Synthesis and photophysics of acridine derivatives

Highly fluorescent acridine derivatives were prepared by a multistep synthesis starting from 2-chlorobenzoic acid and the approapriate (aminophenyl)alkanoic acid by means of a modified Ullmann-Jourdan reaction followed by a cyclodehydration step, and by amination in the case of aminoacridine analogues. The obtained derivatives were subjected to photophysical studies (absorption and fluorescence). The compounds displayed interesting absorption behavior and high quantum yield of fluorescence. Acridine analogues bearing a free carboxylic group can serve as effective fluorescent probes in conformation analysis of peptides.Faculty of Chemistry, University of Gdansk, Sobieskiego 18 80-952, Gdansk, Poland; e-mail: neta@chemik.chem.univ.gda.pl Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 914–921, July, 2000.     

Synthesis and solvent-dependent photophysics of a novel fluorescent triazole-coumarin-based dye

Synthesis of a new coumarin-triazole-based dye and its photophysical parameters such as absorption, fluorescence emission, and fluorescence quantum yield were investigated. Studies have shown that the present dye has symmetry with a mirror image, especially in the ethanol solvent, with respect to the absorption and fluorescence spectra. As a result of the UV-vis and fluorescence spectroscopy techniques used, it was determined that absorption and emission spectra were shifted to the red with increasing solvent polarity. In addition, the spectral data of the synthesized compound exhibited that the stokes shifts are small, usually less than 50 nm, and the quantum yields are significantly high. In accordance with the results obtained, it can be stated that this novel dye synthesized here can offer an insight into application in sensor applications as analytical or biosensors, optoelectronic devices, and medicine industry.     

Synthesis and photophysics of a linear non-covalently linked porphyrin-fullerene dyad

The synthesis and characterization of a new pyridinofullerene ligand capable of forming axially symmetric complexes with ZnTPP is reported; molecular modelling studies, 1H NMR, UV-Vis spectroscopy and fluorescence quenching data support formation of a strong complex between the new ligand and ZnTPP.     

Synthesis of single-phase anatase nanocrystallites at near room temperatures

Single-phase aqueous solutions of nanocrystalline anatase titanium dioxide were produced under ambient pressure and at a temperature as low as 38 degree C using the sol-gel process.     

Synthesis and photophysics of red emitting RNA templated PbSe nanostructures

The presence of excess Pb(2+) in the building block consisting of RNA-mediated PbSe QDs induces polarization in PbSe resulting in an increased red fluorescence associated with enhanced charge separation and supramolecular interactions between different building blocks to produce nanotubular morphology in self-assembly.     

Synthesis of new ESIPT-fluorescein: photophysics of pH sensitivity and fluorescence

ESIPT-inspired benzimidazolyl substituted fluorescein dyes were synthesized. PH-sensitivity was determined by the photophysical property measured at a physiological possible pH range. Fluorescence quantum efficiency values were calculated independently at two different emissions. A rational relationship is defined between fluorescence quantum efficiency and calculated HOMO energy.     

Synthesis and photophysics of benzotexaphyrin: a near-infrared emitter and photosensitizer

Texaphyrins are pentaazadentate macrocycles with interesting photophysical properties and potential applications as nonlinear optical (NLO) materials, photosensitizers, magnetic resonance imaging (MRI) contrasting reagents, and radiation sensitizers, etc. To further red-shift the Q-like band of the texaphyrins, a benzotexaphyrin with an extensively delocalized pi-electron system was synthesized for the first time. Its photophysical characteristics were systematically investigated. Due to the extended pi-conjugation, the Q(0,0) band of benzotexaphyrin bathochromically shifts to 810 nm, and it emits at 825 nm with a singlet excited-state lifetime of 895 ps. Its triplet excited-state energy is estimated to be 119 kJ/mol. The triplet excited-state lifetime is approximately 2.2 micros, and the quantum yield of the triplet excited-state formation is 0.78. It also exhibits a triplet-triplet transient absorption in the region 505-590 nm. In addition, benzotexaphyrin exhibits high efficiency in generating singlet oxygen in methanol (Phi(Delta) = 0.65). Therefore, benzotexaphyrin could potentially be a NIR photosensitizer and emitter for photodynamic therapy and bioimaging applications.     

