Pietro Bortolus

Photochemistry of tris(2,2′-bipyridine)ruthenium(II) in chlorinated solvents

The photolysis of tris(2,2′-bipyridine)ruthenium(II) in chlorinated solvents at 436 nm and room temperature leads to the formation of cis-dichlorobis-2,2′-bipyridine)ruthenium(II) and 2,2′-bipyridine as the main products.

Photochemical behaviour of poly-(organophosphazenes)—II. Oxygen influence on the photodegradation of aryloxy- and arylamino-substituted polyphosphazenes in solution

Abstract The photodegradations of poly-[bis(β-naphthoxy)] phosphazene and poly-[bis(p-tolylamino)] phosphazene were investigated in methylene chloride solution. A mechanism has been proposed to explain the influence of molecular oxygen on the photoprocesses. Molecular weight variations, results of flash photolysis experiments and the observed post-photochemical effect are in agreement with the suggested mechanism.

Phosphazene-bound Rose Bengal: A novel photosensitizer for singlet oxygen generation

In this paper we report the synthesis and the characterization of cyclo- and polyphosphazenes supporting Rose Bengal. These substrates are suitable for the photosensitized generation of singlet oxygen, both in homogeneous and in heterogeneous phase. The efficiency of1O2 production has been measured in homogeneous solution using, as photosensitizer, the cyclophosphazene-bound Rose Bengal and considering, as testing reaction, the oxidation of 1,3-diphenylisobenzofuran; it was found comparable to that of free Rose Bengal in the same experimental conditions.

Photochemical behaviour of poly(organophosphazenes)—part VII. direct and sensitized photochemistry of poly[bis(4-isopropylphenoxy)]phosphazene in solution and in film

Abstract The direct and benzophenone-sensitized photochemistries of poly[bis(4-isopropylphenoxy)]phosphazene (PIPP) have been investigated both in solution and in film. It has been found that the presence or the absence of molecular oxygen during photolysis in solution is an important factor in inducing degradation or crosslinking, respectively, of the irradiated polymer. By contrast, during photochemistry of the polyphosphazene film, photocrosslinking is always the major process, accompanied by formation of hydroperoxides and carbonylic groups when the experiments are carried out in air. The benzophenone-sensitized hydroperoxide formation on PIPP films may be an important process for subsequent surface grafting on the polyphosphazene matrix.

Ultraviolet functionalization of poly[bis(4-isopropylphenoxy)]phosphazene surfaces: An infrared and a sims study

Abstract Films of poly[bis(4-isopropylphenoxy)phosphazene] (PIPP) have been irradiated in air with u.v. light, and the exposed polymer surface investigated by i.r. spectroscopy and secondary ion mass spectrometry. Evidence is given that light-generated hydroperoxides are formed mainly on the tertiary carbons of the isopropylic groups in the polyphosphazene. These functions may be used for surface functionalization studies of PIPP.

Photochemical behaviour of poly(organophosphazenes)—Part VIII. Further investigations on the sensitized photochemistry of poly[bis(4-isopropylphenoxy)phosphazene]

Abstract The photochemistry of poly[bis(4-isopropylphenoxy)phosphazene] (PIPP) sensitized by hexakis(4-benzoylphenoxy)cyclophosphazene and by poly[bis(4-benzoylphenoxy)phosphazene] was investigated both in solution and in film. Air-equilibrated CH2Cl2 solutions of this polymer, also containing the above-mentioned benzophenone-containing phosphazene substrates, were irradiated with light absorbed exclusively by the carbonyl substituent. The irradiation causes a sharp decrease of the viscosity, attributed to chain scission of the PIPP backbone. In this process the solvent plays a key role. On the other hand, no photochemical change was observed for the same pair of molecules in the solid state. X-ray diffraction studies and DSC investigations on PIPP films, doped with benzophenone-substituted cyclo- or poly-phosphazenes, reveal that the lack of photoreactivity is due to phase segregation in these systems.

Aryloxy-substituted cyclophosphazenes: a new class or intramolecular excimers

Abstract Hexa-aryloxy-substituted cyclophosphazenes show eximer emission due to intramolecular interaction. Values of the excimer stabilization energy and activation energy of exeimer formation have been obtained. The effect of steric hindrance on excimer formation has been examined for p -alkyl-substituted hexa-phenoxy-cyclophosphazenes.

Photochemical behavior of poly(organophosphazenes). XI. Photochemistry of poly[bis(4-benzylphenoxy) phosphazene]

In this paper we present results on the photolysis of poly[bis(4-benzylphenoxy)-phosphazene] in solution and in film, both in the presence and in the absence of molecular oxygen. Light irradiation of the polymer in oxygen-saturated CH2Cl2 solutions results in a remarkable degradation of the polyphosphazene, while in argon-purged solutions no appreciable variations of the polymer structure could be detected. The photolysis of poly[bis(4-benzylphenoxy)phosphazene] in films induces the cross-linking of the polymer regardless of the presence or the absence of molecular oxygen. The main process observed during the photochemistry both in solution and in the solid state of the polymer is the oxidation of the 4-benzylphenoxy group on the polyphosphazene, without involvement of the inorganic -P=N- backbone. The effect of temperature on the photolysis of the polyphosphazene substrate in film is also reported.

Photolysis of polystyrene in halocarbons. Evidence for the involvement of a charge-transfer interaction in the photochemical degradation

Abstract The rate of the photo-oxidative degradation of polystyrene in halomethanes increases in the order: methylene chloride