Charge Transfer States in Stable Neutral and Oxidized Radical Adducts from Carbazole Derivatives

Abstract

In this paper we report the spectral properties of the stable radical adducts 1(•)-3(•), which are formed by an electron donor moiety, the carbazole ring, and an electron acceptor moiety, the polychlorotriphenylmethyl radical. The molecular structure of radical adduct 1(•) in the crystalline state shows a torsion angle of approximately 90° between the phenyl and the carbazole rings due to steric interactions. They exhibit a charge transfer band in the visible range of the electronic spectrum. All of them are chemically oxidized with copper(II) perchlorate to the respective cation species, which show a strong charge transfer band into the near-infrared region of the spectrum. Radical adducts 1(•)-3(•) and the corresponding stable oxidized species 1(+)-3(+) are real organic mixed-valence compounds due to the open-shell nature of their electronic structure. Charge transfer bands of the cation species are stronger and are bathochromically shifted with respect to those of the neutral species due to the greater acceptor ability of the positively charged central carbon atom of the triphenylmethyl moiety. The cationic species 1(+)-3(+) are diamagnetic, as shown by the absence of a signal in the EPR spectrum in acetonitrile solution at room temperature, but they show an intense and unique band in frozen solutions (183 K).

An Enantiopure Propeller‐Like Trityl‐Brominated Radical: Bringing Together a High Racemization Barrier and an Efficient Circularly Polarized Luminescent Magnetic Emitter

“…[1,2] Amongt he organic emittersw ith unpaired electrons, particular attention has been devoted to triphenylmethyl( trityl) radicalbased chlorinatedd erivatives. [3] In additiont ot heir remarkable persistence and chemical stability,t hey also present:( i) high valueso fl uminescence quantum yield (LQY) at long wavelengths, especially when dispersed in rigid hosts; [4][5][6] and (ii)non-linear opticala ctivity, [7] such as high two-photon absorption( 2PA) cross-sections. [8] Even thought hey were first reporteds everald ecades ago, they are, indeed, far from an extinct research field.I nt his sense, different synthetic approachesa re currently being pursued aimingt oo btain higher photostabilitya nd LQY values or red-shifted emissions.…”

Stable All‐Organic Radicals with Ambipolar Charge Transport

“…Values taken from ref. (Cbz‐TTM). [c] Emission spectra of cyclohexane solutions (10 −4 m ) after excitation at λ =450 nm.…”

“…The more intense and broader band in the spectra of the oxidized species is assigned to a photoinduced electron transfer from the carbazole nitrogen atom to the carbocation of the triphenylmethyl moiety of the radical adduct. This band is remarkably shifted to the infrared region of the spectrum with respect to that of the nonsubstituted Cbz‐TTM ( λ =789 nm) . The presence of isosbestic points in all spectra, when going from radical to charged species, proves the stoichiometry and the presence of only two species in all the redox processes.…”

“…The presence of isosbestic points in all spectra, when going from radical to charged species, proves the stoichiometry and the presence of only two species in all the redox processes. This behavior shows the implicit stability of all these species, in accordance with previous insights reported for compounds 1 and 2 …”

Magnetoluminescence in a Photostable, Brightly Luminescent Organic Radical in a Rigid Environment

“…Powder X-ray diffraction (PXRD) analysis was conducted to reveal the effect of doping on the crystal structure of aH-PyBTM ( Figure S3). [11] Thevalue is the highest reported for organic radicals under ambient conditions;t he previous highest value is 64 %f or carbazole-substituted tris(trichlorophenyl)methyl radical in acyclohexane solution, reported by Juliµ et al [22] Ther adiative transition rate (k r )a nd nonradiative transition rate (k nr )ofDope_0.05 were calculated as 6.7 10 6 and 8.3 10 5 s À1 ,r espectively. These results suggest that aH-PyBTM was randomly replaced with PyBTM in the crystal while maintaining the crystal structure in the doping region.…”