Planar, Fluorescent Push–Pull System That Comprises Benzofuran and Iminocoumarin Moieties

Abstract

Previously unknown, vertically linked heterocycles comprised of benzofuran and iminocoumarin moieties have been synthesized directly from 1,5-dibenzoyloxyanthraquinone and arylacetonitriles via double Knoevenagel condensation followed by formal HCN elimination. The structural assembly of fully conjugated, electron-rich benzofuran and electron-deficient iminocoumarin is responsible for the strongly polarized nature of these heterocycles which translates into their polarity-sensitive fluorescence.

π‐Conjugated Organic–Inorganic Hybrid Photoanodes: Revealing the Photochemical Behavior through In Situ X‐Ray Absorption Spectroscopy

“…It is worth emphasizing, however, that the absorption of dye 1 is bathochromically shifted by 20 nm compared to that of dye 2 , which underlines a better electronic communication between the aryl substituents and the core in the case of the former compound, due to a smaller dihedral angle between core and substituents. On the other hand, the λ max of the non‐symmetrical dye 4 is located at 451 nm, bathochromically shifted of about 50 nm compared to the spectra of previously reported analogous compounds bearing an iminocoumarin moiety . This is related to the increase in electron‐donating character of benzofuran, which is now weakly conjugated with an electron‐rich indole moiety.…”

“…[15,16,17] This property can, in principle, increase charge mobility after photo-annealing, whereas, at the same time, soluble precursor dyes can be deposited from solutions. [18] The structure of dye 4 was confirmed by 1 Ha nd 13 CNMR spectroscopy and MS. In particular, to ensure ar easonable electronic communication, we focusedo nh eterocyclic substituents bearing five-membered rings.…”

“…However, the reaction of 5 with ethyl 1‐ tert ‐butyloxycarbonyl‐indole‐3‐carboxylate led to the unexpected formation of heterocycle 4 , comprised of vertically linked benzofuran and coumarin moieties. This process resembles the formation of the furo[4′,3′,2′:4,5]naphtho[1,2,3‐ de ]chromen‐7‐imine skeleton from aryl acetonitriles and compound 5 , previously described by us . The structure of dye 4 was confirmed by 1 H and 13 C NMR spectroscopy and MS.…”

“…In particular, to ensure ar easonable electronic communication, we focusedo nh eterocyclic substituents bearing five-membered rings. [18] This is related to the increasei ne lectron-donating charactero fb enzofuran, which is now weakly conjugated with an electron-rich indole moiety. [15,16] The doubleK noevenagel condensation of 1,5-di-(benzoyloxy)anthraquinone 5 with variouse ster derivatives of thiophene, benzothiophene, and indole was performed (Scheme 1).…”

The Coumarin‐Dimer Spring—The Struggle between Charge Transfer and Steric Interactions

“…The obvious key elements to the construction of such structures are the push–pull π‐conjugated building blocks . Such molecules possessing high dipole moments are a key class of dye widely employed both in practical applications as well as in various types of research . Their popularity stems from the appreciable combination of optical properties, such as high fluorescence quantum yield, large Stokes shift, and polarity‐sensitive fluorescence .…”