism for designing advanced functional materials with tunable properties.
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