Push–Pull‐Type Polychlorotriphenylmethyl Radicals: New Two‐Photon Absorbers and Dyes for Generation of Photo‐Charges

Abstract

Tri(4-iodo-2,3,5,6-tetrachlorophenyl)methane (2) is reported as a general building block for the synthesis of various π-conjugated polychlorotriphenylmethyl (PTM) radicals. Three push-pull-type triphenylamine-substituted PTM radicals with different substitution patterns were prepared and all exhibited intense inter-valence charge-transfer bands and large two-photon absorption (TPA) cross sections. Moreover, increase of solvent polarity also resulted in improved TPA response. The charge-transfer character of the relevant excited states provoked the efficient photo-generation of charges, anions in the PTM and cations in the amine arms, driven by the amphoteric redox character and the small coupling between donor and acceptor.

Luminescent Mono‐, Di‐, and Triradicals: Bridging Polychlorinated Triarylmethyl Radicals by Triarylamines and Triarylboranes

“…While for the monoradical the 2PA cross section follows roughly the lowest energy absorption between 12 000–17 000 cm −1 and the peak at ca. 19 000 cm −1 , the 2PA cross section of the diradical and even more that of the triradical are significantly enhanced, reaching quite impressive 1000–3000 GM, particularly at around 19 000 and 15 500 cm −1 , which contrasts the behavior of recently investigated tris‐(tetrachlorophenyl)methyl radicals . The latter signal shows that the lowest energy absorption band between 12 000–17 000 cm −1 is indeed composed of at least two or three electronic transitions.…”

Design of Perchlorotriphenylmethyl (PTM) Radical‐Based Compounds for Optoelectronic Applications: The Role of Orbital Delocalization

“…In particular, recent works,, have studied the influence of the introduction of donor groups (D) connected to the PTM, which acts as an electron acceptor (A); as a consequence of the strong D‐A character, Intramolecular Electron Transfer (IET) absorption bands appear in the near IR region. However, these IET absorption bands have a very low intensity so that the absorption spectra remain dominated by the intense absorption band associated to the PTM radical (unless in the case of star trisubstituted compound where additional bands at low energy also appear) ,. This typical behaviour has been exemplified for instance in one of our previously synthesized compound where a bivinylenethiophene unit is connected to PTM (see Figure in bright green).…”

“…Moreover, Möller‐Plesset perturbation approaches were also discarded due to problems linked to spin contamination for open‐shell systems such as the PTM radical, which are found to be significantly reduced in the case of Unrestricted DFT approaches. At the DFT level of theory, standard hybrid functionals such as (U)B3LYP have been used to successfully describe the energy levels in PTM radical‐based compounds,, or to calculate Raman spectra ,. However, their use in the description of excited states has been limited,, due to the inherent problems of this functional to deal with the charge‐transfer (CT) character of excited states,, leading to a typical overestimation of their transition energies.…”

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

“…Among the organic emitters with unpaired electrons, particular attention has been devoted to triphenylmethyl (trityl) radical‐based chlorinated derivatives . In addition to their remarkable persistence and chemical stability, they also present: (i) high values of luminescence quantum yield (LQY) at long wavelengths, especially when dispersed in rigid hosts; and (ii) non‐linear optical activity, such as high two‐photon absorption (2PA) cross‐sections . Even though they were first reported several decades ago, they are, indeed, far from an extinct research field.…”