Naphthalene Chromophores Research Articles

The Synthesis of Rigid Chromophore–Spacer–Chromophore Dyads and Three-Armed Triads by the 1,3-Dipolar Reaction of Cyclobutene Epoxides with Aromatic Dipolarophiles

A series of polyaromatic hydrocarbons (PAHs) or their aza derivatives were reacted as dipolarophiles with ring-fused cyclobutene epoxides (CEs) in the 1,3-dipolar cycloaddition protocol to form 1:1 cycloadducts. The dihydroforms of the PAH chromophores contained in the rigid alicyclic scaffold were dehydrogenated to regenerate the original PAH chromophore and constituted a new route to rigid chromophore-nσ-PAH dyads separated by an alicyclic scaffold. The anthracene 1:1 adduct derived from the reaction with the 5,8-dimethoxynaphthalene-containing CE was reacted a second time to produce stereoisomeric three-armed triads in which naphthalene chromophores were attached rigidly onto scaffold. Two approaches were used to generate the incipient cyclic 1,3-dipolar intermediates involved in cycloaddition process. The first method employed ring-opening of functionalised CEs, the other method produced the dipolar reagent in situ by loss of dinitrogen from the initially formed adduct resulting from treatment of fused norbornenes with 2,5-bis(trifluoromethyl)-1,3,4-oxadiazole.

Hexahelicenophanes

AbstractA reaction sequence was studied for the preparation of cyclophanes 12, which contain 2,7‐bis(2‐phenylethenyl)naphthalene chromophores and polymethylenedioxy chains of different length. The irradiation of 12 in the presence of I2 led then, by oxidative cyclization processes, to the hexahelicenophanes 13, provided that the methylenedioxy chain of 12 is long enough (n = 8, 10). As competitive photoreaction, a twofold [2π+2π] cyclodimerization occurred, which furnished the belt cyclophanes 14. The latter process is the only photoreaction for 12 with n=6. The hexahelicenophanes 13 have lower racemization barriers and longer spinlattice relaxation times compared to those of hexahelicenes.

Influence of Drug Encapsulation within Mixed Micelles on the Excited State Dynamics and Accessibility to Ionic Quenchers

Photophysical techniques, specifically time-resolved fluorescence and laser flash photolysis, have proven to be noninvasive, straightforward, and valuable tools to demonstrate how drug encapsulation into biomimetic mixed micelles (MM) influences the dynamics of excited states and their accessibility to ionic quenchers. This concept has been illustrated by choosing a set of currently administered drugs containing a common naphthalene chromophore, namely, (S)-naproxen and its methyl ester, (R)-cinacalcet and (S)-propranolol. A remarkable increase of their triplet lifetimes is noticed when experiments are performed in MM, indicating efficient entrapment of the drugs in these supramolecular entities. Furthermore, a decrease of 1 order of magnitude in the quenching rate constant of the singlet and triplet excited states (by iodide or nitrite, respectively) is observed upon encapsulation into MM. This approach can in principle be extended to other microenvironments capable of incorporating photoactive compounds.

The first substituted macrocyclic ligand Py2N4S2 containing four naphthylmethylene pendant-armed groups: Synthesis and photophysical properties

Abstract The synthesis of a pendant donor emissive macrocyclic ligand Py2N4S2 with up to four naphthylmethylene arms (L) has been achieved. Their derivative solid metal complexes (Co2 +, Ni2 +, Cu2 +, Zn2 +, Cd2 +, Hg2 + and Ag+) have been isolated and characterized. The photophysical properties of the free ligand L and their complexation behaviour have been investigated in solution. In dichloromethane, the free ligand presents two emission bands which are related to the monomer naphthalene emission and a red-shifted band attributable to ground state dimers (interaction between two naphthalene chromophores), which was further validated from time-resolved data, with bi-exponential decay with absence of dynamic components. UV–Vis spectroscopy has revealed a 2:1 binding stoichiometry for Co2 +, Cu2 +, Zn2 +, Hg2 + and Ag+.

