Ernesto Rivera

Novel polyacetylenes containing pendant 1-pyrenyl groups: synthesis, characterization, and thermal and optical properties

Abstract We report the synthesis as well as the thermal, optical and photophysical properties of four different polyacetylenes with pendant 1-pyrenyl groups: poly(1-ethynylpyrene) (PEP), poly(1-(trimethylsilanylethynyl)pyrene) (PTMSEP), poly(1-(4-(trimethylsilanyl-buta-1,3-diynyl)pyrene) (PTMSBDP) and poly(1-buta-1,3-diynylpyrene) (PBDP). Polymerizations were carried out with W and Ta catalysts, respectively, for mono- and disubstituted monomers. Soluble poly(1-ethynylpyrene) with high molecular weights (up to 4×10 5 ) and extended conjugation of the main chain was obtained with good yields. Lower molecular weights (up to 6×10 3 ) were obtained with the other polymers. Oligomers and polymers displayed high thermal stability. From the absorption spectra of the various polymers, it is found that PEP possesses a higher degree of conjugation than the other polyacetylenes. Molecular interactions occur between pyrene units present in each polymer giving rise to an emission due to associated pyrenes. These interactions are affected by the steric hindrance present in the polymer backbone. Excitation spectra combined with fluorescence decay profiles show that these interactions occur in the ground state (excited complex).

Synthesis and Characterization of Novel Pyrene-Dendronized Porphyrins Exhibiting Efficient Fluorescence Resonance Energy Transfer: Optical and Photophysical Properties

A novel series of pyrene dendronized porphyrins bearing two and four pyrenyl groups (Py(2)-TMEG1 and Py(4)-TMEG2) were successfully synthesized. First and second generation Fréchet type dendrons (Py(2)-G1OH and Py(4)-G2OH) were prepared from 1-pyrenylbutanol and 3,5-dihydroxybenzyl alcohol. These compounds were further linked to a trimesitylphenylporphyrin containing a butyric acid spacer via an esterification reaction to obtain the desired products. Dendrons and dendronized porphyrins were fully characterized by FTIR and (1)H NMR spectroscopy and their molecular weights were determined by matrix-assisted laser desorption ionization time of flight mass spectrometry. Their optical and photophysical properties were studied by absorption and fluorescence spectroscopies. The formation of dynamic excimers was detected in the pyrene-labeled dendrons, with more excimer being produced in the higher generation dendron. The fluorescence spectra of the pyrene dendronized porphyrins exhibited a significant decrease in the amount of pyrene monomer and excimer emission, jointly with the appearance of a new emission band at 661 nm characteristic of porphyrin emission, an indication that fluorescence resonance energy transfer (FRET) occurred from one of the excited pyrene species to the porphyrin. The FRET efficiency was found to be almost quantitative ranging between 97% and 99% depending on the construct. Model Free analysis of the fluorescence decays acquired with the pyrene monomer, excimer, and porphyrin core established that only residual pyrene excimer formation in the dendrons could occur before FRET from the excited pyrene monomer to the ground-state porphyrin core.

Polymers from coumarines: 4. Design and synthesis of novel hyperbranched and comb-like coumarin-containing polymers

Abstract Novel monomers containing coumarin groups [2-(7-Cumarinyloxy)Oethoxy]dimethyl terephthalate and [6-(3-carboxy)coumarinyl] diacetylhydroquinone were synthesized and polymerized by high temperature polycondensation to give hyperbranched and comb-like coumarin-containing polymers. All polymers were completely soluble in chlorinated aliphatic hydrocarbons and showed M n in the range of 2000–50000 and gave film of good optical quality on casting from solution. All polymers except one were amorphous with T g in the range of 100–230°C and thermostability of 370–415°C. All polymers were found to be blue emitters emitting light in the range 450–492 nm.

Synthesis and Characterization of Novel Amphiphilic Azo-Polymers Bearing Well-Defined Oligo(Ethylene Glycol) Spacers

Four novel azo-polymers bearing oligo(ethylene glycol) spacers were synthesized and characterized. Monomers were prepared by esterification of the RED-PEG dyes previously synthesized by us: N-methyl-N-{4-[(E)-(4-nitrophenyl)diazenyl]phenyl}-N-(5-hydroxy-3-oxapentas-1-yl)amine (RED-PEG-2), N-methylN-{4-[(E)-(4-nitrophenyl)diazenyl]phenyl}-N-(8-hydroxy-3,6-dioxaoctas-1-yl)amine (RED-PEG-3), N-methyl-N-{4-[(E)-(4-nitrophenyl)diazenyl]phenyl}-N-(11-hydroxy-3,6,9-trioxaundecas-1-yl)amine (RED-PEG-4) and N-methyl-N-{4-[(E)-(4-nitrophenyl)diazenyl]phenyl}-N-(17-hydroxy-3,6,9,12,15-pentaoxaheptadecas-1-yl)amine (RED-PEG-6) with methacryloyl chloride. The obtained monomers (nPEGMAN series) were polymerized in the presence of AIBN in THF to give the corresponding azo-polymers (pnPEGMAN series). Also, Langmuir films were prepared with these polymers; the obtained monolayers exhibited good reversible behavior upon successive compression/expansion cycles.

