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Evaluating Donor Effects in Isoindigo-Based Small Molecular Fluorophores
Sajith M Vijayan1, Nicholas Sparks1, Juganta K Roy2
1Department of Chemistry and Biochemistry, University of Mississippi, Oxford, Mississippi 38677, United States.
The Journal of Physical Chemistry. A
|December 11, 2020
Summary
New donor-acceptor-donor (D-A-D) organic fluorophores were synthesized and studied for fluorescence imaging (FI) and optoelectronic applications. These triphenylamine (TPA)-capped isoindigo dyes exhibit tunable near-infrared (NIR) properties due to intramolecular charge transfer (ICT).
Area of Science:
- Organic Chemistry
- Materials Science
- Photophysics
Background:
- Small molecular organic fluorophores are crucial for fluorescence imaging (FI) and optoelectronic devices.
- Donor-acceptor-donor (D-A-D) architectures are effective for tuning photophysical properties.
Purpose of the Study:
- To design and synthesize novel triphenylamine (TPA)-capped D-A-D fluorophores based on an isoindigo core.
- To investigate the effect of varying heterocyclic donor units (3,4-ethylenedioxythiophene (EDOT), furan (FURAN), thiophene (THIO), and 1-methyl-1H-pyrrole (MePyr)) on the fluorophores' properties.
- To explore the potential of these fluorophores for fluorescence imaging and optoelectronic applications.
Main Methods:
- Synthesis of four symmetrical D-A-D fluorophores: II-EDOT-TPA, II-FURAN-TPA, II-THIO-TPA, and II-MePyr-TPA.
- Comprehensive photophysical, electrochemical, and computational analyses (DFT, TD-DFT).
- Investigation of structural and electronic properties, including electron density distribution and frontier molecular orbitals.
Main Results:
- Successful synthesis of TPA-capped isoindigo fluorophores with varied heterocyclic donors.
- Experimental and theoretical data confirmed intramolecular charge transfer (ICT) due to electron density distribution and HOMO-LUMO analysis.
- Observed large Stokes shifts (up to ~178 nm) and absorption/emission in the near-infrared (NIR) region, tunable by heterocyclic donor choice.
- Theoretical studies accurately predicted experimental HOMO energy trends, highlighting the donor ability of each heterocycle.
Conclusions:
- The isoindigo fluorophore series demonstrates significant potential as a molecular scaffold for efficient fluorescence imaging agents.
- Tuning heterocyclic donor units effectively modulates ICT and shifts optical properties into the NIR region.
- Further modifications with different donor fragments can enhance ICT and optimize NIR optical properties.
