Predicting the substituent effects in the optical and electrochemical properties of N,N′-substituted isoindigos

Abstract

Isoindigo, the structural isomer of the well-known dye indigo, has seen a major revival recently because of the increasing interest of its use as a potential drug core structure and for the development of organic photovoltaic materials. Highly beneficial for diverse applications are its facile synthesis, straightforward functionalisation and the broad absorption band in the visible range. Moreover, its intrinsic electron deficiency renders isoindigo a promising acceptor structure in bulk heterojunction architectures. Here we present new insights into the substituent effects of N-functionalised isoindigos, developing a reliable and fast in silico screening approach of a library of compounds. Using experimental UV–Vis and electrochemical data increased the accuracy of the TD-DFT method employed. This procedure allowed us to accurately predict the optical and electrochemical properties of N-functionalised isoindigos and the elucidation of the relationship between substituent effects and electronic properties. Graphic abstract

Controlling rotary motion of molecular motors based on oxindole

“…N -Arylated motors 7–9 have similar absorption bands, showing almost no effect from functionalisation with either an electron-withdrawing or -donating moiety; presumably, this result is due to the ability of the N -aryl bond to rotate freely, which can disrupt any potential conjugation with the central double bond axle. 45 …”

“…N-Arylated motors 7-9 have similar absorption bands, showing almost no effect from functionalisation with either an electron-withdrawing or -donating moiety; presumably, this result is due to the ability of the N-aryl bond to rotate freely, which can disrupt any potential conjugation with the central double bond axle. 45 Synthesis Motors 1-9 were synthesised in a one-pot Knoevenagel condensation of the corresponding substituted oxindoles with their upper half ketone counterparts, mediated by TiCl 4 as a Lewis acid and N-diisopropylethylamine (DIPEA) as a base. In each case, the motor was isolated exclusively as the stable E isomer, (E S ), in yields varying between 34-73% (Scheme 2).…”

Extended isoindigos as building blocks for developing D–A-type conjugated polymers

“…These copolymers showed excellent semiconducting properties. 40,41 In the past few years, isoindigo-based electron-withdrawing building blocks have been modulated to further enhance their planarity. 42 Two commonly applied strategies to modulate the structure and electronic properties of isoindigo are (i) terminal modification, in which the benzene rings of isoindigo are replaced with other conjugated units, and (ii) center modification, where the conjugated units are introduced into the central part of isoindigo, which can increase the effective conjugated length of isoindigo and avoid steric hindrance.…”

Highly Efficient Oxindole‐Based Molecular Photoswitches

“…[9] Various opportunities to design responsive molecular systems and materials have stimulated the search for novel, broadly applicable photoswitches showing good reversibility and ease of functionalization. Recently, photoswitches based on heterocyclic dyes such as indigo, [10,11] hemithioindigo [12,13] and isoindigo [14] have been investigated, showing robust photochemical switching at red-shifted wavelengths -tackling the challenge of switching within the phototherapeutic window. [3,15,16] Isoindigo is the self-condensation product of indoline-2one, also known as oxindole, which is a privileged scaffold in organic synthesis.…”