Naphthyl Chromophores Research Articles

Excited state properties of 2′-hydroxychalcone analogues functionalized with a diene moiety studied by steady state and laser flash photolysis

2′-Hydroxychalcone (HC) analogues 1 and 2 having a diene part tethering the phenyl and naphthyl chromophores, respectively, were prepared, and their photochemical and photophysical properties were studied. Fluorescence from these compounds was absent in solution and the solid state. Based on the results obtained upon steady state and laser flash photolyses, compound 2 was found to be substantially stable on photoirradiation without undergoing intersystem crossing to the triplet state whereas compounds 1 showed transient absorption due to the triplet tautomer. The deactivation processes in the excited states were discussed by considering energetic reaction diagrams for the corresponding tautomers and isomers.

Photoinduced energy- and electron-transfer from a photoactive coordination cage to bound guests.

In a coordination cage which contains an array of twelve naphthyl chromophores surrounding a central cavity, photoinduced energy or electron-transfer can occur from the chromophore array to the bound guest in supramolecular host/guest complexes.

Synthesis and photophysical and magnetic studies of ternary lanthanide(iii) complexes of naphthyl chromophore functionalized imidazo[4,5-f][1,10]phenanthroline and dibenzoylmethane.

The luminescent ternary lanthanide(iii) complexes [Ln(DBM)3(L1)] and [Ln(DBM)3(L2)] (Ln = Eu and Tb) of dibenzoylmethane (DBM) and 2-(2-naphthyl)-1H-imidazo[4,5-f][1,10]phenanthroline (L1) and 2-(2-hydroxy-1-naphthyl)-1H-imidazo[4,5-f][1,10]phenanthroline (L2) are reported in this work. The naphthyl chromophore functionalized imidazophenanthroline ligands L1 and L2 are structurally characterized by using single crystal X-ray diffraction: (L1), a = 14.933(4) Å, b = 7.4965(13) Å, c = 15.999(4) Å, α = γ = 90°, β = 102.670(7)°, V = 1747.4(6) Å3, Z = 4, monoclinic, P21/c and (L2), a = 7.8555(11) Å, b = 26.216(4) Å, c = 10.0748(17) Å, α = γ = 90°, β = 96.799(7)°, V = 2060.2(6) Å3, Z = 4, monoclinic, P21/n. A photophysical study reveals that the ligands L1 and L2 sensitize europium(iii) emission. The complexes [Eu(DBM)3(L1)] and [Eu(DBM)3(L2)] exhibit the characteristic emission of the Eu(iii) ion at 298 and 77 K. The terbium(iii) complexes [Tb(DBM)3(L1)] and [Tb(DBM)3(L2)] exhibit only ligand centred fluorescence at room temperature, while metal centred emission is observed at 77 K. The non-luminescence of the Tb(iii) center at room temperature is due to the proximity of the triplet states of the ligands to the 5D4 level of the Tb(iii) ion. DC magnetic susceptibility studies have been conducted on the Tb(iii) complexes in a 1 T field over the temperature range 20-300 K. The complexes display room temperature (300 K) χMT values of 9.69 and 10.21 cm3 mol-1 K, respectively. A gradual decrease in the χMT values is observed on reducing the temperature and reached the value of 7.80 and 6.60 cm3 mol-1 K, respectively, at 20 K. The decrease in the χMT values as the temperature is lowered could be attributed to the depopulation of the Zeeman split crystal field levels.

Structural and photophysical characterization of gold(I) complexes bearing naphthyl chromophores

We prepared two chlorido-gold(I) complexes of the type L–Au–Cl bearing a naphthyl moiety: Complex 1 with L=tris-1-naphthyl-phosphine shows standard linear coordination without further aggregation in the solid state. Complex 2 with L=2-naphthyl-isonitrile is engaged in a complex network of aurophilic and π–π interactions. The two complexes show similar luminescence behaviour in solution at room temperature with both intraligand fluorescence and phosphorescence. At 77K the emission spectra are dominated by intraligand phosphorescence, which is typical of gold complexes with extended π-chromophores.