Nitroxide-mediated Polymerization of 2-(4-vinyl-benzyloxy)-naphthalene

Initiated by tetraethylthiuram disulfide, the solution polymerization of a new monomer, 2-(4-vinyl-benzyloxy)-naphthalene (VBN), which had naphthalene chromophore was successfully conducted in the presence of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO). While using benzoyl peroxide as initiator, the polymerization was out of control under equal conditions. The poly(2-(4-vinl-benzyloxy)-naphthalene) (PVBN) and copolymer of VBN and styrene (poly(VBN-co-St)) had strong fluorescence emission at 350 nm, excited at 274 nm. Although the polystyrene (PS) had no fluorescence emission excited at 274 nm, the fluorescence intensities of poly(VBN-co-St) were enhanced with the increase of styrene feed ratio.

FRET-based ratiometric fluorescent probes for selective Fe3+ sensing and their applications in mitochondria

Efficient ratiometric fluorescent Fe(3+) probes were designed and synthesized by linking a conjugated naphthalene chromophore to a rhodamine platform and a lipophilic triphenylphosphonium (TPP) cation. The probes could sensitively and selectively detect mitochondrial Fe(3+) in living cells.

The electronic structure of pyracene: a spectroscopic and computational study

We report a synthetic, spectroscopic and computational study of the polycyclic aromatic molecule pyracene, which contains aliphatic five-membered rings annealed to a naphthalene chromophore. An improved route to synthesize the compound is described. Gas-phase IR and solid-state Raman spectra agree with a ground-state D2h structure. The electronically excited S1 A(1)B3u state has been studied by resonance-enhanced multiphoton ionisation. An adiabatic excitation energy T0 = 30,798 cm(-1) (3.818 eV) was determined. SCS-ADC(2) calculations found a D2h minimum energy structure of the S1 state and yielded an excitation energy of +3.98 eV, including correction for zero point vibrational energy. The spectrum shows a rich low-frequency vibrational structure that can be assigned to the overtones of out-of-plane deformation modes of the five-membered rings by comparison with computations. The appearance of these modes as well as the frequency reduction in the excited state indicate that the potential in the S1 state is very flat. At higher excess energies most bands can be assigned to fundamentals, overtones and combination bands of either totally symmetric ag modes or of b2g modes that appear due to vibronic coupling. Lifetimes between 43 ns and 76 ns were measured for a number of vibronic bands. For the S2 state an equilibrium geometry with a non-planar carbon framework was computed. In addition a signal from the pyracene dimer was present. The spectrum shows several broad and structureless transitions. The origin band has a maximum at around 329 nm (30,400 cm(-1)). Again lifetimes between 60 ns and 70 ns were found. The dimer ion signal rises within less than 10 ps. Computations show that a crossed geometry with the long axis of one unit aligned with the short axis of the second constitutes the most stable structure. The broadening of the bands is most likely caused by excimer formation.

Cyclic Side‐Chain Phenylazo Naphthalene Polymers: Enhanced Fluorescence Emission and Surface Relief Grating Formation

Well-defined cyclic-polymers (cyclic-PAzoMMAs), bearing side-chain phenylazo naphthalene chromophore, were successfully synthesized by the combination of atom transfer radical polymerization (ATRP) and copper(I)-catalyzed azide/alkyne cycloaddition "click" reaction, as verified by GPC, (1) H NMR, FTIR, and MALDI-TOF mass spectrometry. The cyclic-PAzoMMA showed higher glass transition temperatures than the linear-PAzoMMA with the same molecular weight. Interestingly, the cyclic-PAzoMMA exhibited deeper modulation depth (M.D.) induced by SRG, larger value of the photoinduced birefringence, increased fluorescence emission, and longer fluorescence lifetime in comparison with its linear counterpart.

Self‐Organization of Hydrogen‐Bonding Naphthalene Chromophores into J‐type Nanorings and H‐type Nanorods: Impact of Regioisomerism

Regioisomere selbstorganisierende Moleküle bilden unterschiedliche null- und eindimensionale Nanostrukturen: Nanoringe bzw. Nanostäbe (siehe Bild) mit excitonischer Kopplung der Naphthalinchromophore vom J- bzw. H-Typ. In den flüssigkristallinen Zuständen liegen H-Brücken-gebundene Rosetten vor, was erklärt, wie die beobachteten Regioisomere zu unterschiedlichen Nanostrukturen mit charakteristischen excitonischen Wechselwirkungen führen. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Self‐Organization of Hydrogen‐Bonding Naphthalene Chromophores into J‐type Nanorings and H‐type Nanorods: Impact of Regioisomerism

Self‐Organization of Hydrogen‐Bonding Naphthalene Chromophores into J‐type Nanorings and H‐type Nanorods: Impact of Regioisomerism

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.

