Thiophene‐Containing Pechmann Dyes and Related Compounds: Synthesis, and Experimental and DFT Characterisation

Abstract

Attaching 2-thienyl residues to the Pechmann dye core chromophore (5,5-exo-dilactone situated around a C-C double bond) results in a novel magenta-coloured compound (UV/Vis spectroscopy λ(max) =570 nm in CHCl(3)), which can be rearranged to a yellow 6,6-endo-dilactone (λ(max) =462 nm in CHCl(3)). Single and double amidation results in pronounced redshift in the 5,5-exo series (violet, λ(max) =570 nm and blue, λ(max) =606 nm in CHCl(3), respectively) but pronounced blueshift in the 6,6-endo series (yellow, λ(max) =424 nm and pale yellow bordering on colourless, λ(max) =395 nm in CHCl(3), respectively). Incorporation of a 3-alkyl substituent on the thiophene ring allows for sharp increase of solubility in organic solvents concomitant with fine-tuning of the colour: a redshift in 5,5-exo-dilactones but a blueshift in 5,5-exo-dilactams. DFT computations demonstrate that both lactone classes are planar regardless of the presence of a 3-alkyl group. The lactam derivatives are non-planar: the thiophene-core chromophore dihedral angles increase on going from 5,5-exo to 6,6-endo and from thiophene to 3-alkyl thiophene. Depending on the core heteroatom (O vs. N-alkyl), ring junction (5,5-exo vs. 6,6-endo) and 3-thiophene substituent (H vs. alkyl), two, three, four or six conformers are possible. All of these conformers were characterised by DFT and were found to be very close in energy at both IEFPCM/B3LYP/DGDZVP and SMD/M06/DGDZVP levels of theory. Within each conformer set, the HOMO and LUMO energies were within 0.05 eV and the predicted λ(max) values (TD-DFT) within 10 nm, and this implies low sensitivity of the optical and electronic properties to conformation. Cyclic voltammetry measurements of selected compounds demonstrated good matching to the HOMO and LUMO energies from IEFPCM/B3LYP/DGDZVP computations. M06-2X was the best DFT functional for TD-DFT, giving predicted λ(max) values within about 20 nm.

Experimental and theoretical insight into the electronic properties of 4‐aryl‐5‐arylazo‐3‐cyano‐6‐hydroxy‐2‐pyridone dyes

“…From the Table 3 it can be seen that the obtained results indicate that calculated values of k max obtained by TD-DFT methods are lower than the experimental data. However, despite this deviation, the TD M06-2X method is found to be efficient for evaluating the absorption spectra of conjugated dyes [26,27], and our results are in consistent with this. Also, it is known that this method overestimates energies of electronic transitions [25].…”

Opportunities for Bio-Based Solvents Created as Petrochemical and Fuel Products Transition towards Renewable Resources

“…However given the status of present day technology it is more attractive to obtain 1,4-butanediol from the reduction of bio-based succinic acid, also a fermentation product [ 4 ]. 1,4-Butanediol is a solvent in its own right [ 143 , 144 , 145 ], although in this regard it receives limited attention compared to its application as a monomer for the plastics market [ 146 , 147 ]. It is obvious that starting from the base chemicals results in is a longer synthesis of THF or NMP than the shortcut provided by fermentation to give the intermediate 1,4-butanediol.…”

Interpreting the near-infrared reflectance of a series of perylene pigments

“…The B3LYP functional has been successfully applied in previous studies investigating the structures, electronic properties and spectral characteristics of dye compounds [9], [12], [18], [19]. Therefore, optimized geometries were obtained for all species at the B3LYP/3-21G(d) and B3LYP/6-31G(d) levels of theory.…”