Fibrils or Globules? Tuning the Morphology of Peptide Aggregates from Helical Building Blocks

The aggregation propensity of helical oligopeptides formed exclusively by the conformationally constrained α-aminoisobutyric acid (Aib or U in a three- or single-letter code, respectively) was studied in methanol and methanol/water solutions by spectroscopic methods (UV-vis absorption, steady-state and time-resolved fluorescence, and FT-IR absorption) and atomic force microscopy (AFM) imaging. The peptides investigated have the general formula UnN, where n = 6, 12, and 15 and N stands for a naphthyl chromophore introduced with the dual aim to serve as a spectroscopic probe and to analyze the effect of an extended aromatic group on the aggregation process. Experiments showed that the aggregation propensity in (70/30)v/v and (50/50)v/v methanol/water solutions increases with increasing the length of the peptide chain, i.e., U6N < U12N < U15N. When the peptides are immobilized on mica as a dried film, the interplay of aromatic-aromatic and interhelix interactions, the latter becoming more and more important with the elongation of the peptide chain, governs the morphology of the resulting mesoscopic aggregates. AFM imaging revealed the formation of globular or fibrillar structures, the predominance of which is controlled by the helix length of the peptide building block.

Syntheses, photophysical properties, and reactivities of novel bichromophoric Pd complexes composed of Ru(ii)–polypyridyl and naphthyl moieties

A series of novel bichromophoric Ru(II) complexes bearing a naphthyl chromophore linked with 2,2'-bipyridyl (bpy) and 2,2'-bipyrimidine (bpm) ligands were synthesized. Complexation with a Pd-alkyl unit led to the formation of bichromophoric Ru-Pd catalysts. The photochemical and electrochemical properties of the newly synthesized compounds were studied. It has been shown that the UV-light energy absorbed at the pendant naphthyl moiety is effectively transferred to the Ru(II) center; this is supported by the observation of metal-to-ligand charge-transfer luminescence through excitation of the naphthyl unit, which is identical to the luminescence observed through visible light excitation. The luminescence lifetime of the complex bearing a naphthyl moiety directly connected to the bpy ligands was lengthened to ca. 1000 ns. When a Pd complex containing the bichromophoric unit with an extended lifetime was used as a catalyst, styrene polymerization under visible or UV light irradiation was observed, in clear contrast to dimerization using other catalysts. These results indicate the formation of an excited-state with a prolonged excited-state lifetime, which promotes an insertion step in preference to the competing β-H elimination step.

Light‐Harvesting in Multichromophoric Rotaxanes

Two rotaxanes with benzyl ether axles and tetralactam wheels were synthesized through an anion template effect. They carry naphthalene chromophores attached to the stopper groups and a pyrene chromophore attached to the wheel. The difference between the two rotaxanes is represented by the connecting unit of the naphthyl chromophore to the rotaxane axle: a triazole or an alkynyl group. Both rotaxanes exhibit excellent light-harvesting properties: excitation of the naphthalene chromophores is followed by energy transfer to the pyrene unit with efficiency higher than 90% in both cases. This represents an example of light-harvesting function among chromophores belonging to mechanically interlocked components, that is, the axle and the wheel of the rotaxanes.

A molecular clip throws new light on the complexes formed by a family of cyclam-cored dendrimers with Zn(ii) ions. Efficient energy transfer in the heteroleptic complexes

Complexation of Zn(II) ions by cyclam cored dendrimers appended with four (G0), eight (G1) and 16 naphthyl chromophores (G2) at the periphery have been investigated in CH₃CN-CH₂Cl₂ 1 : 1 (v/v) solution by absorption and emission, ESI-mass and ¹H NMR spectroscopy. The results obtained can be interpreted by the formation of complexes of 2 : 1 dendrimer to metal stoichiometry, at low metal ion concentration, and 1 : 1 complexes upon further addition of Zn(II) ions, for all the dendrimer generations. Upon addition of a molecular clip C²⁻ consisting of two anthracene sidewalls bridged by a benzene group with two sulfate substituents in the para positions, heteroleptic complexes of general formula [GnZnC] are formed. Interestingly, in these complexes, a very efficient quenching (practically 100%) of the dendrimer naphthyl luminescence and sensitization (ca. 90%) of the clip anthracene emission take place. The complex [G2ZnC] exhibits a very high molar absorption coefficient in the UV spectral region owing to the 16 naphthyl chromophores of the dendrimer and the two anthracene units of the clip (ε = 1.7 × 10⁵ M⁻¹ cm⁻¹ at 263 nm). Furthermore, the excitation energy absorbed by the naphthyl chromophores is efficiently funneled to the two anthracene units of the clip, which emits in the blue spectral region.

Synthesis, Conformation and Chiroptical Properties of Diaryl Esters of Tartaric Acid

Previously unknown diaryl esters of l-tartaric acid have been synthesized. Their conformations have been studied by DFT calculations, NMR and circular dichroism spectroscopy in solution, as well as by X-ray diffraction in the crystalline state. The four-carbon tartrate chain of diaryl esters was found to be extended in all cases, with a higher degree of nonplanarity in the crystals. Dinaphthyl tartrates show unusually strong exciton Cotton effects (A = -228 for di-1-naphthyl l-tartrate) due to the coupling of allowed 1B(b) transitions in naphthyl chromophores, despite the acyclic structure and significant distance (over 10 A) between the two chromophores.

