Synthesis and TD-DFT investigation of arylhydrazonocyclopentadiene dyes

Two approaches for the synthesis of D-A chromophores containing arylhydrazonocyclopentadiene acceptor moieties were developed. The first approach includes the decarboxylative azo coupling reaction between penta (methoxycarbonyl)cyclopentadienyl potassium or sodium and aryldiazonium salts to give products containing four ester groups at the acceptor moiety. The second one includes the reaction of 1,3-dimethoxycarbonyl-4,5diphenylcyclopentadienone with arylhydrazine hydrochlorides into arylhydrazonocyclopentadienes with two ester and two phenyl groups. Both series of compounds were investigated by means of absorption spectroscopy and the solvatochromic behavior of two representatives of each series was investigated in various dielectric environments. Both compounds demonstrated relative independence on the environment although the product with the stronger acceptor part was less stable and exhibited a slight hypsochromic shift in polar media. However, the optical properties of this product were strongly affected by the basicity of the medium due to the deprotonation of the NH-group. Quantum chemical modeling of the synthesized products adsorption spectra using different density functionals has shown that PBE0-D3/def2TZVP is an optimal method (out of three tested) for all compounds both in non-vibrationally-resolved and vibrationally-resolved TD-DFT calculations. Accounting for vibronic coupling in TD-DFT calculations is necessary to achieve good agreement with the experiment for compounds synthesized herein.