Highly Fluorescent Dyes Containing Conformationally Restrained Pyrazolylpyrene (Pyrazoolympicene) Chromophore

The triflic-acid-promoted cyclization of 1-phenyl-3-(pyren-1-yl)-1H-pyrazole-4-carbaldehyde afforded a mixture of 9-phenyl-7,9-dihydropyreno (10,1-fg)indazole and 9-phenylpyreno(10,1-fg)indazole-7(9H)-one, readily separable by column chromatography. Both products contained a rigid six-ringed pyrazoolympicene backbone and exhibited bright fluorescence in chloroform solution and a weak fluorescence in the solid state. DFT and TD DFT calculations revealed that the lowest excited state (S1) of these compounds is populated via HOMO →LUMO π-π * transition. Furthermore, the synthesized compounds behaved as weak bases and their emission spectra showed substantial changes upon protonation. Therefore, they may be of interest for sensing of strongly acidic fluorophore environments

Highly Fluorescent Dyes Containing Conformationally Restrained Pyrazolylpyrene (Pyrazoolympicene) Chromophore

The triflic-acid-promoted cyclization of 1-phenyl-3-(pyren-1-yl)-1H-pyrazole-4-carbaldehyde afforded a mixture of 9-phenyl-7,9-dihydropyreno (10,1-fg)indazole and 9-phenylpyreno(10,1-fg)indazole-7(9H)-one, readily separable by column chromatography. Both products contained a rigid six-ringed pyrazoolympicene backbone and exhibited bright fluorescence in chloroform solution and a weak fluorescence in the solid state. DFT and TD DFT calculations revealed that the lowest excited state (S1) of these compounds is populated via HOMO →LUMO π-π * transition. Furthermore, the synthesized compounds behaved as weak bases and their emission spectra showed substantial changes upon protonation. Therefore, they may be of interest for sensing of strongly acidic fluorophore environments

Regioselective (thio)carbamoylation of 2,7-di-tert-butylpyrene at the 1-position with iso(thio)cyanates

It has been found that 2,7-di-tert-butylpyrene reacts with aliphatic iso(thio)cyanates in the presence of trifluoromethanesulfonic acid to exclusively afford the corresponding 1-substituted (thio)amides in high yields. For aromatic iso(thio)cyanates the reaction is less regioselective, although substitution at the 1-position prevails. For ethoxycarbonyl isothiocyanate, apart from the 1-substituted thioamide, 1,8-disubstituted thioamide and 2,7-di-tert-butylpyrene-1-carbonitrile are formed (especially at longer reaction times)

Electrophile-Dependent Reactivity of Lithiated <i>N</i>-Benzylpyrene-1-Carboxamide

In this paper, we describe the lithiation of N-benzylpyrene-1-carboxamide with RLi-TMEDA. We found that the reaction outcome strongly depends on the electrophile used in the quenching step. The electrophile can be introduced at either the benzylic position or at the C-2 position in the pyrene nucleus. Furthermore, when H+ was used as the quencher, the product of the intramolecular carbolithiation of the pyrene K-region was formed. Dehydrogenation of the obtained compound with DDQ allowed the synthesis of a novel nitrogen polycyclic compound with an aza-benzo[c,d]pyrene (azaolympicene) skeleton. Attempts to extend the reaction scope to the amides substituted in the phenyl ring 8a and 8b gave an unexpected result. The reaction of both compounds with BuLi gave 1-valerylpyrene (9) in good yield. Photophysical properties, including absorption spectra, emission spectra and quantum yields of the emission of selected products, were studied and discussed

Polycyclic Aromatic <i>N</i>‑Ethoxycarbonyl Thioamide <i>S</i>‑Oxides and Their Triflic Acid Promoted Cyclization to Fluorescent Thiophene Imine-Fused Arenes

We present the synthesis of a series of polycyclic aromatic-<i>N</i>-ethoxycarbonylthioamide <i>S</i>-oxides and their triflic acid-promoted cyclization to thiophene imine-fused arenes having 2<i>H</i>-naphtho­[1,8-<i>bc</i>]­thiophen-2-imine, 3<i>H</i>-pyreno­[10,1-<i>bc</i>]­thiophen-3-imine, 4<i>H</i>-pyreno­[1,10-<i>bc</i>]­thiophen-4-imine, 3<i>H</i>-pyreno­[10,1-<i>bc</i>]­thiophen-3-imine, 4<i>H</i>-pyreno­[1,10-<i>bc</i>]­thiophen-3-imine, 3<i>H</i>-pyreno­[10,1-<i>bc</i>]­thiophen-3-imine, and 4<i>H</i>-peryleno­[3,4-<i>bc</i>]­thiophen-4-imine cores. The proposed reaction mechanism involves the intermediacy of a novel type of electrophilic sulfur species, namely protonated iminosulfenic acid or iminosulfenium cations. These species may attack the <i>peri</i>- or <i>ipso</i>-position of the arene, leading in some cases to regioisomeric products. The reaction affords in high yields novel polycyclic fluorophores emitting in the range of 500–606 nm with quantum yields of 0.025–0.64. Comparison with the parent arenes reveals that the fused iminothiophene moiety brings about significant bathochromic shifts of the absorption and emission bands