Intramolecular Exciplex Formation Induced by the Folding-Back Conformation of Poly(aryl ether) Dendrimers

A series of poly(aryl ether) dendrimers Gn-NA (n = 1−4), generations 1−4, containing a naphthyl core group were synthesized. The steady-state and time-resolved fluorescence studies reveal that Gn-NA (n = 1, 2) take a loose structure and Gn-NA (n = 3, 4) bear a more congested structure, which undergo the singlet electron transfer process in dichloromethane from dendritic backbone to the naphthyl group. As a consequence of the electron transfer process, an intramolecular exciplex is formed between the core naphthyl chromophore and the benzyloxy unit of dendritic backbone in G3-NA and G4-NA. Fluorescence measurements in the dichloromethane−acetonitrile binary solvents validate that the intramolecular exciplex formation can be enhanced by the folding back conformation of dendrimers.

Pure chiral organic thin films with high isotropic optical activity synthesized by UV pulsed laser deposition

We show that the pulsed laser deposition (PLD) technique allows us to elaborate pure molecular solid state thin films based on binaphthyl molecules featuring high isotropic optical rotation (HIOR). The transfer of chirality from the ablated target to the substrate was probed by polarimetry and circular dichroism (CD) measurements. A rotary power of 12° mm at 546 nm has been obtained. CD spectroscopy confirms both the chiral and the isotropical nature of the deposited thin films and put into evidence the disorder between the naphthyl chromophores inside the molecular material. Finally, we highlight three regimes for the deposition mechanism depending on the laser fluence: desorption without racemisation, desorption with racemisation, and ablation with degradation. These results demonstrate that, by properly adjusting the growth conditions, isotropic purely organic chiral films can be grown by PLD, thereby opening the prospect for the synthesis of high value organic materials for applications such as waveguiding.

Photoactive Modified Chitosan

A water-soluble polymeric photosensitizer that contains naphthyl chromophores and absorbs light in the near UV region was obtained by modification of chitosan. The excitation energy can be used to induce photochemical reactions via energy and electron transfer.

Photo‐Fries Rearrangement in Polymeric Media: An Investigation on Fully Aromatic Esters Containing the Naphthyl Chromophore

AbstractThe present paper deals with the photo‐Fries rearrangement of fully aromatic esters in polymeric media. Low molecular weight aryl esters bearing the 1‐naphthyl chromophore were investigated with respect to their photochemical reactivity and the yield of hydroxyketones as the photo‐Fries rearrangement product. In particular, the phenyl, 4‐methylphenyl and 1‐naphthyl ester of 1‐naphthoic acid, as well as benzoic acid, 1‐naphthyl ester were dissolved in a polysiloxane matrix and exposed to 313 nm UV light. The progress of the photoreaction was assessed by quantitative FT‐IR spectroscopy. Both 1‐naphthoic acid, phenyl ester and benzoic acid, 1‐naphthyl ester underwent the photoreaction upon 313 nm irradiation. This indicates that in these fully aromatic esters, the initial CO bond scission also occurs upon selective photoexcitation of the acyl unit in the molecule. It was found that phenyl and 4‐methylphenyl esters of 1‐naphthoic acid gave the highest yields of hydroxyketone when irradiated in polymer matrix. Based upon these results, a photoreactive monomer was designed which contains naphthoic acid, phenyl ester units attached to a norbornene ring. This monomer was then polymerized by ring opening metathesis polymerization (ROMP). The polymer showed a high yield in the photo‐Fries reaction upon 313 nm illumination. Moreover, a large increase in the refractive index (Δn up to +0.043 at λ = 370 nm) was observed which makes this polymer interesting for optical applications (e.g., waveguiding and diffractive optics).magnified image