Polypeptides with pendant porphyrins of defined sequence of chromophores: towards artificial photosynthetic systems

In this paper we now report our ongoing progress in the preparation of artificial photosynthetic systems through the preparation of light harvesting multi-porphyrins. A tetramer, constituted of a central dipeptide functionalized by two free-base porphyrins and surrounded by one amino-acid bearing a pendant Zn(II) porphyrin on each side, has been chosen. The optical and photophysical properties of this tetramer have been studied by absorption and fluorescence spectroscopy. In addition, the energy transfer phenomenon has been studied and monitored by femtosecond time-resolved fluorescence. Our results indicate that the excited state dynamics redounding in the excitation being localized in the inner free-base porphyrins takes place in the time scale of approximately 1 ps.

Fréchet-type dendrons bearing azobenzene units and flexible oligo(ethylene glycol) spacers: synthesis, characterization, thermal and optical properties

In this study, we report the synthesis and characterization of a novel series of first- and second-generation Fréchet-type dendrons bearing amino-nitro, amino-methoxy and amino-butyl substituted azobenzene units and tetra(ethylene glycol) spacers. These compounds were fully characterized by FTIR, 1H and 13C NMR spectroscopies, and their molecular weights were determined by MALDITOF. The thermal properties of the obtained dendrons were studied by thermogravimetric analysis and differential scanning calorimetry and their optical properties by absorption spectroscopy in solution. Molecular calculations were performed in order to determine the dipole moment of these molecules. Some of the dendrons showed a liquid crystalline behaviour, which was studied by light polarized microscopy as a function of the temperature in order to determine the transition temperatures and the structure of the mesophase.

Luminescent polythiophenes-containing porphyrin units: synthesis, characterization, and optical properties

A novel thiophene monomer containing a meso-tetraphenylporphyrin (MTPP) unit linked via an alkyl spacer was synthesized and characterized. This monomer was copolymerized in the presence of 3-dodecylthiophene (MDT) in different ratios MTPP: MDT (1:2, 1:4, and 1:6), using FeCl3 as oxidizing agent, to give the corresponding copolymers (CP12, CP14, and CP16). In addition, MTPP and MDT were also homopolymerized under the same reaction conditions to give homopolymers PTPP and PDT, respectively. The obtained compounds were characterized by FTIR and 1H NMR spectroscopy. The optical properties of the polymers were studied by absorption and fluorescence spectroscopy in THF solution. All polymers exhibited the typical absorption bands of the porphyrin: a Soret band at λ = 422 nm and four Q-bands between λ = 500–700 nm. Moreover, an additional band was observed at λ = 328 nm, due to the polythiophene backbone. CP14 and CP16 showed intense emission in the region between λ  = 550–800 nm.

Synthesis and characterization of novel polymers bearing fluorescein units: thermal and optical properties

In this work, we report the synthesis and characterization of four novel series of copolymers bearing fluorescein moieties. Two monomers: fluorescein methacrylate and dimethacrylate were prepared and were copolymerized in the presence of four different acrylic monomers bearing oligo(ethylene glycol) segments: ethylene glycol phenyl ether acrylate, ethylene glycol phenyl ether methacrylate, poly(ethylene glycol) methyl ether acrylate (Mn = 475 g/mol), and poly(ethylene glycol) methyl ether methacrylate (Mn = 480 g/mol). The obtained copolymers were fully characterized by Fourier Transform Infrared Spectroscopy (FTIR) and Proton Nuclear Magnetic Resonance (1H NMR) spectroscopy. Their thermal properties were determined by thermogravimetric analysis and differential scanning calorimetry, and their optical properties were studied by absorption and fluorescence spectroscopy in solution and in solid state.

Synthesis and Characterization of Novel Polythiophenes Containing Pyrene Chromophores: Thermal, Optical and Electrochemical Properties

A novel series of pyrene containing thiophene monomers TPM1–5 were synthesized and fully characterized by FTIR, MS, 1H- and 13C-NMR spectroscopy; their thermal properties were determined by TGA and DSC. These monomers were chemically polymerized using FeCl3 as oxidizing agent to give the corresponding oligomers TPO1–5) and they were electrochemically polymerized to obtain the corresponding polymer films deposited onto ITO. All oligomers exhibited good thermal stability, with T10 values between 255 and 299 °C, and Tg values varying from 36 to 39 °C. The monomers showed an absorption band at 345 nm due to the S0 → S2 transition of the pyrene group, whereas the fluorescence spectra showed a broad emission band arising from the “monomer” emission at 375–420 nm. The obtained polymers exhibited two absorption bands at 244 and 354 nm, due to the polythiophene and the pyrene moieties, respectively. The fluorescence spectra of polymers showed a broad “monomer” emission at 380–420 nm followed by an intense excimer emission band at 570 nm, due to the presence of intramolecular pyrene-pyrene interactions in these compounds.

Synthesis and characterization of novel dendrons bearing amino-nitro-substituted azobenzene units and oligo(ethylene glycol) spacers: thermal, optical properties, Langmuir blodgett films and liquid-crystalline behaviour.

In this work, we report the synthesis and characterization of a novel series of first and second generation Fréchet type dendrons bearing amino-nitro substituted azobenzene units and tetra(ethylene glycol) spacers. These compounds were fully characterized by FTIR, 1H and 13C-NMR spectroscopies, and their molecular weights were determined by MALDI-TOF-MS. The thermal properties of the obtained dendrons were studied by TGA and DSC and their optical properties by absorption spectroscopy in solution and cast film. Molecular calculations were performed in order to determine the optimized geometries of these molecules in different environments. Besides, Langmuir and Langmuir Blodgett films were prepared with the first generation dendrons that were shown to be amphiphilic. Finally, some of the dendrons showed a liquid crystalline behaviour, which was studied by light polarized microscopy as a function of the temperature in order to determine the transition temperatures and the structure of the mesophase.