Controlling charge-transfer properties through a microwave-assisted mono- or bis-annulation of dialkynyl-N-(het)arylpyrroles

Abstract

A selective microwave-assisted mono- and bis-annulation of dialkynyl-N-(het)arylpyrrole derivatives is described. These polycyclic aromatic hydrocarbons (PAHs) have been photophysically and computationally characterized. The mono-annulated systems display interesting charge-transfer properties. By contrast, these properties vanish within the more conjugated bis-annulated compounds.

Efficient Access to Arylated Aza‐ullazines by Regioselective Functionalization of their Pyridine Ring by H−Li Exchange and Electrophilic Substitution

“…Furthermore, we can observe that the low-lying absorption band of most of the compounds (apart compounds 7 b and 7 d) reported herein displays a vibronic character (similar to azaullazine 4) suggesting a local absorption process as discussed in our previous report. [20] We studied the fluorescence properties of the azaullazine derivatives. While the brominated [20] In the cases of compounds 7 b and 7 d, we can notice that their emission pattern is broad indicating typically a charge transfer character, very likely resulting from the presence of the electron-withdrawing effect of the formyl moieties.…”

“…[19] Concomitantly, our research group described the mono-and bisannulation of dialkynyl-N-(het)arylpyrroles promoted by InCl 3 under microwave-assisted heating. [20] Along both reports, it was shown that the introduction of the additional nitrogen atom at position 6 within the ullazine backbone (i. e. aza-ullazine) did not induce significant electronic changes in comparison with the parent ullazine core. Indeed, azaullazine and ullazine display similar absorption and emission properties.…”

Synthesis and Properties of New Multiple TCNE Adducts from Dialkynyl‐N‐(het)arylpyrroles

“…Starting dibrominated materials 1a – c were synthesized following our previously reported procedure and were then subjected to Sonogashira cross‐coupling reaction with N , N ‐dibutyl‐4‐ethynylaniline. Reactions were performed under microwave irradiation in the presence of PdCl 2 (PPh 3 ) 2 /CuI catalytic system.…”

“…2.1 equiv. of alkyne, 10 mol‐% of PdCl 2 (PPh 3 ) 2 and CuI, 35 mol‐% of PPh 3 in Et 2 NH:DMF (2:1, v:v)] . Only the pyridine derivative 2a was obtained in 46 % yield.…”

“…Indeed, optimal charge‐transfer is a critical parameter for the design of sensitizers for solar energy applications. In this context we have recently described the mono‐ and bis‐annulation of dialkynyl‐ N ‐(het)arylpyrroles . These compounds, especially the monoannulated derivatives, have shown interesting optically‐excited charge‐transfer states as opposed to the symmetric bis‐annulated structures that exhibited rather apolar photophysical features.…”