Polycyclic Aromatic <i>N</i>‑Ethoxycarbonyl Thioamide <i>S</i>‑Oxides and Their Triflic Acid Promoted Cyclization to Fluorescent Thiophene Imine-Fused Arenes

We present the synthesis of a series of polycyclic aromatic-<i>N</i>-ethoxycarbonylthioamide <i>S</i>-oxides and their triflic acid-promoted cyclization to thiophene imine-fused arenes having 2<i>H</i>-naphtho­[1,8-<i>bc</i>]­thiophen-2-imine, 3<i>H</i>-pyreno­[10,1-<i>bc</i>]­thiophen-3-imine, 4<i>H</i>-pyreno­[1,10-<i>bc</i>]­thiophen-4-imine, 3<i>H</i>-pyreno­[10,1-<i>bc</i>]­thiophen-3-imine, 4<i>H</i>-pyreno­[1,10-<i>bc</i>]­thiophen-3-imine, 3<i>H</i>-pyreno­[10,1-<i>bc</i>]­thiophen-3-imine, and 4<i>H</i>-peryleno­[3,4-<i>bc</i>]­thiophen-4-imine cores. The proposed reaction mechanism involves the intermediacy of a novel type of electrophilic sulfur species, namely protonated iminosulfenic acid or iminosulfenium cations. These species may attack the <i>peri</i>- or <i>ipso</i>-position of the arene, leading in some cases to regioisomeric products. The reaction affords in high yields novel polycyclic fluorophores emitting in the range of 500–606 nm with quantum yields of 0.025–0.64. Comparison with the parent arenes reveals that the fused iminothiophene moiety brings about significant bathochromic shifts of the absorption and emission bands

Friedel–Crafts-type reaction of pyrene with diethyl 1-(isothiocyanato)alkylphosphonates. Efficient synthesis of highly fluorescent diethyl 1-(pyrene-1-carboxamido)alkylphosphonates and 1-(pyrene-1-carboxamido)methylphosphonic acid

Friedel–Crafts-type reaction of pyrene with diethyl 1-(isothiocyanato)alkylphosphonates promoted by trifluoromethanosulfonic acid afforded diethyl 1-(pyrene-1-carbothioamido)alkylphosphonates in 83–94% yield. These compounds were transformed, in 87–94% yield, into the corresponding diethyl 1-(pyrene-1-carboxamido)alkylphosphonates by treatment with Oxone®. 1-(Pyrene-1-carboxamido)methylphosphonic acid was obtained in a 87% yield by treating the corresponding diethyl phosphonate with Me3Si-Br in methanol. All of the synthesized amidophosphonates were emissive in solution and in the solid state. The presence of a phosphonato group brought about an approximately two-fold increase in solution fluorescence quantum yield in comparison with that of a model N-alkyl pyrene-1-carboxamide. This effect was tentatively explained by stiffening of the amidophosphonate lateral chain which was caused by the interaction (intramolecular hydrogen bond) of phosphonate and amide groups. The synthesized phosphonic acid was soluble in a biological aqueous buffer (PBS, 0.01 M, pH 7.35) and was strongly emissive under these conditions (λem = 383, 400 nm, τ = 18.7 ns, ΦF > 0.98). Solid-state emission of diethyl 1-(pyrene-1-carboxamido)methylphosphonate (λmax = 485 nm; ΦF = 0.25) was assigned to π–π aggregates, the presence of which was revealed by single-crystal X-ray diffraction analysis

Multi‐Directional Mechanofluorochromism of Acetyl Pyrenes and Pyrenyl Ynones

International audienceA series of acetyl pyrenes and pyrenyl ynones with and without tert-butyl groups showed distinct mechanofluorochromism (MFC). Four pairs of polymorphic solids were found out of six compounds and interestingly, each of them showed hypsochromic, bathochromic or off-to-on MFC. The MFC properties were rationalized by categorizing the packing schemes into herringbone, sandwich, beta and gamma motifs depending on the relative contributions of C⋯C (or π-π) against C⋯H contacts. The bulky tertbutyl and trimethylsilyl groups served not only to reduce the number of aggregation patterns but also to prohibit the complete back reactions in solid state. Our results suggest that the simple pyrene derivatives may be promising candidates for a novel group of mechanically-sensitive materials