Polyfluorenes containing pyrazine units:Synthesis,photophysics and electroluminescence

A series of conjugated copolymers of 9,9-dioctylfluorene and symmetrical pyrazine unit (BY) were synthesized by Suzuki copolymerization and were used as novel light-emitting materials in PLEDs.Efficient energy transfer was observed in both thin film and solution.Compared with the lowest occupied molecular orbital (LUMO) energy level of the polyfluorenes homopolymer (PFO),the lower LUMO energy levels of copolymers indicated that the introduction of the BY unit would be benefit to electron injection.The turn-...     

Synthesis and photophysics of an octathioglycosylated zinc(II) phthalocyanine

A water soluble zinc(II) phthalocyanine symmetrically appended with eight thioglucose units was synthesized from commercially available hexadecafluorophthalocyaninatozinc(II) by controlled nucleophilic substitution of the peripheral fluoro groups. The photophysical properties and cancer cell uptake studies of this nonhydrolysable thioglycosylated phthalocyanine are reported. The new compound has amphiphilic character, is chemically stable, and can potentially be used as a photosensitizer in photodynamic therapy.     

Synthesis and photophysics of porphyrin-fullerene donor-acceptor dyads with conformationally flexible linkers

The synthesis and photophysics of a series of porphyrin-fullerene (P-C₆₀) dyads in which the two chromophores are linked by conformationally flexible polyether chains is reported. Molecular modeling indicates the two moieties adopt a stacked conformation in which the two chromophores are in close proximity. Photoexcitation of the free base dyads in polar solvents such as tetrahydrofuran and benzonitrile, causes electron transfer (ET) to generate charge-separated radical pair (CSRP) states, which were directly detected using transient absorption (TA) techniques. In nonpolar solvents such as toluene, where CSRP states were not directly detected, fullerene triplet state states were formed, according to TA studies as well as singlet oxygen sensitization measurements. The low value of the quantum efficiency for sensitized formation of singlet molecular oxygen [O₂(¹Δ_g)] in toluene and chloroform indicates that singlet energy transduction to give H₂P-¹C₆₀*, followed by intersystem crossing to H₂P-³C₆₀* and energy transfer to ³O₂, is not the operative mechanism. Rather, a mechanism is proposed involving ET to give CSRP states followed by exergonic charge recombination to eventually generate fullerene triplets. Such a mechanism has been demonstrated experimentally for structurally related P-C₆₀ dyads. For the corresponding ZnP-C₆₀ dyads with flexible linkers, only photoinduced ET to generate long-lived CSRP states is observed. Photoinduced charge separation in these dyad systems is extremely rapid, consistent with a through space rather than through-bond mechanism. Charge recombination is up to three orders of magnitude slower, indicating this process occurs in the inverted region of the Marcus curve that relates ET rates to the thermodynamic driving force. These observations once again demonstrate the advantages of incorporating fullerenes as electron acceptor components in photosynthetic model systems.     

Polyfluorenes containing tetraphenylthiophene segments: Synthesis,photophysics, and electroluminescence

2,5‐Bis(4‐bromophenyl)‐3,4‐diphenylthiophene was synthesized from benzyl chloride and sulfur and through the subsequent bromination of the intermediate 2,3,4,5‐tetraphenylthiophene. It was condensed with 2,7‐dibromo‐9,9‐dihexylfluorene via a nickel‐mediated Yamamoto coupling reaction to afford a new series of statistical copolymers with various compositions. In addition, poly(9,9‐dihexylfluorene) (PF) was synthesized under the same conditions for comparison. All the polymers were soluble in common organic solvents such as tetrahydrofuran (THF), chloroform, and dichloromethane. Their glass‐transition temperatures increased with an increase in the tetraphenylthiophene (TPT) content in the polymers, and they were 63–149 °C. The solutions of the polymers in THF emitted intense blue light with a photoluminescence maximum at 418–440 nm and quantum yields of 0.32–0.62. Thin films of the polymers with TPT fractions lower than 20 mol % emitted blue‐green light with two well‐resolved peaks at 445 and 520 nm and an optical band gap of about 2.85 eV. A thin film of the polymer with aTPT fraction of 50 mol % emitted pure blue light with a maximum at 419 nm and an optical band gap of 3.28 eV. An enhancement of the light‐emitting‐diode brightness by a factor of ～8 with respect to that of PF was achieved in apolymer containing 5 mol % TPT. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4015–4026, 2006     

Synthesis and photophysics of a porphyrin-fullerene dyad assembled through Watson-Crick hydrogen bonding

A novel porphyrin-fullerene dyad assembled through Watson-Crick hydrogen bonds is described; this system undergoes photoinduced electron transfer upon irradiation with visible light to produce a charge separated state that is substantially longer lived than that of previous dyads of this type.     

