Dehydro[12]- and [18]annulene-Fused Ball-Shaped Ruthenium Complex Oligomers: Synthesis, Aromatic/Antiaromatic Effect, and Symmetry for Near-Infrared Optical Properties.

The appropriate arrangement of near-infrared (NIR) chromophores allows for the modification of the peak wavelength in the NIR region and efficient use of NIR light. However, the preparation of novel NIR chromophores using simple procedures remains a formidable challenge. Herein, we report the synthesis of ball-shaped ruthenium complex oligomers. The metal complexes can be synthesized in a single step and interact strongly with NIR light. Alkyne-substituted low-symmetry ball-shaped ruthenium complexes were synthesized and subjected to Eglinton coupling to obtain dehydro[12] and [18]annulene-fused dimers and trimers. Fine-tuning of the reaction conditions led to the selective synthesis of the target oligomers. NMR spectroscopy confirmed that the 18π-aromatic and 12π-antiaromatic properties of the annulene influenced the ruthenium complex chromophore, and magnetic circular dichroism spectroscopy showed changes in the electronic structure of their excited state owing to molecular-symmetry differences. The absorption coefficient in the NIR region of the absorption spectra of the oligomers increased significantly, supporting the efficient use of light by oligomerization. The formation of oligomers using ball-shaped metal complexes is a simple and effective strategy for controlling NIR optical properties.

Direct Near Infrared Light-Activatable Phthalocyanine Catalysts.

The high penetration of near-infrared (NIR) light makes it effective for use in selective reactions under light-shielded conditions, such as in sealed reactors and deep tissues. Herein, we report the development of phthalocyanine catalysts directly activated by NIR light to transform small organic molecules. The desired photocatalytic properties were achieved in the phthalocyanines by introducing the appropriate peripheral substituents and central metal. These phthalocyanine photocatalysts promote cross-dehydrogenative-coupling (CDC) under irradiation with 810 nm NIR light. The choice of solvent is important, and a mixture of a reaction-accelerating (pyridine) and -decelerating (methanol) solvents was particularly effective. Moreover, we demonstrate photoreactions under visible-light-shielded conditions through the transmission of NIR light. A combined experimental and computational mechanistic analysis revealed that this NIR reaction does not involve a photoredox-type mechanism with electron transfer, but instead a singlet-oxygen-mediated mechanism with energy transfer.

Cationic Axial Ligand Effects on Sulfur-Substituted Subphthalocyanines.

Herein, we report the synthesis of sulfur-substituted boron(III) subphthalocyanines (SubPcs) with cationic axial ligands. Subphthalocyanines were synthesized by a condensation reaction using the corresponding phthalonitriles and boron trichloride as a template. An aminoalkyl group was introduced on the central boron atom; this process was followed by N-methylation to introduce a cationic axial ligand. The peripheral sulfur groups shifted the Q band of SubPcs to a longer wavelength. The cationic axial ligands increased the polarity and enhanced the hydrophilicity of SubPcs. The effect of axial ligands on absorption and fluorescence properties is generally small. However, a further red shift was observed by introducing cationic axial ligands into the sulfur-substituted SubPcs. This change is similar to that in sulfur-substituted silicon(IV) phthalocyanines. The unique effect of the cationic axial ligand was extensively investigated by theoretical calculations and electrochemistry. In particular, the precise oxidation potential was determined using ionization potential measurements. Thus, the results of the present study provide a novel strategy for developing functional dyes and pigments based on SubPcs.

Extremely Photostable Electron-Deficient Phthalocyanines that Generate High Levels of Singlet Oxygen.

A robust lead-mediated synthetic procedure for the generation of phthalocyanines substituted with electron-withdrawing groups has been developed. The free-base phthalocyanine and various metal complexes were prepared without discernible degradation of the peripheral electron-withdrawing substituents. Upon irradiation with red light, some of the thus-obtained metal complexes generated high levels of singlet oxygen. In particular, a palladium complex exhibited attractive photostability upon exposure to singlet oxygen as a bleaching agent. The photostability of such complexes that may manifest concomitantly to the generation of high levels of singlet oxygen was attributed to the presence of the electron-withdrawing groups, which results in energetically low-lying highest occupied molecular orbitals.

Chemoselective Synthesis of Aryloxy-Substituted Phthalocyanines.

