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Published on: May 29, 2018
Ultrafast dynamics and computational studies on diaminodicyanoquinodimethanes (DADQs)
Marek Szablewski1, Mark A Fox, Fernando B Dias
1Centre for Materials Physics, Department of Physics, Durham University , South Road, DH1 3LE Durham, United Kingdom.
This study reveals that diaminodicyanoquinodimethanes exhibit fast excited-state decay driven by intramolecular twisting motion. This process is influenced by medium viscosity and functional group size, highlighting unique chromophore characteristics.
Area of Science:
- Organic Chemistry
- Spectroscopy
- Computational Chemistry
Background:
- Diaminodicyanoquinodimethanes are a class of chromophores with unusual properties.
- Understanding their photophysical behavior is crucial for developing new materials.
Purpose of the Study:
- To investigate the structural and photophysical characteristics of three diaminodicyanoquinodimethanes.
- To elucidate the mechanisms governing their excited-state decay dynamics.
Main Methods:
- Carbon-13 Nuclear Magnetic Resonance (NMR) spectroscopy
- Steady-state and ultrafast transient absorption and fluorescence spectroscopies
- Gas-phase electron-averaged relativistic all-electron (GIAO) B3LYP/6-31G* computations with the polarizable continuum model (PCM) solvation model
Main Results:
- Excellent agreement between computed and experimental structural and NMR data.
- Ground-state geometries feature a twisted cationic methine group and an in-plane anionic methine group.
- Significantly upfield-shifted (13)C chemical shifts for the anionic methine carbon compared to TCNQ.
- Fast picosecond excited-state decay dominated by nonradiative processes, dependent on medium viscosity.
- Intramolecular twisting motion, hindered by friction and functional group size, limits excited-state decay.
Conclusions:
- The photophysical behavior of diaminodicyanoquinodimethanes is governed by conformational changes.
- Twisted excited-state conformers are the dominant nonradiative decay pathways.
- Viscosity and functional group size play critical roles in modulating excited-state dynamics.
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