Side-chain engineering of oligothiophene-extended triphenylamines for stable radical cations with NIR-II to NIR-III absorption

Treatment of bis-1,3-dithiole with 1 equiv. of chlorine affords a very stable radical cation which is amenable to full chemical and spectroscopic characterization.

One- and two-electron oxidation of a digallene stabilized by an N-heterocyclic carbene afforded the first stable gallium-based radical cation and dication salts, respectively. Structural analysis and theoretical calculations reveal that the oxidation occurs at the Ga=Ga double bond, leading to removal of π electrons of the double bond and a decrease of the bond order. The spin density of the radical cation mainly locates at the two gallium centers as demonstrated by EPR spectroscopy and theoretical calculations. Moreover, the reactivity of the radical cation salt toward nBu3 SnH and cyclo-S8 was studied; a digallium-hydride cation salt containing a Ga-Ga single bond and a gallium sulfide cluster bearing an unprecedented ladder-like Ga4 S4 core structure were obtained, respectively.

This thesis focuses on the synthesis and characterization of azaacenes and stable azaacene radical cations.
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\nIn Chapter 2, the synthesis, properties, and solid state X-ray single crystal structures of two new rubrene derivatives, viz diazarubrene DAR and tetraazarubrene TAR, are reported. Both the azarubrenes are more oxidatively stable than rubrene itself and show similar optical properties but differ in their crystal packing from that of rubrene.
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\nIn Chapter 3, the synthesis, property evaluation, and single crystal X-ray structures of 5,7,12,14-tetrafunctionalized diazapentacenes (TDAPs) are presented. Starting from tetrabromo-N,N’-dihydrodiazapentacene, Pd-catalyzed coupling gave the precursors that furnished, after further redox reactions, the diazapentacenes as stable crystalline materials. The performance of the tetraphenylated compound as n-channel semiconductor was evaluated in organic field-effect transistors.
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\nIn Chapter 4, a series of quinoidal N,N’-diaryl-N,N’-dihydrodiazapentacenes (Quinos) were prepared in a two-step reaction, starting from quinacridone. Oxidation of Quinos furnished 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.
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\nIn Chapter 5, three stable N,N’-diarylated dihydroazaacene radical cations (DDAs+·) were prepared by oxidation of neutral N,N’-diarylated dihydroazaacenes (DDAs), synthesized through Buchwald-Hartwig aminations of aryl iodides with N,N’-dihydroazaacenes employing a palladium catalyst. The spectroscopic properties, single crystal X-ray structures, and DFT calculations of these neutral compounds and their radical ions were systematically investigated. All the radical cations are stable and their absorption spectra in dichloromethane remained unchanged in ambient conditions for at least 24 hours.

Stable radical cations of dimeric amino acid derivatives of tryptophan and tyrosine were generated by collision-induced dissociation of [Cu(II)(diethylenetriamine)(amino acid derivative)2]*2+. The yields of the dimer radical cations were dependent on both the auxiliary ligand and the tryptophan or tyrosine derivatives used. Amino acid derivatives with an unmodified carboxylic acid group did not generate dimer radical cations. For the amino acid derivatives Ac-Trp-OMe and Ac-Trp-NH2 (Ac is N-acetyl; OMe and NH2 are the methyl ester and amide modifications of the C-terminal carboxylic group), no auxiliary ligand was required for generating the dimer radical cations. Collision-induced dissociation of the [Cu(II)(amino acid derivative)4]*2+ precursor generated the dimer radical cation [(amino acid derivative)2]*+. Stabilizing interactions, most likely involving hydrogen bonding, between the two amino acid derivatives are proposed to account for observation of the dimer radical cations. Dissociation of these ions yields protonated or radical cationic amino acid derivatives; these observations are consistent with the expectation of proton competition between monomeric units, whose proton affinities were calculated using density functional theory.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTA remarkably stable organic radical cation: the distonic isomer of the unstable radical cation of dimethyl propyl phosphateL. K. Marjatta Kiminkinen, Krista G. Stirk, and Hilkka I. KenttamaaCite this: J. Am. Chem. Soc. 1992, 114, 6, 2027–2031Publication Date (Print):March 1, 1992Publication History Published online1 May 2002Published inissue 1 March 1992https://pubs.acs.org/doi/10.1021/ja00032a015https://doi.org/10.1021/ja00032a015research-articleACS PublicationsRequest reuse permissionsArticle Views273Altmetric-Citations24LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts

