2‐ and 2,7‐Substituted para‐N‐Methylpyridinium Pyrenes: Syntheses, Molecular and Electronic Structures, Photophysical, Electrochemical, and Spectroelectrochemical Properties and Binding to Double‐Stranded (ds) DNA

Abstract

Two N‐methylpyridinium compounds and analogous N‐protonated salts of 2‐ and 2,7‐substituted 4‐pyridyl‐pyrene compounds were synthesised and their crystal structures, photophysical properties both in solution and in the solid state, electrochemical and spectroelectrochemical properties were studied. Upon methylation or protonation, the emission maxima are significantly bathochromically shifted compared to the neutral compounds, although the absorption maxima remain almost unchanged. As a result, the cationic compounds show very large apparent Stokes shifts of up to 7200 cm−1. The N‐methylpyridinium compounds have a single reduction at ca. −1.5 V vs. Fc/Fc+ in MeCN. While the reduction process was reversible for the 2,7‐disubstituted compound, it was irreversible for the mono‐substituted one. Experimental findings are complemented by DFT and TD‐DFT calculations. Furthermore, the N‐methylpyridinium compounds show strong interactions with calf thymus (ct)‐DNA, presumably by intercalation, which paves the way for further applications of these multi‐functional compounds as potential DNA‐bioactive agents.

Methyl Viologens of Bis‐(4’‐Pyridylethynyl)Arenes – Structures, Photophysical and Electrochemical Studies, and their Potential Application in Biology

“…On the other hand, both the absorption of 3 at 464 nm ( ϵ =20900 M −1 cm −1 ) and emission at 472 nm are comparatively red‐shifted. The absorption and emission spectra of all of the dications are red‐shifted compared to their neutral counterparts, as was observed earlier for the pyrene compounds [16] . Compound 1M , 2M and 3M absorb at 368 nm ( ϵ =62800 M −1 cm −1 ), 357 nm ( ϵ =51000 M −1 cm −1 ) and 510 nm ( ϵ =33800 M −1 cm −1 ), respectively, while their emissions occur at 427 nm, 399 nm, and 578 nm, respectively.…”

“…Solid state emissions for 3 (590 nm) and 3M (649 nm) are bathochromically shifted compared to their emission in solution. All of the neutral compounds ( 1 – 3 ) show very small Stokes shifts (360–700 cm −1 ), while the dications ( 1M – 3M ) show larger Stokes shifts (2300–3870 cm −1 ), which are, nevertheless, smaller than those of the analogous pyrene compounds [16] . Compound 3 has the highest quantum yield of 0.93 in MeCN, and essentially unity (1.0) in CH 2 Cl 2 .…”

“…The 2‐substituted and 2,7‐disubstituted pyridyl‐pyrene compounds were further methylated, and a detailed study including their structures, photophysical, electrochemical properties, and their interaction with DNA was reported with in‐depth theoretical calculations. We found that the 2,7‐disubstituted N ‐methylated compound, an acceptor‐π‐acceptor system, can act not only as an oxidizing agent, but also an effective bio‐active compound, signifying its utility as a multi‐functional material [16] . It is worth mentioning that this compound underwent either to a two‐electron reduction or to two closely spaced consecutive one‐electron reductions, leading to the formation of the neutral species, without producing the intermediate radical cation.…”

“…We also have shown that upon methylation, the dihedral angle between the pyridinium ring and the central aromatic moiety approaches zero [16] . Such a flat aromatic structure can facilitate its stacking with nucleobases and consequently intercalation into DNA/RNA [17] .…”

Methylthiophene terminated D–π–D molecular semiconductors as multifunctional interfacial materials for high performance perovskite solar cells

“…For MT1, the S0 -S1 transition has an appreciable oscillator strength, corresponding to the absorption at 374 nm in experimental spectra. For MT2, the S0 -S1 transition exhibits a very small oscillator strength, suggesting that it's transition dipole forbidden, 54,55 which is in agreement with the weak absorption between 420 and 490 nm observed experimentally. The optical energy gaps (E g ) estimated from the onset wavelength of the UV-vis spectrum are 2.90 and 2.56 eV for MT1 and MT2 respectively, which matches well with the calculation results (Fig.…”