Stable Radical Cations of N,N′‐Diarylated Dihydrodiazapentacenes

Abstract

A series of quinoidal N,N′‐diaryldiaza‐N,N′‐dihydropentacenes (Quino) was prepared in a two‐step reaction, starting from quinacridone. Oxidation of Quino furnishes stable radical cations, isoelectronic to the radical anions of the azaacenes, whereas the dicationic species are isoelectronic to neutral azapentacenes. The spectroscopic properties of the diaryldiazapentacenes and their oxidized mono‐ and dications are equivalent to that of the dianion of tetraazapentacene (TAP), its radical anion and the neutral TAP.

Stable N,N’‐Diarylated Dihydrodiazaacene Radical Cations

“…Recently, we described the preparation and characterization of the N , N’ ‐diaryldiazapentacene Quino and its radical cation Quino +. (see Scheme 1, bottom) [11] . The neutral Quino is unstable in dichloromethane (DCM) with around 20 % absorption intensity loss after 9 h in ambient surroundings, whereas its oxidation product, Quino +.…”

“…The electron-withdrawing -CF 3 groups retard oxidation of the electron-rich N,N'-dihydroazaacenes during column chromatography.T reating 1, 2, and 3 with one equivalent NO + PF 6 À respectively furnished 1 + + C, Scheme1.Preparation of TAP À À C (top), 9 Br 4 TAP À À C (top), 10 and Quino + + C (bottom). [11] Scheme2.Synthetic routes to N,N'-diarylated dihydrodiazaacenes( DDAs) and their corresponding radical cations (DDAs + • ). Conditions: (i)RuPhos Pd G1, RuPhos, tBuOK, toluene, 110 8C, 48 h; (ii)NO + SbF 6 À ,DCM, room temperature,1 2h.…”

Tuning J‐aggregate Formation and Emission Efficiency in Cationic Diazapentacenium Dyes

“…Known N‐quaternized azaacenium salts were synthesized by N‐alkylation of azapentacenes or by introducing aryl groups into the precursors of azaacenes [6] . N,N’ ‐dihydro compounds, which may be obtained by reduction of larger azaacenes, are known for much longer time, and found more stable than longer azaacenes themselves [7] …”

“…[6] N,N'-dihydro compounds, which may be obtained by reduction of larger azaacenes, are known for much longer time, and found more stable than longer azaacenes themselves. [7] Aggregation induced emission (AIE) and AIE-luminogen systems are, at the moment, topics of high interest and impact due to the increment of the emission properties in aggregate systems, which are usually poorly emissive. The occurrence of AIE with a new fluorescence band originating from intermolecular interactions was first reported by Scheibe et al [8] and Jelley [9] who independently observed in 1936 an unusual behavior for pseudoisocyanine chloride (also known as 1,1'diethyl-2,2'-cyanine chloride, PIC chloride) whereas in aqueous solutions the absorption maximum was shifted to lower energies, when compared to the absorption spectrum of the same dye in ethanol, and upon concentration increase (in water), this band became more intense and sharp.…”

“…For similar cationic compounds, e. g., quaternary N-phenyl azaacenium salts in dichloromethane, also small Stokes' shifts and vibronically well-resolved long wavelength absorption bands have been reported. [7] The formation of the vibronically structured, red shifted absorption bands, together with a small Stokes' shift (Δ SS~6 00 cm À 1 , Table 1) and an increase of the fluorescence quantum yield (ϕ F ), indicates the formation of Jaggregates in the poor solvents ACN and DCM (Figure 1). In thin films, although the longest absorption and emission bands are vibronically resolved for D1, the ϕ F value is lower than in poor solvents but higher than in good solvents (Table 2).…”