Self-association of a naphthalene-capped-β-cyclodextrin through cooperative strong hydrophobic interactions

NMR, circular dichroism and fluorescence techniques were used to study the structure in solution of a new β-cyclodextrin derivate in which naphthalene chromophore group is bridged to O(2) and O(3) secondary positions of the same glucopyranose unit through a bidentate hinge. The results point to the formation of a very stable dimer in aqueous solution which dissociates in non-polar solvents. Dimerization was enthalpy and entropy favoured. The hydrophobic character of the naphthyl moiety plays a very important role in the entropy change sign. Molecular mechanics as well as molecular dynamics calculations indicated that the most stable dimers are head-to-head oriented. For these dimer structures the naphthyl moieties, relatively shielded from the solvent, are sufficiently close to each other to couple their transition moments, but without forming excimers.

Spectroscopic and Molecular Modeling Studies of the Inclusion Complex of TNBAB with β-cyclodextrin in Aqueous Solution

Abstract In this investigation, a novel surfactant (N, N, N-trimethyl-4-(5-(octyloxy) naphthalene-1-yloxy) butan-1-aminium bromide, TNBAB) with a naphthalene chromophore moiety was designed and synthesized. The UV, fluorescence and 1H NMR measurements and molecular modeling have been carried out at 298.2 K for TNBAB + H2O, and TNBAB + β-CD + H2O systems. The stoichoimetry, stability constant and potential energy surface for the inclusion complex of TNBAB and β-CD have been determined. The results of UV and fluorescence suggested that β-CD formed strong complex with TNBAB, the stoichoimetry was found to be almost 1:1, and the inclusion constants obtained are larger than 2.1×104 L mol-1. 1H NMR and molecular modeling studies indicated β-CD and TNBAB could form a two different inclusion complexes (Fig. 9), the two part of the aliphatic chain (one including partly naphthalene nucleus) were encapsulated in the cavity of the β-CD through hydrophobic interaction, respectively.

Energy Transfer in Single-Stranded DNA-Templated Stacks of Naphthalene Chromophores

We have investigated energy transfer in a novel self-assembled DNA hybrid structure composed of diaminopurine-equipped naphthalene derivatives that are hydrogen-bonded along a single-stranded oligothymine template. By performing time-resolved measurements of the naphthalene donor luminescence decay in the absence and presence of a cyanine Cy3.5 acceptor bonded covalently to the 5′ end of the oligothymine, we have examined the role of temperature and DNA template length on energy transfer from donors to the acceptor. We find that energy transfer rates decline with increasing temperature over a fairly narrow (±5 °C) range over which changes in circular dichroism and donor luminescence lifetime indicate that the chiral assemblies are dissociating. In addition, the transfer rates exhibit a complex dependence on template length, increasing from initially low values for 10 bases toward an optimum for 30 bases and then declining again toward 60 bases. We find that for short (∼10 bases) templates, incomplete fill...

Phosphate selective alkylenebisurea receptors: structure-binding relationship

New host molecules for anions, adamantane, and alkyl urea derivatives substituted by naphthalene chromophores, were synthesized. Their binding with F −, Cl −, Br −, OAc −, HSO 4 −, NO 3 −, and H 2PO 4 − was investigated by UV–vis, fluorescence and NMR spectroscopy. The anion binding ability of adamantyl bisurea derivatives was compared with the analogous host molecules, wherein the urea moieties are separated by flexible alkyl linkers of the same length, and adamantane monourea derivative. The host molecules show the highest selectivity toward F − and H 2PO 4 −. The binding stoichiometry and the values of the association constants depend on the basicity of anions, availability of H-bonding sites, preorganization, and rigidity of the hosts, as well as solvent polarity and H-bonding availability. Rigid adamantane receptors, compared to flexible analogues show increased selectivity for H 2PO 4 −, whereas binding of OAc − is better with flexible receptors. The binding of OAc − and H 2PO 4 − was investigated by microcalorimetry. The stoichiometries and the stability constants of the corresponding complexes obtained by this method were in good agreement compared to those determined by UV–vis titrations. In both cases the enthalpic contribution to the overall complex stability was predominant.