The synthesis of the first examples of 8-fold α-aryloxy-substituted phthalocyanines is described. 3,6-Diiodophthalonitrile was used as a precursor for a series of 3,6-aryloxy-substituted phthalonitriles, and a lead-mediated macrocyclization was employed to afford the corresponding free-base phthalocyanine complexes. The optical, electrochemical, and aggregation properties of these complexes can be tuned by varying the substituents on the aryloxy groups or by changing the pH value.

(1,3)Pyrenophanes containing crown ether moieties as fluorescence sensors for metal and ammonium ions.

Crown ether containing (1,3)pyrenophanes 1-6 were synthesized, and UV absorption and fluorescence spectroscopic studies were carried out to determine their abilities to form complexes with metal and ammonium ions. The fluorescence spectra of 1.0 × 10-5 M solutions of 1, 2, 4 and 6 in 1 : 1 v/v CH2Cl2 : CH3CN were comprised of both monomer and intramolecular excimer emission bands, while only monomer emission bands were present in the fluorescence spectra of 3 and 5. The intensities of the intramolecular excimer emission bands of 1, 2, 4 and 6 in 1 : 1 v/v CH2Cl2 : CH3CN decreased and those of the monomer emission increased in conjunction with the existence of isoemissive points upon the addition of increasing concentrations of various metal perchlorates. The fluorescence spectral changes were dependent on the sizes of crown ether rings and metal ions and, as such, they reflected equilibrium constants for the formation of metal-crown ether complexes. Addition of n-Bu2NH2+PF6- or (PhCH2)2NH2+PF6- to the solutions of the (1,3)pyrenophane linked crown ethers, which brought about similar fluorescence spectral changes, led to the formation of pseudo-rotaxanes as was evidenced by an analysis of 1H NMR spectra and Job's plots. The fluorescence changes of 1 occurred during 5 cycles of repetitive addition and removal of Ba2+. The ratio of intensities of the monomer to the intramolecular excimer emission bands of 1, 2, 4 and 6 increased as the temperature decreased. Based on the experimental observations and the results of DFT calculations, it is concluded that the (1,3)pyrenophanes exist in solution as equilibrium mixtures of anti monomer emitting and syn intramolecular excimer emitting conformers and the equilibrium favors the anti form when the crown ether moieties form complexes with metal or ammonium ions.

Photoinduced three-component coupling reactions of electron deficient alkenes, dienes and active methylene compounds.

The irradiation of aqueous acetonitrile solutions, containing electron deficient alkenes, dienes and active methylene compounds along with sodium or cesium carbonate and catalytic amounts of phenanthrene or pyrene, gives rise to the formation of novel three-component coupling products and diene dimers. Cinnamonitrile and benzylidenemalononitrile and its derivatives serve as electron-acceptors; 2,5-dimethyl-2,4-hexadiene and malononitrile anion serve as electron donors in this process. Based on the results of UV-vis absorption spectroscopy and the calculated ΔG values for single electron transfer (SET), mechanisms are proposed for the coupling reaction involving photoinduced electron transfer (PET) between the electron deficient alkenes and dienes or malononitrile anion via direct excitation of electron deficient alkenes or redox photosensitization using phenanthrene or pyrene serving as a photosensitizer.

Effects of substituents in silyl groups on the absorption, fluorescence and structural properties of 1,3,6,8-tetrasilylpyrenes.

1,3,6,8-Tetrasilylpyrenes and related germyl and stannyl derivatives were synthesized, and their absorption and fluorescence spectroscopic and structural properties were elucidated. The results show that the UV-vis absorption maxima of these substances in CH2Cl2 solutions shift to longer wavelengths as the size of the alkyl groups and numbers of phenyl groups on silicon increase. Fluorescence quantum yields of tetrasilylpyrenes in cyclohexane are larger than that of pyrene, and a pentamethyldisilyl derivative has an emission efficiency of 0.79. Except in the case of the SiMe2H derivative, excimer emission was not observed in concentrated solutions of these substances. The SiMe2H and SiMe3 derivatives were shown to form CT complexes with tetracyanoethylene in CH2Cl2 solutions. The calculated energy barriers for rotation of the silyl groups about the Si-C bond increase as the steric bulk of the silyl group increases. 29Si NMR chemical shifts were found to depend on the sizes of the alkyl groups and numbers of phenyl groups. Data arising from theoretical calculations suggest that the silyl groups act as electron-donating groups, and the donating ability of the groups decreases in the order SiR3 > GeR3 > SnR3.

