Small Heterocyclic D‐π‐D‐π‐A Push‐Pull Molecules with Complex Electron Donors

Abstract

A large series of small push-pull chromophores based on electron-withdrawing N,N'-dibutylthiobarbituric acid has been designed and successfully synthesized. The electron donating part involves common mesomeric donors such as methoxy, N,N-dimethylamino, N,N-diphenylamino, and piperidin-1-yl groups. Five-membered heteroaromatics, namely thiophene, Nmethylpyrrole, and furan have been employed as electron rich π-linkers and auxiliary donors. Structural analogues bearing aromatic 1,4-phenylene linker were also synthesized for comparison. Fundamental thermal and optoelectronic properties were studied by differential scanning calorimetry, cyclic voltammetry, and absorption spectroscopy. Thorough structureproperty relationships were elucidated, focusing mostly on type of the used π-linker and donor. All experimental conclusions are corroborated by theoretical calculations. The study has shown that a complex donor moiety may be built by properly combining mesomeric and auxiliary donors. Whereas strong mesomeric donor (amino) suppresses the donating effect of auxiliary donors/π-linkers, a combination of weak donor (methoxy) appended at a five-membered heterocycle pronounces the donating ability of the latter.

NIR-II emissive donor–acceptor–donor fluorophores for dual fluorescence bioimaging and photothermal therapy applications

“…67 In the design of the fluorophores, we chose to utilize the alkyl amine donors as they are more effective in their contributions to the electronic structure, specifically to the HOMO, when compared to aryl amine donors. 28,68 The natural transition orbitals (NTO) diagrams, reported in ESI ‡ (Fig. S42), reveal that excitation from the ground-state (S 0 ) to the excited state (S 1 ) involves the transfer of electron density primarily from thiophene spacers to the acceptor with minor contributions from the amine donors themselves.…”

Synthesis, photophysics and two-photon absorption of imidazole-centred tripodal chromophores

“…Aldehyde 1a underwent facile threefold Knoevenagel condensation with activated methylene compounds, such as malonic/acetic acid derivatives 11-12/15-16, indan-1,3-dione 13 and 3-ethylrhodanine 14, which allowed the coupling of complex peripheral withdrawing units of various strengths. 85,86 Target chromophores 1b-6b were isolated with yields ranging from 50 to 70%. Knoevenagel condensations using unsymmetrical C-acids 12 and 14-16 afforded products 2b and 4b-6b with an exclusive stereochemistry.…”

“…[89][90][91] The first oxidation of the rhodanine derivative 4b was recorded as a fully irreversible process due to the preferential oxidation of the sulphur atom instead of the imidazole, which is consistent with our previous studies. 85,86 The first reduction involves peripheral acceptors and, therefore, it was observed as a multielectron irreversible process followed by further reductions. This corresponds to the D-(p-A) 3 arrangement of the investigated chromophores bearing three unequivocal branches (acceptors).…”