Naphthalene Triplet Excited State as a Probe for the Assessment of Drug Distribution in Binary Protein Systems

Three drugs containing the naphthalene (NP) chromophore, namely, naproxen (NPX), propranolol (PPN), and cinacalcet (CIN), but with different affinities toward serum albumins (SAs) and α-1-acid glycoproteins (AAGs) have been employed for the assessment of drug distribution in binary SA/AAG systems. These three drugs represent an appropriate choice for checking whether a methodology based on transient absorption spectroscopy of a given reporter can be employed for discrimination between different distribution patterns in multicompartmental biological media. Thus, upon laser flash photolysis (LFP) of NPX, PPN, and CIN in the presence or absence of proteins, the NP triplet excited state ((3)NP*) at ∼420 nm was always detected, although the kinetics of the decay traces was structure- and medium-dependent. In aerated PBS, only a very short triplet lifetime (τ(T)) was found (1-2 μs). By contrast, in the presence of SAs, two longer triplet lifetimes (5-76 μs) were observed, ascribed to (3)NP* within site I and site II. Upon binding to AAGs, only a long τ(T) (15-47 μs) was found. When the two proteins were present simultaneously in the same media, fitting of the decay traces was clearly consistent with a distribution of the drug between the different biological compartments and the bulk solution, which correlates well with the known protein affinities of every drug. Experiments were performed in both human (HSA/HAAG) and bovine protein media (BSA/BAAG). The results showed that SAs are the major carriers for NPX; by contrast, PPN binds preferentially to AAGs. An intermediate situation was found for CIN, which presents comparable affinity for both proteins. The results obtained for the two enantiomers of each drug were very similar, although a small stereodifferentiation was observed between the triplet lifetimes in the protein binding sites.

Enhanced Photosafety of Cinacalcet upon Complexation with Serum Albumin

Cinacalcet (CIN) is a calcimimetic drug, which contains a naphthalene chromophore and binds almost quantitatively to human serum albumin (HSA). In the present work, the excited states of CIN have been characterized in order to obtain relevant information about complexation of CIN with HSA. The fluorescence spectrum in acetonitrile, at λ(exc) = 290 nm, displayed two bands with maxima at 332 and 439 nm, assigned to the monomer and exciplex emission. Upon protonation of the amino group, the exciplex band disappeared, with a concomitant increase of the monomer emission intensity. Time-resolved fluorescence evidenced an intramolecular dynamic quenching, attributed to exciplex formation and/or photoinduced electron transfer, in agreement with the favorable thermodynamics predicted by the Rehm-Weller equations. Diffusion controlled dynamic quenching of CINH(+) fluorescence by oxygen was observed. The emission properties in PBS were similar to those obtained for CINH(+) in acetonitrile. Laser flash photolysis (LFP) of CIN and CINH(+) in acetonitrile/N(2), at λ(exc) = 308 nm, gave rise to the naphthalene-like triplet excited states, with maxima at 420 nm and lifetimes of 4 and 7 μs; they were efficiently quenched by oxygen. No significant singlet excited state interaction was observed in CINH(+)/HSA complexes, as revealed by the emission spectra, which were roughly explained taking into account the relative contributions of drug and protein in the absorption spectra. Upon LFP of the complexes, triplet excited states were generated; the decays monitored at 420 nm were satisfactorily fitted using a function containing two monoexponential terms, corresponding to a short-lived (τ(1) = 8 μs) and a long-lived (τ(2) = 37 μs) component. This indicates that the drug is incorporated into two different binding sites of HSA. Despite the long triplet lifetimes of the CINH(+)/HSA complexes, the rate constant of quenching by oxygen was found to be 2 orders of magnitude lower than that determined in acetonitrile, which can be attributed to the relative slower diffusion rates in this microheterogeneous system. Therefore, the protein microenvironment protects cinacalcet from attack by oxygen; this prevents the phototoxic effects caused by formation of singlet oxygen and results in an enhanced photosafety of the drug.