Synthesis and fluorescence properties of dioxa-, dithia-, and diselena-[3.3](1,3)pyrenophanes.

[3.3](1,3)Pyrenophanes tethered by oxygen (1), sulfur (2) and selenium (3) atoms were synthesized and the structural and physical properties of these substances were determined. The absorption maxima of the [3.3](1,3)pyrenophanes were observed to shift to longer wavelengths in the order of 1 < 2 < 3. The fluorescence spectra of 1-3 contained both monomer and intramolecular excimer emissions, which correspond to anti and syn conformers, respectively. The ratios of the intensities of intramolecular excimer to monomer emission were observed to increase with the increasing solvent polarity. The intensity ratios also depend on temperature. For example, an increase in temperature results in an increase of the ratio of intensities of the intramolecular excimer to monomer fluorescence of 2. The results of 1H NMR spectroscopic investigations show that resonances for the methylene and aromatic hydrogens in these substances coalesce at low temperatures with coalescence temperatures (Tc) that decrease in the order of 1 > 2 > 3. The results of geometry optimization studies using B3LYP/6-31G(d,p) demonstrate that the syn conformers of 1-3 have lower enthalpies than their anti counterparts, but the syn conformer of 1 and the anti conformers of 2-3 are entropically more favorable. These findings suggest that an equilibrium exists between the syn and anti conformers of the [3.3](1,3)pyrenophanes and that the conformer ratios are dependent on both the solvent polarity and temperature in a manner that can be explained in terms of a combination of enthalpies, dipole moments and entropies. The combined results show that the pyrenophanes are interesting substances that emit different fluorescence colors in a manner that is controlled by the surrounding environment.

Red-light-activatable ruthenium phthalocyanine catalysts.

Phthalocyanine ruthenium complexes were identified as red-light activatable catalysts for trifluoromethylation reactions. The red-light mediated chlorotrifluoromethylation of alkenes could proceed without any sacrificial reducing reagents. This reaction exhibited good compatibility with a blue-light-absorbing substrate, while under irradiation with blue light, i.e., under traditional photoreaction conditions, this substrate decomposed completely.

Temperature-dependent changes in the molecular orientation and visible color of phthalocyanine films.

A simple phthalocyanine zinc complex exhibits a visible color change in response to weak external stimuli, i.e., changes in solvent and temperature. Its chromism was attributed to its controlled aggregation via weak interactions between the central metal and peripheral oxygen atoms. In solution, intense absorption and fluorescence bands appeared in both the longer-wavelength and NIR region in non-coordinating solvents, while a simple sharp Q band was observed in coordinating solvents. Variable-temperature absorption spectra and fluorescence lifetime measurements were used to characterize the aggregation-induced absorption and emission in non-coordinating solvents. A selective aggregation-disaggregation process was also observed in thin films of this phthalocyanine zinc complex, and the optical properties of the film depend on the annealing temperature. The changes in the NIR region lead to a sizable visible color change that is recognizable by the naked human eye. The temperature-dependent control of the aggregation process in the thin film was confirmed using operando spectroscopy techniques.

One-step synthesis of ball-shaped metal complexes with a main absorption band in the near-IR region.

The design of near-IR materials is highly relevant to energy and pharmaceutical sciences due to the high proportion of near-IR irradiation in the solar spectrum and the high penetration of near-IR light in biological samples. Here, we show the one-step synthesis of hexacoordinated ruthenium and iron complexes that exhibit a main absorption band in the near-IR region. For that purpose, novel tridentate ligands were prepared by condensation of two diimines and four cyanoaryl derivatives in the presence of ruthenium and iron template ions. This method was applied to a wide variety of cyanoaryl, diimine, and metal ion combinations. The relationship between the structure and the optical and electrochemical properties in the resulting complexes was examined, and the results demonstrated that these compounds represent novel near-IR materials whose physical properties can be controlled based on rational design guidelines. The intense absorption bands in the 700-900 nm region were assigned to metal-to-ligand charge transfer (MLCT) transitions, which should allow applications in materials with triplet excited states under irradiation with near-IR light.

