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Engineering TADF, mechanochromism, and second harmonic up-conversion properties in regioisomeric substitution space
Abhijit Chatterjee1, Joy Chatterjee1, Subrahmanyam Sappati2
1Department of Chemistry, Indian Institute of Science Education and Research (IISER) Pune 411008 Maharashtra India p.hazra@iiserpune.ac.in.
Chemical Science
|December 11, 2023
Summary
This study reveals that the para-isomer, DPAPCN, shows superior thermally activated delayed fluorescence (TADF) efficiency due to optimal electronic properties. The ortho-isomer, DPAOCN, displays unique mechanochromic luminescence and nonlinear optical properties, unlike its meta and para counterparts.
Area of Science:
- Organic Chemistry
- Materials Science
- Photophysics
Background:
- Donor-acceptor molecules are crucial for optoelectronic applications.
- Regio-isomerism significantly influences molecular properties and solid-state behavior.
- Understanding structure-property relationships is key for designing advanced materials.
Purpose of the Study:
- To investigate the impact of regio-isomerism on TADF efficiency, crystal packing, and bulk properties.
- To compare the photophysical and nonlinear optical characteristics of ortho, meta, and para isomers.
- To explore potential applications in optoelectronics and sensing.
Main Methods:
- Synthesis of three donor-acceptor regio-isomers (DPAOCN, DPAMCN, DPAPCN).
- Photophysical characterization including TADF measurements in solution and solid-state.
- X-ray crystallography to analyze crystal packing and void volume.
- Mechanochromic luminescence and second harmonic generation (SHG) measurements.
Main Results:
- DPAPCN (para-isomer) demonstrated the highest TADF efficiency with a rapid RISC rate (∼10^6 s^-1) attributed to minimal ΔEST and maximal SOC.
- DPAOCN (ortho-isomer) exhibited reversible tri-color mechanochromic luminescence due to its non-centrosymmetric crystal structure and void volume.
- DPAPCN and DPAMCN (meta-isomer) were mechanically inert due to centrosymmetric packing.
- DPAOCN showed excellent SHG properties (χ(2) = 0.19 pm V^-1) and a high LIDT (13.27 GW cm^-2).
Conclusions:
- Regio-isomerism profoundly affects TADF efficiency, crystal packing, and resulting bulk properties.
- The ortho-isomer presents a promising platform for mechanochromic sensors and nonlinear optical devices.
- Strategic molecular design based on regio-isomerism can unlock diverse functionalities in organic materials.
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