Using time-dependent density functional theory (TDDFT) in the design and development of near-IR dopants for liquid crystal device applications

Computational chemistry provides unprecedented opportunities to predict the properties of new materials prior to synthesis. One such important property for optics and photonics applications is optical absorbance. The capability to accurately predict, prior to synthesis, the spectroscopic properties of a series of materials as a function of molecular structure would be an extremely powerful tool in the design and development of new liquid crystal materials, dyes, and dopants intended for use in devices for advanced optics and photonics applications. We have applied time-dependent density function theory (TDDFT) calculations for the first time in the prediction of the absorbance spectra of a series of nickel dithiolene near-infrared (IR) dye complexes with a wide variety of terminal functional groups that are designed to enhance their solubility and stability in liquid crystal host mixtures. The TDDFT method was used to compute the excited-state energies of an existing series of nickel dithiolenes with bulk solvent effects taken into account. Excellent agreement between the theoretical and experimental absorbance maxima was achieved for 14 known dyes with an exceptionally low mean absolute error of 0.033 eV. Calculations conducted on 4 new nickel dithiolene dyes predict that the addition of sulfur atoms to the side chains will increase the maximum absorbance wavelength by up to 160 nm. This improved computational method is being applied to the design and synthesis of highly soluble azobenzene-substituted transition metal dithiolene near-IR dyes that can undergo rapid and reversible photoinduced cis-trans isomerization. Such materials could show substantial promise as photoswitchable near-IR dopants for liquid crystal device applications in telecommunications, sensor protection, nonlinear optics, and laser systems.

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