Effect of phthalimide and thieno[3,4-c]pyrrole-4,6,dione acceptors on π-conjugated donor-acceptor-donor monomers: Experimental and theoretical investigations of photophysical and electrochemical properties

• Published in: Tetrahedron 2023-06, Vol.140, p.133473, Article 133473
• Main Authors: Çakal, Deniz, Demir Arabacı, Elif, Yildirim, Erol, Cihaner, Atilla, Önal, Ahmet M.
• Format: Article
• Language: English
• Subjects: Donor-acceptor-donor (D-A-D); EDOT; Phthalimide (PI); Thieno[3,4-c]pyrrole-4,6,dione (TPD); Thiophene
• ISSN: 0040-4020; 1464-5416
• DOI: 10.1016/j.tet.2023.133473

In this study, two novel donor-acceptor-donor monomers were synthesized by coupling a phthalimide (PI) acceptor unit with thiophene (T) and ethylenedioxythiophene (EDOT (E)) donor units. These two novel PI-based monomers, namely 2-(2-ethylhexyl)-4,7-di(thiophen-2-yl)isoindoline-1,3-dione (T-PI) and 4,7-bis(2,3-dihydrothieno[3,4-b] [1,4]dioxin-5-yl)-2-(2-ethylhexyl)isoindoline-1,3-dione (E-PI), were fully characterized via UV–vis and fluorescence spectroscopy as well as electrochemical methods, and the results were directly compared with those of previously synthesized thieno[3,4-c]pyrrole-4,6-dione (TPD)-based analogues to report the results for four classes of monomers. In this regard, the effects of different donor groups and structural modifications in the acceptor unit as changed from PI to TPD have been investigated to reveal the precise effect of the donor and acceptor on the optical and electrochemical properties of the monomers. All monomers exhibits an intramolecular charge transfer band in the low energy region due to strong donor and acceptor interactions. The oxidation and reduction potentials of the monomers are found to vary depending on the strengths of both donor and acceptor units. PI-based monomers show more positive oxidation and less negative reduction potentials than TPD-based analogues. Similarly, thiophene-based analogues reveal the same trend in their oxidation and reduction potentials as compared to EDOT-based analogues. Lastly, PI-based monomers could not undergo polymerization via electrochemical method, unlike TPD-based monomers, since the dihedral angle arising between donor and PI acceptor disturbs molecular planarity significantly, as demonstrated by first principle calculations. [Display omitted] •Two novel donor-acceptor-donor type monomers were synthesized based on phthalimide acceptor with ethyl hexyl side chain.•The strength of phthalimide acceptor was compared with thieno [3,4-c]pyrrole-4,6-dione by using electrochemical and optical methods.•Theoretical calculations were also carried out to solidify experimental data and reveal the structure-property relationships.•Solid state emissive characteristics of monomers hold a great promise for OLED applications.