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1,4-Dioxa-7,13-dithia-10-azacyclopentadecane (AT215C5) or 1,4,7,10-tetraoxa-13-azacyclopentadecane (A15C5) were attached as metal-ion-binding receptor units at the ortho or para positions of the 9-amino-N-phenylbenzo[b]quinolizinium chromophore. The addition of Hg2+ or Mg2+ to the para isomers of the AT215C5–quinolizinium or A15C5–quinolizinium conjugate, respectively, led to a blueshift of the absorption maxima of each compound because of the reduced donor ability of the complexed amino group. In contrast, the addition of Hg2+ to a solution of the ortho-AT215C5–quinolizinium conjugate in H2O/MeOH mixtures induced a significant redshift (ca. 50 nm) of the absorption maximum and enabled the photometric discrimination between Hg2+ and competing thiophilic cations, such as Ag+ or Pb2+, because the latter, as well as other competing metal ions, did not induce such an effect. It is proposed that the Hg2+-induced redshift originates from the complexation of Hg2+ by the thiaazacrown ether followed by deprotonation of the secondary 9-amino substituent of the aminobenzoquinolizinium unit. The resulting amide functionality increases the donor–acceptor interplay leading to the redshifted absorption and also coordinates to Hg2+ to form a lariat ether type complex. A similar effect was observed upon the addition of Mg2+ to the 9-amino-N-phenylbenzo[b]quinolizinium derivative with the A15C5 unit in the ortho position; however, this effect was only operative in aprotic solvents, e.g. CH3CN, and with less than 1 mol-equiv. of Mg2+.

Two isomeric acridizinium–adenine conjugates, along with three model compounds (i.e. two 9-(N-alkylcarboxamido)acridizinium salts and one 9-{N-[(dimethylamino)alkyl]carboxamido}acridizinium salt) were prepared from the corresponding carboxyacridizinium salts. The interaction of these compounds with calf thymus DNA was studied by spectrophotometric and viscosimetric titrations, LD spectroscopy, and thermal DNA denaturation experiments. Both of the acridizinium–adenine conjugates and the N-alkylcarboxamides intercalate into calf thymus DNA with moderate affinity [K ≈ 104M–1 (DNA concentration in bp)]. In contrast, the N-[3-(dimethylamino)propyl]-substituted carboxamide exhibits a significantly higher binding constant under identical conditions (K ≈ 105M–1). The association of the acridizinium derivatives with abasic-site containing DNA was assessed by thermal denaturation experiments with synthetic double-stranded oligonucleotides, which contained one (TX) or no abasic site (TA). The acridizinium–adenine conjugates stabilize the DNA with the abasic position slightly more than they do the regular duplex, as indicated by the difference of the induced melting-temperature shifts between the TX and TA duplexes (ΔΔTm ≈ 4 °C) at a ligand/DNA ratio r of 0.5. Most notably, a significantly more efficient stabilization (ΔΔTm = 9.6 °C) of the abasic duplex is achieved by theaminoalkyl derivative, namely 9-{N-[3-(dimethylamino)propyl]carboxamido}acridizinium salt, which does not carry an adenine substituent. These results indicate that the design of abasic-site-targeting ligands must not necessarily involve the attachment of a nucleic acid base to the DNA intercalator.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

The cyclodehydration of bis(pyridiniummethyl)methylbenzenes 3a–b in polyphosphoric acid leads to methyl-substituted diazoniapentaphene salts 4a–b instead of linear diazoniapentacene derivatives, while the 1,3-bis(pyridiniummethyl)bromobenzene 3d forms a semi-betaine 4a,12a-diazoniapentaphen-14-olate 4d under these conditions. The mechanistic details of this rearrangement–cyclodehydration sequence may be explained by an intramolecular ipso-addition to the substituted benzene moiety, followed by an [1,2]-methyl shift in case of 4a–b or HBr elimination in case of 4d. The proposed mechanism was confirmed by the isolation of the intermediate hydroxy derivative 10b from the cyclization of 3a in refluxing HBr and conversion of 10b to the final product 4a by dehydration in polyphosphoric acid. Electronic absorption and fluorescence properties of the previously unknown diazoniapentaphene salts have been studied. Photophysical properties of 4a–b resemble the ones of the parent diazoniapentaphene salts, while semi-betaine 4d possesses a red-shifted absorption and fluorescence maxima, along with significant solvatochromism with respect to the absorption properties. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

The novel 2,6-donor–acceptor-substituted anthracene, namely 6-methoxy-2-anthracene carboxylic acid (7), was synthesized. The emission of this compound exhibits significant solvatochromism. The fluorescence band position and intensity are also remarkably sensitive to H+. Irradiation of the anthracene 7 in solution yields the syn and anti head-to-tail dimers exclusively. A synergistic electronic effect between the donor and acceptor substituents is proposed to operate on the photophysical and photochemical properties of anthracene 7.