A fluorescent guest encapsulated by a photoreactive azobenzene dendrimer

We have studied the adduct formed by N,N′-2,7-didecyldiazapyrenium (P2+), as the hexafluorophosphate salt, with a third generation dendrimer (D) that comprises 14 tertiary amine units in the interior, and 16 naphthyl and 16 trans-azobenzene units in the periphery. A strong charge-transfer interaction between the electron-accepting diazapyrenium dication and electron-donating amine units of the dendrimer interior leads to a host–guest complex with 1 : 1 stoichiometry, namely D(16t)⊃P2+. The self-assembly process can be easily monitored by strong changes in the absorption and emission spectra: (i) new absorption bands (λmax ≈ 445 and 565 nm) at lower energy compared to the isolated species arise, (ii) a strong quenching of the intense diazapyrenium fluorescence is observed, and (iii) a new broad emission band, typical of the charge-transfer complex, appears with a maximum at 660 nm at 298 K and 600 nm at 77 K. By global analysis of the absorption spectra, an association constant of 1.0 × 106 M−1 is obtained for D(16t)⊃P2+, compared to 3.0 × 104 M−1 in the case of the adduct of P2+ with triethylamine under the same experimental conditions. This result demonstrates that the presence of bulky substituents at the dendrimer periphery does not hinder the formation of a stable complex and suggests a cooperative effect due to the multiple amine groups of the dendrimer branching points. No energy transfer from the azobenzene or naphthyl chromophores to the charge-transfer complex has been evidenced. The self-assembly process can be reversed upon addition of an equimolar amount of trifluoromethanesulfonic acid. An adduct with 1 : 1 stoichiometry is formed also between P2+ and D(2t14c), a species obtained from D(16t) upon irradiation at 365 nm: the corresponding association constant is very similar to that of D(16t)⊃P2+, showing that the isomeric state of the peripheral azobenzene units does not affect the stability of the adduct.

Ultrasound induced formation of organogel from a glutamic dendron

New l-glutamic acid based dendritic compounds: N-(2-naphthacarbonyl)- l-glutamic acid diethyl ester (NGE) and N-(2-naphthacarbonyl)-1,5-bis( l-glutamic acid diethyl ester)- l-glutamic diamide (NBGE) were designed. Although NGE could not form any gels in common solvents, NBGE could form stable gels in hexane, toluene, and water under ultrasound. Three dimensional network structures composed of fibers with various diameters were observed in the gel by SEM and TEM. FTIR spectral measurement revealed that ultrasound during cooling of the solution could destroy some of the hydrogen bond interactions and caused the gel formation. In solution, no CD signal was detected because the naphthyl chromophore is far from the chiral center. In the gel, however, CD signals assigned to the naphthyl group were observed, which indicated that the chirality of the chiral center could be transferred to the chromophore in the supramolecular organogel system.

Synthesis and Structural and Photoswitchable Properties of Novel Chiral Host Molecules: Axis Chiral 2,2‘-Dihydroxy-1,1‘-binaphthyl-Appended stiff-Stilbene1

Novel photoswitchable chiral hosts having an axis chiral 2,2'-dihydroxy-1,1'-binaphthyl (BINOL)-appended stiff-stilbene, trans-(R,R)- and -(S,S)-1, were synthesized by palladium-catalyzed Suzuki-Miyaura coupling and low-valence titanium-catalyzed McMurry coupling as key steps, and they were fully characterized by various NMR spectral techniques. The enantiomers of trans-1 showed almost complete mirror images in the CD spectra, where two split Cotton effects (exciton coupling) were observed in the beta-transitions of the naphthyl chromophore at 222 and 235 nm, but no Cotton effect was observed in the stiff-stilbene chromophore at 365 nm. The structures of (R)-10 and trans-(R,R)-1 were confirmed by X-ray structural analysis. The optimized structure of cis-1 by MO calculations has a wide chiral cavity of 7-8 A in diameter, whereas trans-1 cannot form an intramolecular cavity based on the X-ray data. Irradiation of (R,R)-trans-1 with black light (lambda = 365 nm) in CH3CN or benzene at 23 degrees C led to the conversion to the corresponding cis-isomer, as was monitored by 1H NMR, UV-vis, and CD spectra. At the photostationary state, the cis-1/trans-1 ratio was 86/14 in benzene or 75/25 in CH3CN. On the other hand, irradiation of the cis-1/trans-1 (75/25) mixture in CH3CN with an ultra-high-pressure Hg lamp at 23 degrees C (lambda = 410 nm) led to the photostationary state, where the cis-1/trans-1 ratio was estimated to be 9/91 on the basis of the 1H NMR spectra. The cis-trans and trans-cis interconversions could be repeated 10 times without decomposition of the C=C double bond. Thus, a new type of photoswitchable molecule has been developed, and trans-1 and cis-1 were quite durable under irradiation conditions. The guest binding properties of the BINOL moieties of trans- and cis-(R,R)-1 with F-, Cl-, and H2PO4- were examined by 1H NMR titration in CDCl3. Similar interaction with F- and Cl- was observed in trans-1 (host/guest = 1/1, Kassoc = (1.0 +/- 0.13) x 103 for F- and (4.6 +/- 0.72) x 102 M-1 for Cl-) and cis-1 (host/guest = 1/1, Kassoc = (1.0 +/- 0.13) x 103 for F- and (5.9 +/- 0.69) x 10 M-1 for Cl-), but H2PO4- interacted differently: the cis-isomer formed the 1/1 complex (Kassoc = (9.38 +/- 2.67) x 10 M-1), whereas multistep equilibrium was expected for the trans-isomer.

