Twisted Diindeno-Fused Dibenzo[a,h]anthracene Derivatives and their Dianions

We report a facile synthesis of diindeno-fused dibenzo[a,h]anthracene derivatives ( DIDBA-2Cl , DIDBA-2Ph , and DIDBA-2H) with different degrees of non-planarity using three substituents (chloro, phenyl, and hydrogen) of various sizes. The planarization of their cores, as evidenced by the decreased end-to-end torsional angles, was confirmed by X-ray crystallography. Their enhanced energy gaps with twisting were investigated by a combination of spectroscopic and electrochemical methods with density functional theory, which showed a transition from singlet open-shell to closed-shell configuration. Moreover, their doubly reduced states, DIDBA-2Ph ²⁻ and DIDBA-2H ²⁻, were achieved by chemical reduction. The structures of dianions were identified by X-ray crystallographic analysis, which elucidated that the electron charging further distorted the backbones. The electronic structure of the dianions was demonstrated by experimental and theoretical approaches, suggesting decreased energy gaps with larger non-planarity, different from the neutral species.     

Preparation and Properties of Cyclopalladated Complexes of Dibenzo[a,c]phenazine and Dibenzo[f,h]quinoxaline with Ethylenediamine

Russian Journal of General Chemistry -     

Indeno[1,2‐b]fluorene‐Based [2,2]Cyclophanes with 4n/4n and 4n/[4n+2] π Electrons: Syntheses,Structural Analyses,and Excitonic Coupling Properties

Indeno[1,2‐b]fluorene‐based [2,2]cyclophanes with 4n/4n and 4n/[4n+2] π‐electron systems were prepared, and their structures were identified by X‐ray crystallography. With short π–π distances around 3.0 Å, [2.2](5,11)indeno[1,2‐b]fluorenophane and its precursor [2.2](5,11)indeno[1,2‐b]fluorene‐6,12‐dionophane exhibit remarkable transannular interactions, leading to their unusual electrochemical and photophysical properties. With the aid of femtosecond transient absorption spectroscopy, the transition from the monomeric excited state to the redshifted H‐type dimeric state was first observed, correlating to the calculated excitonic energy splitting and the steady‐state absorption spectra induced by charge‐transfer‐mediated superexchange interaction.     

Dibenzo[a,c]phenazine: a polarity-insensitive hydrogen-bonding probe

A derivative of phenazine, dibenzo[a,c]phenazine (DBPZ), can be used as a very good hydrogen-bonding probe unlike its parent phenazine molecule. Steady-state absorption and fluorescence studies reveal that DBPZ is completely insensitive to polarity of the medium. However, DBPZ can form a hydrogen bond very efficiently in its first excited singlet state. The extent of this excited-state hydrogen-bond formation depends both on size and on hydrogen-bond donor ability of the solvents. Time-resolved fluorescence studies and theoretical calculations also suggest that this hydrogen-bond formation is much more favorable in the excited state as compared to the ground state. In the excited state, the electron density is pushed toward the nitrogen atoms from the benzene rings, thereby increasing the dipole moment of the DBPZ molecule. Although the dipole moment of DBPZ increases upon photoexcitation, like other polarity probes, the molecule remains fully insensitive to the polarity of the interacting solvent. This unusual behavior of DBPZ as compared to simple phenazine and other polarity probes is due to the structure of the molecule. Hydrogen atoms at the 1 and 8 positions of DBPZ are sterically interacting with a lone pair of electrons on the proximate nitrogen atoms and make both of the nitrogen atoms inaccessible to solvent molecules. For this reason, DBPZ cannot sense the polarity of the medium. However, DBPZ can only sense solvents, those that have hydrogen with some electropositive nature, that is, the hydrogen-bond donating solvents. Hydrogen being the smallest among all elements can only interact with the lone pair of electrons of nitrogen atoms. Thus, DBPZ can act as a sensor for the hydrogen-bond donating solvents irrespective of their dielectrics.     

Synthesis of 5,12-diazadibenz[a,h]anthracene

5, 12-Diazadibenz[a,h]anthracene ( 20 ) was synthesized in 21% overall yield for seven steps. Salient features of the synthesis include the initial, one-step conversion of trans, trans-1,4-bis-(β-nitrovinyl)benzene into 2,2″-dinitro-p-terphenyl by Diels-Alder condensation plus elimination, monocyclization of the derived 2,2″-diformylamino-p-terphenyl to give 8-(2-amino-1-phenyl)-phenanthridine ( 10 ) in the presence of fortified polyphosphoric acid, and accomplishment of a second cyclization step only after reduction of the heteroring in 10 (by means of diisobutyl-aluminum hydride) plus formylation. The 6-methyl and 6,13-dimethyl derivatives of 20 were prepared similarly.     