Solution-phase synthesis of long rylenes remains challenging due to their strong tendency to aggregate. Introducing backbone twist can reduce aggregation and simultaneously generate potential helical chirality. Herein, we report a series of rylene molecules-up to octarylene-bearing both odd- and even-numbered naphthalene units and multiple n-butoxy substituents at the bay/ortho positions, synthesized via stepwise cross-coupling followed by controlled oxidative dehydrogenation. Peri-attached 4-(trifluoromethyl)phenyl groups further stabilize the extended scaffolds. The electron-rich n-butoxy groups not only induce pronounced backbone twisting but also impart strong electron-donating character. X-ray crystallography reveals that long rylenes with two or more bay- tetra(n-butoxy) motifs adopt alternating P/M helicity rather than a homochiral helical conformation. These molecules exhibit clear length-dependent optical and electrochemical properties, with absorption and emission spanning the visible to near-infrared region. Their electron-rich nature enables facile formation of stable radical cations and dications. Solid-state structures of representative radical cations show distinct intermolecular stabilizing interactions, while 1H NMR and ACID analyses of the dications reveal a systematic evolution from local to global aromaticity.

Solution‐phase synthesis of long rylenes remains challenging due to their strong tendency to aggregate. Introducing backbone twist can reduce aggregation and simultaneously generate potential helical chirality. Herein, we report a series of rylene molecules–up to octarylene—bearing both odd‐ and even‐numbered naphthalene units and multiple n ‐butoxy substituents at the bay/ortho positions, synthesized via stepwise cross‐coupling followed by controlled oxidative dehydrogenation. Peri ‐attached 4‐(trifluoromethyl)phenyl groups further stabilize the extended scaffolds. The electron‐rich n ‐butoxy groups not only induce pronounced backbone twisting but also impart strong electron‐donating character. X‐ray crystallography reveals that long rylenes with two or more bay‐ tetra( n ‐butoxy) motifs adopt alternating P / M helicity rather than a homochiral helical conformation. These molecules exhibit clear length‐dependent optical and electrochemical properties, with absorption and emission spanning the visible to near‐infrared region. Their electron‐rich nature enables facile formation of stable radical cations and dications. Solid‐state structures of representative radical cations show distinct intermolecular stabilizing interactions, while 1 H NMR and ACID analyses of the dications reveal a systematic evolution from local to global aromaticity.

We demonstrated the electrochromism of photochromic radical complexes containing triaryl imidazole: fast photoswitchable pentaarylbiimidazole (PABI) and the phenoxyl-imidazolyl radical complex (PIC). Cyclic voltammetry and spectroelectrochemistry revealed that PABI and PIC generate the highly stable radical cation by one-electron oxidation accompanied by a color change from colorless to green. The stability of the radical cation is strongly affected by the dihedral angle between the imidazole ring and the phenyl ring at the 2-position of the imidazole ring.

The cyclic π-conjugated hydrocarbons fully annelated with a rigid u-framework such as bicyclo [2.2.2] octene (abbreviated as BCO) are expected to have unusual properties due to steric as well as electronic effects of the surrounding σ-framework. In order to clarify such properties, a series of sixto eight-membered ring π-systems and a spirocyclopentadienyl compound having BCO frameworks have been synthesized utilizing reductive cyclization of terminal dibromides of BCO oligomers as the key reaction. These hydrocarbons are found to be redox-active, with positively charged species particularly stabilized owing to both inductive and σ-π- conjugative effects. The annelation with rigid bicycloalkene is also advantageous in kinetic stabilization and “Bredt's-rule protection” of the species otherwise too unstable to observe under ordinary conditions. Some of the results to be noted are as follows. The benzene having three BCO units is oxidized to the stable cation radical : the tropylium ion having three BCO units exhibits the extraordinary stability with the pKR+ value of 13.0 : the cyclooctatetraene (COT) with four BCO units affords the first example of a stable COT cation radical : this cation radical is further oxidized to the first COT dication which is stable at room temperature : a polycyclic BCO pentamer having spiro-cyclopentadienyl rings demonstrates the presence of the σ-π interaction by remarkable elongation of the interacting σ-bond.