Removal of Pentachlorophenol from Water Using Novel Smart Hydrogel Microspheres

AbstractThe thermoresponsive hydrogel microspheres were obtained by copolymerization of N-isopropylacrylamide (NIPAM) and 2-hydroxyethyl methacrylate (HEMA) crosslinked with N,N’-methylenebisacrylamide (BIS). The hydrogel was then functionalized using 1-naphthyl glycidyl ether (NGE) to attach naphthyl chromophores, which absorb UV light and act as photosensitizers. The ability of the functionalized microspheres to photosensitize dechlorination reactions was confirmed using pentachlorophenol (PCP) as a model compound.

Ultrafast Decarboxylation of Carbonyloxy Radicals: Influence of Molecular Structure

Experimental and theoretical investigations on the ultrafast photoinduced decomposition of three tert-butyl peroxides of general structure R−C(O)O−O−tert-butyl with R = phenyloxy, benzyl, or naphthyloxy in solution are presented. Photoinduced O−O bond scission occurs within the time resolution (200 fs) of the pump−probe experiment. The subsequent dissociation of photochemically excited carbonyloxy radicals, R−CO2, has been monitored on a picosecond time scale by transient absorption at wavelengths between 290 and 1000 nm. The measured decay of R−CO2 is simulated via statistical unimolecular rate theory using molecular energies, geometries, and vibrational frequencies obtained from density functional theory (DFT) calculations. The results are compared with recent data for tert-butyl peroxybenzoate (R = phenyl). While benzoyloxy radicals exhibit nanosecond to microsecond lifetimes at ambient temperature, insertion of an oxygen atom or a methylene group between the phenyl or naphthyl chromophore and the CO2 ...

Excited state properties of Ir III(phpy) 2(naphthylalaninate) with phpyH = 2-phenylpyridine : Energy transfer and luminescence

The complex Ir III(phpy) 2(nala) with phpyH = 2-phenylpyridine and nalaH = 3-(2-naphthyl)alanine was prepared and characterized. The electronic spectrum of the complex shows long-wavelength absorptions which are attributed to the Ir III(phpy) 2 chromophore. The lowest-energy excited state is a metal-to-ligand charge transfer (MLCT) triplet which is emissive under ambient conditions. Excitation of the naphthyl chromophore at shorter wavelength is followed by an efficient energy transfer to the Ir III(phpy) 2 fragment.

Synthesis, stereochemistry and chiroptical properties of naphthylphenyl-substituted optically active oligosilanes with α,ω-chiral silicon centers

Novel naphthylphenyl-substituted optically active oligosilanes with α,ω-chiral silicon centers were synthesized. The absolute configuration of (1 R,2 R)-1,2-dimethyl-1,2-di(1-naphthyl)-1,2-diphenyldisilane ( R, R)- 3, one of the oligosilanes, was determined by X-ray diffraction, which gave a direct evidence for the retention and inversion stereochemistry of attacking silylanion and attacked chlorosilane. The intense π–π interaction of aryl substituents on chiral silicon centers enhanced by σ–π conjugation with oligosilane unit made it possible to clearly assign the absolute configuration and stable conformation of the optically active oligosilanes. The disilane ( R, R)- 3 showed positive exciton chirality originated from π–π interactions of 1B b,Np transition bands of two naphthyl chromophores on the adjacent silicon atoms. Contrary to this, (1 R,3 R)-1,3-di(1-naphthyl)-1,3-diphenyl-2-trimethylsilyl-1,2,3-trimethyltrisilane ( R, R)- 5, having silylene spacer with bulky trimethylsilyl group as branched substituent between two chiral centers, showed positive exciton chirality by interaction between red-shifted 1L a,Ph and 1B b,Np on the same silicon atom. (1 R,3 R)-1,3-Di(1-naphthyl)-1,3-diphenyl-1,2,2,3-tetramethyltrisilane ( R, R)- 4, which has dimethylsilylene group between two chiral silicon centers, showed two exciton chiralities, namely, positive chirality by 1L a,Ph and 1B b,Np on the same silicon atom, and negative chirality by two 1B b,Np on the adjacent silicon atoms. The intensified negative Cotton effect at 234 nm was caused by overlapping of Cotton effects of two exciton chiralities.