Synthesis and photophysics of monodisperse co-oligomers consisting of alternating thiophene and perylene bisimide

A series of monodisperse oligomers consisting of alternating thiophene (T) and perylene bisimide (P), denoted as (TP)(n)T (n = 1, 2, 3, 6), were synthesized and photophysically characterized. The steady-state absorption and fluorescence spectra revealed that the low-energy P-derived band remains almost unchanged upon the increment of the number of the repeat unit n. This can be rationalized as a consequence of nearly orthogonal molecular geometry and highly-localized electron density at LUMO level based on DFT calculation. A drastic reduction of the fluorescence quantum yields (Φ(F)) of (TP)(n)T was observed with the sequence of (TP)(6)T > (TP)(3)T > (TP)(2)T > (TP)(1)T, as compared to the parent perylene bisimide. Further femtosecond transient absorption studies clarified that the quenching mechanism is intramolecular electron transfer, in which the generated P radical anion was spectrally recognized. The rate of charge separation was found to be on the order of 10(11) s(-1), suggesting an efficient electron transfer reaction between the thiophene and perylene units. Interestingly, the charge separation rate constant increased more than three times upon the increment of n, whereas the charge-recombination rate constant remained almost unchanged at (1.58-2.21) × 10(9) s(-1). Analysis of the kinetic and thermodynamic data using the Marcus approach showed that the enhanced electronic coupling is the origin of the acceleration of electron-transfer reaction in the D-A copolymers.     

Synthesis and photophysics of dibenz[a,c]phenazine derivatives

The synthesis of dipolar dibenz[a,c]phenazine (DBP) derivatives is described. The compounds possess little electronic communication between donor and acceptor units in the ground state regardless of the pattern of substitution. The dipolar derivatives deactivate mostly via electron transfer (eT) under polar conditions. Intersystem crossing is likely to compete for S(1) relaxation.     

Synthesis and photophysics of silicon phthalocyanine-perylenebisimide triads connected through rigid and flexible bridges

Three new bisperylenebisimide-silicon phthalocyanine triads [(PBI)(2)-SiPcs 1, 2, and 3] connected with either rigid or flexible bridges were synthesized and characterized. A new synthetic approach to connect SiPc and PBI moieties through click chemistry produced triad 3 with an 80% yield. In (PBI)(2)-SiPc 1, PBI and SiPc are orthogonal and were connected with a rigid connector; triads 2 and 3 bear flexible aliphatic bridges, resulting in a tilted (2) or nearly parallel arrangement (3) of PBI and SiPc. Photoinduced intramolecular processes in these (PBI)(2)-SiPcs were studied and the results are compared with those of the reference compounds SiPc-ref and PBI-ref. The occurrence of electron-transfer processes between the SiPc and PBI units was confirmed by time-resolved emission and transient absorption techniques. Charge-separated (CS) states with lifetimes of 0.91, 1.3 and 2.0 ns for triads 1, 2, and 3, respectively, were detected using femtosecond laser flash photolysis. Upon the addition of Mg(ClO(4))(2), an increase in the lifetime of the CS states to 59, 110 and 200 μs was observed for triads (PBI)(2)-SiPcs 1, 2, and 3, respectively. The energy of the CS state (SiPc(·+)-PDI(·-)/Mg(2+)) is lower than the energy of both silicon phthalocyanine ((3)SiPc*-PDI) and perylenebisimide (SiPc-(3)PDI*) triplet excited states, which decelerates the metal ion-decoupled electron-transfer process for charge recombination to the ground state, thus increasing the lifetime of the CS state. The photophysics of the three triads demonstrate the importance of the rigidity of the spacer and the orientation between donor and acceptor units.     