meso-Trimesityl-substituted [20]smaragdyrin freebase was synthesized by p-toluenesulfonic acid catalyzed reaction of 5-mesityldipyrromethane and 2,14-dibromodipyrrin in an improved yield of 63 %. Unexpectedly, treatment of the [20]smaragdyrin freebase with BF3 ⋅ OEt2 and triethylamine (TEA) gave a stable radical species, in which the BF2 unit is coordinated at the tripyrrin site, probably by ready release of a hydrogen atom of a [22]smaragdyrin BF2 complex. Similar treatment of [22]smaragdyrin free base produced another [22]smaragdyrin BF2 complex, in which the BF2 unit is coordinated at the dipyrrin site. The tripyrrin site coordinated neutral radical was oxidized with AgSbF6 to give a stable antiaromatic cation; this was reduced with NaBH4 to its 22π congener, which was easily oxidized back to the neutral radical in the air and rearranged to thermodynamically stable dipyrrin site coordinated [22]smaragdyrin BF2 complex upon treatment with BF3 ⋅ OEt2 and TEA. Further, the dipyrrin site coordinated [22]smaragdyrin BF2 complex was similarly oxidized to a stable neutral radical and a stable cation in a stepwise manner. This work demonstrates a rare ability of smaragdyrin BF2 complexes to exist in multiple redox states, particularly forming a stable neutral radical by facile release of a hydrogen atom.

The synthesis of organic radicals continues to garner significant interest due to their fascinating optical, electronic, and magnetic properties. Moreover, the growing demand for chemically stable organic radicals is driven by the rapid expansion of the market for electronic devices utilizing organic semiconductors. In this context, the development of multifaceted approaches for the design of stable organic radicals is of great importance. In this work, we introduce a strategy for generating stable radical cations of diketopyrrolopyrroles (DPP) by modulating the substitution pattern of the electron-donating carbazole substituent. Using electronic, spin resonance, and vibrational spectroscopies, supported by density functional theory, we carefully investigated the electronic structures and chemical stability of the DPP radical cations. Our findings demonstrate that the position of electron-rich heteroatoms and the presence of Clar's aromatic sextets in donor moieties play a pivotal role in enhancing the chemical stability of DPP radical cations.

Stable aryl-armed dihydrophenazines-based radicals

A highly stable molecular radical cation (RC) derived from ethylenedioxy thiophene (EDOT) is effectively utilized for the p-doping of poly-3-hexylthiophene (P3HT), an organic semiconductor. The success of this process is due to efficient electron transfer from the highest occupied molecular orbital band of P3HT to the singly unoccupied molecular orbital of the radical cation species. Confirmation of the doping is experimentally confirmed through UV-vis-NIR absorption spectroscopy and electron spin resonance spectroscopy. The ability to dope the conjugated polymers PBTTT and PTB7 is also spectroscopically confirmed. An increase in work-function of P3HT upon doping is observed due to electron transfer from P3HT to the radical cation with a concomitant decrease in the Fermi energy of P3HT. Impedance and four point probe analysis showed that the doped polymer films exhibited a significant decrease in resistance compared to the pristine films. This work presents the first use of a stable, easily synthesized EDOT-based radical cation as a molecular p-dopant for conjugated polymers, offering a novel and broadly applicable alternative to traditional dopants such as F4TCNQ.

Radical Ions The synthesis and characterization of stable iron pentacarbonyl radical cation salts is reported by Ingo Krossing et al. in their Communication (e202204080).

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTChemical and electrochemical oxidation of CpRe(PAr3)2H2 complexes to give stable 17-electron radical cations. Disproportionation to diamagnetic species via electron-transfer catalysisMichael R. Detty and William D. JonesCite this: J. Am. Chem. Soc. 1987, 109, 19, 5666–5673Publication Date (Print):September 1, 1987Publication History Published online1 May 2002Published inissue 1 September 1987https://doi.org/10.1021/ja00253a017RIGHTS & PERMISSIONSArticle Views255Altmetric-Citations25LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts