A decade ago Aprahamian and coworkers reported their accidental discovery of a BF2-coordinated azo dye which photoisomerizes at much longer wavelengths than conventional azo dyes. In a second paper they used electron donors on the phenyl moiety to tune spectroscopic properties of these dyes before returning to their intended hydrazone chemistry. In these works, very brief mention of TD-DFT computation of these dyes was made. An initial effort incorporate these dyes into photoresponsive polymeric materials, unsuccessful to date, yielded improved synthetic methods, the ability to functionalize the quinoline moiety of the dye, and preliminary evidence that these changes impacted the dyes’ spectra at least as much as substituents on the phenyl moiety the Aprahamian group had explored. The Gillmore undergraduate research group at Hope College has recently launched a newly funded project to make and study a library of these dyes. We have proposed several hundred possible targets, far more than we could ever synthesize. In order to focus efforts on dyes of particular interest, we proposed to use TD-DFT computations to predict the absorbance spectra of the dyes. However the single computational prediction of the parent dye reported by Aprahamian & Hughes appears to have been a fluke as their method is unsuccessful even for any of their own derivatives, much less our new quinoline-substituted variants. After a fruitless year attempting to vary functionals, basis sets, solvent models, and other parameters, to achieve quantitatively accurate TD-DFT result, we have subsequently developed a method to use TD-DFT computations of known dyes correlated to experimental data to afford a fit that allows us to use a precise but inaccurate combination of functional, basis set, and solvent model to accurately predict the long wavelength absorbance maxima of both known and novel dyes. We are currently applying statistical methods to improve this correlation.

Predicting UV-Vis-NIR absorbance spectra of novel long-wavelength azo dyes

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ACS Fall 2022

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