[40]π Fused and Nonfused Core‐Modified Nonaphyrins: Syntheses and Structural Diversity

The synthesis of fused and nonfused core‐modified 40π nonaphyrins are reported. Spectroscopic and X‐ray structural studies reveal a twisted figure‐eight conformation in the freebase form that is nonaromatic. Structural changes occur, from figure‐eight to open extended conformation, upon protonation, thereby adopting 4nπ Hückel antiaromatic character, which is reflected in spectroscopic and theoretical studies. Such a structural change also induces ring inversions of specific heterocyclic rings by 180°.     

Dibenzo[d,h][1,3,6,7,2]dioxadithiasilonin: Synthesis and characterization

The reaction of 2,4-di-t-butylphenol, 4 , with sulfur monochloride gave the trithiobisphenol 5 rather than the expected dithiobisphenol 7 . The thiol 6 was obtained by the reduction of 5 with zinc under acidic conditions. The dithiobisphenol 7 was prepared by the oxidative coupling of 6 with iodine under alkaline conditions. The dibenzo[d,h][1,3,6,7,2]dioxadithiasilonin 8 was prepared by the reaction of 7 with dichlorodimethylsilane using triethylamine as an acid acceptor. No change was observed in the ¹H nmr spectrum of 8 upon cooling to ?55°, which suggests that the ΔG* for ring inversion is less than the corresponding eight-membered dibenzo[d,g][1,3,2]dioxasilocin and dibenzo[d,g][1,3,6,2]dioxathiasilocin 1 and 2 , respectively. The spectral data and elemental analysis are fully in accord with the nine-membered silonin structure.     

Triplet Emitting C^N^C Cyclometalated Dibenzo[c,h]Acridine Pt(II) Complexes

In a series of Pt(II) complexes [Pt(dba)(L)] containing the very rigid, dianionic, bis-cyclometalating, tridentate C^N^C²⁻ heterocyclic ligand dba^2– (H₂dba = dibenzo[c,h]acridine), the coligand (ancillary ligand) L = dmso, PPh₃, CNtBu and Me₂Imd (N,N’-dimethylimidazolydene) was varied in order to improve its luminescence properties. Beginning with the previously reported dmso complex, we synthesized the PPh₃, CNtBu and Me₂Imd derivatives and characterized them by elemental analysis, ¹H (and ³¹P) NMR spectroscopy and MS. Cyclic voltammetry showed partially reversible reduction waves ranging between −1.89 and −2.10 V and increasing along the series Me₂Imd < dmso ≈ PPh₃ < CNtBu. With irreversible oxidation waves ranging between 0.55 (L = Me₂Imd) and 1.00 V (dmso), the electrochemical gaps range between 2.65 and 2.91 eV while increasing along the series Me₂Imd < CNtBu < PPh₃ < dmso. All four complexes show in part vibrationally structured long-wavelength absorption bands peaking at around 530 nm. TD-DFT calculated spectra agree quite well with the experimental spectra, with only a slight redshift. The photoluminescence spectra of all four compounds are very similar. In fluid solution at 298 K, they show broad, only partially structured bands, with maxima at around 590 nm, while in frozen glassy matrices at 77 K, slightly blue-shifted (~580 nm) bands with clear vibronic progressions were found. The photoluminescence quantum yields Φ_L ranged between 0.04 and 0.24, at 298 K, and between 0.80 and 0.90 at 77 K. The lifetimes τ at 298 K ranged between 60 and 14040 ns in Ar-purged solutions and increased from 17 to 43 µs at 77 K. The TD-DFT calculated emission spectra are in excellent agreement with the experimental findings. In terms of high Φ_L and long τ, the dmso and PPh₃ complexes outperform the CNtBu and Me₂Imd derivatives. This is remarkable in view of the higher ligand strength of Me₂Imd, compared with all other coligands, as concluded from the electrochemical data.     

A Highly Abbreviated Synthesis of Dibenzo[def,p]chrysene and Its 12-Methoxy Derivative, a Key Precursor for the Synthesis of the Proximate and Ultimate Carcinogens of Dibenzo[def,p]chrysene

Dibenzo[def,p]chrysene (DBC) (1), is by far the most mutagenic and toxic polycyclic aromatic hydrocarbon identified. Its metabolic activation leads to trans-11,12-dihydroxy-11,12-dihydro-DBC (2), which is further metabolized to the ultimate metabolite, anti-trans-11,12-dihydroxy-13,14-epoxy-11,12,13,14-tetrahydro-DBC (3), that binds to DNA causing mutations and ultimately tumor induction. We report a facile route for the syntheses of DBC (1) and its 12-methoxy derivative (12-methoxy-DBC) (13), a key intermediate for the synthesis of 2 and 3, using a Suzuki cross-coupling approach.     