Synthesis of highly crystalline and monodisperse maghemite nanocrystallites without a size-selection process.

The synthesis of highly crystalline and monodisperse gamma-Fe(2)O(3) nanocrystallites is reported. High-temperature (300 degrees C) aging of iron-oleic acid metal complex, which was prepared by the thermal decomposition of iron pentacarbonyl in the presence of oleic acid at 100 degrees C, was found to generate monodisperse iron nanoparticles. The resulting iron nanoparticles were transformed to monodisperse gamma-Fe(2)O(3) nanocrystallites by controlled oxidation by using trimethylamine oxide as a mild oxidant. Particle size can be varied from 4 to 16 nm by controlling the experimental parameters. Transmission electron microscopic images of the particles showed 2-dimensional and 3-dimensional assembly of particles, demonstrating the uniformity of these nanoparticles. Electron diffraction, X-ray diffraction, and high-resolution transmission electron microscopic (TEM) images of the nanoparticles showed the highly crystalline nature of the gamma-Fe(2)O(3) structures. Monodisperse gamma-Fe(2)O(3) nanocrystallites with a particle size of 13 nm also can be generated from the direct oxidation of iron pentacarbonyl in the presence of oleic acid with trimethylamine oxide as an oxidant.     

Synthesis, structures and photophysics of novel luminescent platinum–copper complexes

The novel hexanuclear platinum–copper complex [Pt₂Cu₄(C₆F₅)₄(CC^tBu)₄(acetone)₂] (1) and the polynuclear derivative [PtCu₂(C₆F₅)₂(CCPh)₂]_x (2), which crystallises in acetone as [Pt₂Cu₄(C₆F₅)₄(CCPh)₄(acetone)₄] (2)·(acetone)₄, have been prepared using [cis-Pt(C₆F₅)₂(THF)₂] and the corresponding copper–acetylide [Cu(CCR)]_x (molar ratio 1:2) as starting materials. Treatment of 1 and 2 with 2,2′-bipyridine (molar ratio Cu–bipy 1:1), afforded the new trinuclear derivatives [{cis-Pt(C₆F₅)₂(μ-CCR)₂}{Cu(bipy)}₂] (R=^tBu 3, Ph 4), in which the dianionic 3-platina-1,4-diyne acts as a didentate bridging ligand to two different cationic Cu(bipy) units through η²-side-on coordination of the alkynyl fragments. While similar treatment of 1 with dppe (Cu–dppe 1:1) yielded [{cis-Pt(C₆F₅)₂(μ-CC^tBu)₂}{Cu(dppe)}₂] (5), the analogous reaction of 2 with dppe afforded a mixture of complexes containing [Pt(C₆F₅)(CCPh)(dppe)] as the main platinum compound. The crystal structures of 1, 2·(acetone)₄, 3 and 4 and the luminescent behaviour of all complexes have been determined. A comparison of the photoluminescent spectra of 1 and 2 with those of the related platinum–silver species [PtAg₂(C₆F₅)₂(CCR)₂]_x and the monomeric [cis-Pt(C₆F₅)₂(CCR)₂]²⁻ suggests the presence of emitting states bearing a large cluster [PtM₂]_x-to-ligand (alkynide) charge transfer (CLCT).     

Synthesis and photophysics of novel 8-hydroxyquinoline aluminum metal complex with fluorene units

A novel luminescent metal complex, (MQPF)3Al2, with 8-hydroxyquinoline aluminum and 9,9-diphenylfluorene was synthesized. The optical properties were investigated by UV-vis absorption and fluorescence emission spectra. The results showed that the luminescence quantum yield of (MQPF)3Al2 was 0.612 in THF and it emitted red light with the band gap of 3.18 eV estimated from the onset absorption. The emission spectra exhibited obvious solvent effect. With the increase of polarity of solvents the fluorescence spectra changed obviously and appeared blue shift about 60 nm at room temperature. In addition, the light-emitting can be quenched by both electron donor (N,N-dimethylaniline) and electron acceptor (Fullerene), where the processes followed the Stern-Volmer equation. However, when adding 1,4-dicyanobenzene (DCB) which was a stronger electron acceptor to the solution of (MQPF)3Al2, the fluorescent intensity was increased.