TY - JOUR
T1 - Twisted Thiophene-Based Chromophores with Enhanced Intramolecular Charge Transfer for Cooperative Amplification of Third-Order Optical Nonlinearity
AU - Teran, Natasha B.
AU - He, Guang S.
AU - Baev, Alexander
AU - Shi, Yanrong
AU - Swihart, Mark T.
AU - Prasad, Paras N.
AU - Marks, Tobin J.
AU - Reynolds, John R.
PY - 2016/6/8
Y1 - 2016/6/8
N2 - Exploiting synergistic cooperation between multiple sources of optical nonlinearity, we report the design, synthesis, and nonlinear optical properties of a series of electron-rich thiophene-containing donor-acceptor chromophores with condensed π-systems and sterically regulated inter-aryl twist angles. These structures couple two key mechanisms underlying optical nonlinearity, namely, (i) intramolecular charge transfer, greatly enhanced by increased electron density and reduced aromaticity at chromophore thiophene rings and (ii) a twisted chromophore geometry, producing a manifold of close-lying excited states and dipole moment changes between ground and excited states that are nearly twice that of untwisted systems. Spectroscopic, electrochemical, and nonlinear Z-scan measurements, combined with quantum chemical calculations, illuminate relationships between molecular structure and mechanisms of enhancement of the nonlinear refractive index. Experiment and calculations together reveal ground-state structures that are strongly responsive to the solvent polarity, leading to substantial negative solvatochromism (- 102 nm) and prevailing zwitterionic/aromatic structures in the solid state and in polar solvents. Ground-to-excited-state energy gaps below 2.0 eV are obtained in condensed π-systems, with lower energy gaps for twisted versus untwisted systems. The real part of the second hyperpolarizability in the twisted structures is much greater than the imaginary part, with the highest twist angle chromophore giving |Re(γ)/Im(γ)| - 100, making such chromophores very promising for all-optical-switching applications.
AB - Exploiting synergistic cooperation between multiple sources of optical nonlinearity, we report the design, synthesis, and nonlinear optical properties of a series of electron-rich thiophene-containing donor-acceptor chromophores with condensed π-systems and sterically regulated inter-aryl twist angles. These structures couple two key mechanisms underlying optical nonlinearity, namely, (i) intramolecular charge transfer, greatly enhanced by increased electron density and reduced aromaticity at chromophore thiophene rings and (ii) a twisted chromophore geometry, producing a manifold of close-lying excited states and dipole moment changes between ground and excited states that are nearly twice that of untwisted systems. Spectroscopic, electrochemical, and nonlinear Z-scan measurements, combined with quantum chemical calculations, illuminate relationships between molecular structure and mechanisms of enhancement of the nonlinear refractive index. Experiment and calculations together reveal ground-state structures that are strongly responsive to the solvent polarity, leading to substantial negative solvatochromism (- 102 nm) and prevailing zwitterionic/aromatic structures in the solid state and in polar solvents. Ground-to-excited-state energy gaps below 2.0 eV are obtained in condensed π-systems, with lower energy gaps for twisted versus untwisted systems. The real part of the second hyperpolarizability in the twisted structures is much greater than the imaginary part, with the highest twist angle chromophore giving |Re(γ)/Im(γ)| - 100, making such chromophores very promising for all-optical-switching applications.
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U2 - 10.1021/jacs.5b12457
DO - 10.1021/jacs.5b12457
M3 - Article
C2 - 27232098
AN - SCOPUS:84974604008
VL - 138
SP - 6975
EP - 6984
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 22
ER -