Stereoselective syn epoxidation of the dihydrodiols of dibenz[a,h] anthracene and 7-methylbenz[a] anthracene

Epoxidation of the bay region dihydrodiols of the title hydrocarbons affords stereoselectively the corresponding syn diol epoxides rather than the anticipated isomeric anti diol epoxides, indicative of a dominant cis-directing effect of the benzylic vs the allylic axial hydroxyl groups.     

Structural controlled pure metallo-triangular assembly through bisterpyridinyl Dibenzo[b,d]thiophene,Dibenzo[b,d]furan and Dibenzo[b,d]carbazole

A novel family of metallocycles was constructed by a one-pot self-assembly of three analogous bis(terpyridine) ligand monomers L1-L3, having different bent angles, with metal ions (Zn²⁺ or Cd²⁺). The dibenzo[b,d]thiophene-containing ligand L3 assembled with the metal ions to form a single trimer, whereas the dibenzo[b,d]furan-containing ligand L2 and dibenzo[b,d]carbazole-containing ligand L1 formed a mixture of trimers and tetramers. Heteroatoms (N, O, S) significantly contributed to the molecular size of the assemblies, owing to the bent angle of the bis-terpyridines ligands.     

Dibenzo[c,h][1,5]naphthyridinediones as topoisomerase I inhibitors: design, synthesis, and biological evaluation

Dibenzo[c,h][1,5]naphthyridinediones were prepared via a novel synthetic pathway. The compounds were designed as topoisomerase I (Top1) inhibitors based on the indenoisoquinoline series of drugs. The results of biological evaluation demonstrate that, unlike very closely related dibenzo[c,h][1,6]naphthyridinediones, dibenzo[c,h][1,5]naphthyridinediones retain the Top1 inhibitory activity of similarly substituted indenoisoquinolines.     

Dibenzo[b,h][1,4,7]thiadiazonines: examples of a novel ring system

Acetanilides 1a-e react with 1,1'-sulfinylbis(benzotriazole)/trimethylchlorosilane at 45-65 degrees C to form 1,2-di(benzotriazol-1-yl)-2-arylimino-1-ethanethiones 3a-e, while heating the same reagents at 110 degrees C results in dibenzo[b,h][1,4,7]thiadiazonines 5a,c,d, and 6. X-ray crystal structures are reported for three representative examples.     

Synthesis of bisimines of pyrene and dibenz[a,h]anthracene

The preparation of 3b,4a,7b,8a-tetrahydro-4H,8H-pyreno[4,5-b:9,10-b']bisazirine and of 1a,6b,7a,12b-tetrahydro-1H,7H-dibenz[3,4:7,8]anthra[1,2-b:5,6-b']bisazirine is described. The corresponding diepoxides were reacted with sodium azide in aqueous acetone and the mixtures of trans-azido alcohols, so formed, were cyclized by tri-n-butylphosphine.     

Cations and Anions of Dibenzo[a,e]pentalene and Reduction of a Dibenzo[a,e]pentalenophane

Dibenzo[a,e]pentalene (DBP) is a non-alternant conjugated hydrocarbon with antiaromatic character and ambipolar electrochemical behavior. Upon both reduction and oxidation, it becomes aromatic. We herein study the chemical oxidation and reduction of a planar DBP derivative and a bent DBP-phane. The molecular structures of its planar dication, cation radical and anion radical in the solid state demonstrate the gained aromaticity through bond length equalization, which is supported by nucleus independent chemical shift-calculations. EPR spectra on the cation radical confirm the spin delocalization over the DBP framework. A similar delocalization was not possible in the reduced bent DBP-phane, which stabilized itself by proton abstraction from a solvent molecule upon reduction. This is the first report on structures of a DBP cation radical and dication in the solid state and of a reduced bent DBP derivative. Our study provides valuable insight into the charged species of DBP for its application as semiconductor.     

Sono-chemical Synthesis and Mechanism of Dibenz[a,c]anthracene

Planar polycyclic aromatic hydrocarbons have important applications in optoelectronics,environmental chemistry and cancer researches.An improved sono-chemical synthetic procedure of dibenz[a,c]anthrace...