Monolayers and Langmuir–Blodgett films of luminescent 1,3,5-triazine derivatives containing naphthalene or anthracene chromophores

Monolayer behaviors and Langmuir–Blodgett (LB) films of three luminescent aryl triazines, 2,4,6-tri(naphthalen-1-yl)-1,3,5-triazine (TN 1Ta), 2,4,6-tri(naphthalen-2-yl)-1,3,5-triazine (TN 2Ta), and 2,4,6-tri(anthracen-9-yl)-1,3,5-triazine (TATa) have been investigated. Surface pressure-area isotherms indicated that pure aryl triazines were difficult to form stable monolayers, while their mixtures with arachidic acid (AA) could be stabilized at the air–water interface. The mixed LB films of triazine-AA were deposited on substrate surfaces and analyzed by using UV–vis and infrared absorption spectra, X-ray photoelectron spectra, as well as scanning electron microscopy. Morphologies of the LB films and molecular aggregates were closely dependent on the structure of triazines and the surface pressures of deposition. Under UV radiation, TN 1Ta and TN 2Ta emitted at 410–460 nm while TATa emitted at 500–510 nm, with the emission lifetime falling into the range of 0.29 to 10.8 ns. Compared with those in solutions, the emissions of aryl triazines were red shifted in the LB films, especially for the TN 1Ta-AA and TN 2Ta-AA, which was attributed to the closely packed arrangement for the molecules in the LB films.

Pressure dependence of phosphorescence through energy transfer from inorganic quantum well to naphthalene chromophore in (C10H7C2H4NH3)2PbCl4

The organic-inorganic hybrid quantum well compound, (C10H7C2H4NH3)2PbCl4, exhibits enhanced phosphorescence due to the energy transfer from the excitonic state of inorganic quantum well to the triplet state of naphthalene chromophore. In the present study, photoluminescence and optical absorption spectra of (C10H7C2H4NH3)2PbCl4 were investigated under pressure to 6.5 GPa in order to investigate the pressure dependence of the energy transfer. The phosphorescence intensity decreases with pressure up to 5 GPa, while the energy of the triplet state of naphthalene chromophore does not change with pressure. From the absorption spectra under pressure, it is found that the exciton energy of inorganic quantum well decreases with pressure up to 5 GPa. In our experiment, the energy transfer from the singlet state of naphthalene chromophore exited by ultraviolet light at 3.82 eV to the singlet exciton of inorganic quantum well occurs, and then the singlet exciton is converted to the triplet exciton by intersystem crossing, which is followed by the energy transfer to the triplet state of naphthalene chromophore for phosphorescence. Our observations on phosphorescence can be explained by a change in the energy difference between the excitonic state of inorganic quantum well and the singlet state of naphthalene chromophore with pressure.

Synthesis, structure and luminescence of 1,8-diaurionaphthalenes

Reaction of 1,8-dilithionaphthalene with [AuCl(Et3P)] or [Au2Cl2(μ-dppm)] (dppm = bis(diphenylphosphinomethane)) in Et2O/THF leads to formation of bis(triethylphosphine)-1,8-diaurionaphthalene (1) and dppm-1,8-diaurionaphthalene (2), respectively. The dppm ligand present in complex 2 bridges the two gold centers leading to formation of short intramolecular Au–Au distances of av. 2.85 Å. Complex 2 reacts with AgPF6 in THF/CH2Cl2 to afford a dicationic Au4Ag2 complex which has been isolated as the bis(hexafluorophosphate) salt (3). In this cluster, two molecules of 2 sandwich two Ag cations resulting in the formation of a Au2AgAu2Ag six-membered ring in which the metal centers are connected by Au–Au (av. 2.84 Å) and Au–Ag (av. 2.75 Å) metallophilic interactions. This cluster is further stabilized by short Ag–C interactions involving some of the naphthalene carbon atoms. The luminescence spectra of 2 and 3 have been recorded. Both complexes display relatively broad emission bands centered at 540 nm which result, at least in part, from the heavy atom induced phosphorescence of the naphthalene chromophore.