Ethynylpyrene Linked Benzocrown Ethers as Fluorescent Sensors for Metal Ions.

Substances containing ethynylpyrenes linked to either one or four benzocrown ethers were synthesized, and their absorption and fluorescence spectroscopic responses to metal ions were assessed. Addition of metal perchlorates to solutions of these substances promotes short wavelength shifts in their absorption and fluorescence maxima and increases in their fluorescence intensities. The magnitudes of the fluorescence intensity increases are dependent on the ring size and number of the crown ether and the nature of the metal cation. Association constants for complex formation were calculated using fluorescence intensity versus concentration data. Analysis using Job's plots showed that the substances containing one benzocrown ether moiety form 1:1 complexes with metal ions. Results of experiments employing repeated addition and removal of Mg(ClO4 )2 demonstrate that the ON-OFF fluorescence response can be repeated at least three times. Results of molecular orbital calculations show that complexation with metal ions lowers the energies of both the π and π* levels of the ethynylpyrene moiety and that in some cases the vacant orbital on the metal becomes the LUMO of the complex. An explanation of the spectroscopic changes promoted by metal ions is proposed in terms of electrostatic repulsion and structural regulation.

Cationic axial ligands on sulfur substituted silicon(iv) phthalocyanines: improved hydrophilicity and exceptionally red-shifted absorption into the NIR region.

Herein, we report the exceptionally red-shifted absorption of sulfur-substituted silicon(iv) phthalocyanines upon introduction of cationic axial ligands. The Q band was red-shifted to approximately 900 nm with improved hydrophilicity by the combination of peripheral sulfur substituents and axial ammonium ligands. One such phthalocyanine exhibited remarkable photocytotoxicity upon irradiation with NIR light (∼810 nm) in live cells.

Intramolecular Photoreactions of 9-Cyanophenanthrene-Linked Arylcyclopropanes.

With the aim of developing efficient and useful processes for the preparation of polycyclic organic compounds, intramolecular [3 + 2] photoreactions of 9-cyanophenanthrene-linked arylcyclopropanes were investigated. Photoreactions of 6a,b, which contain respective p-methoxyphenylcyclopropane and phenylcyclopropane moieties, form the intramolecular [3 + 2] photocycloadducts, endo- and exo-7a,b, along with the dihydroisochroman derivatives, cis- and trans-8a,b. The efficiency of the photoreaction of 6a is higher when benzene rather than acetonitrile is used as a solvent. Interestingly, this solvent effect is reversed in the photoreaction of 6b, where the efficiency is higher in acetonitrile than that in benzene. On the basis of the observed effects of substituents and solvents, fluorescence emission from intramolecular exciplexes, and ΔGs for intramolecular single electron transfer (SET), we propose that the photoreactions proceed through pathways involving the initial formation of singlet intramolecular exciplexes and/or SET between the excited 9-cyanophenanthrene and the ground-state arylcyclopropane moieties.

[4 + 2] Dimerization and Cycloaddition Reactions of alpha,beta-Unsaturated Selenoaldehydes and Selenoketones.

The reactions of alpha,beta-unsaturated aldehydes and ketones with bis(dimethylaluminum) selenide, (Me(2)Al)(2)Se, yield the corresponding alpha,beta-unsaturated selenoaldehydes and selenoketones. They are too unstable to be isolated in the monomeric form, but they undergo regioselective [4 + 2] dimerization via a "head-to-head" oriented transition state to afford diselenin derivatives (trans and cis isomers). Theoretical calculations at the density functional theory level show that this selectivity occurs because the "head-to-head" dimerization is thermodynamically favored over the "head-to-tail" by about 14 kcal/mol. Both dimerization reactions have low energy barriers: 1.5 and 2.8 kcal/mol for the former and 0.9 and 1.3 kcal/mol for the latter. In the presence of norbornadiene, these compounds function as 4pi heterodienes (C=C-C=Se) to give the respective cycloadduct products. On the other hand, they act as 2pi dienophiles (C=Se) in the reactions with cyclopentadiene except for selenoacrolein which serves as a 4pi diene and only one C=C bond (2pi) in cyclopentadiene is involved in the reaction. Theoretical calculations have been carried out in order to better understand these observations.