Investigation of the Photophysical Processes and Photochemical Reactions Involved in PVK Films Irradiated at λ > 300 nm

Abstract

This paper is devoted to the investigation of the phototransformation mechanisms of PVK exposed to long-wavelength radiations (λ > 300 nm) in the absence and in the presence of oxygen. PVK irradiated as thin films was analyzed by fluorescence, UV-vis, and IR spectroscopies. The photoproducts formed were identified by postirradiation treatments including chemical derivatization reactions and HPLC analysis. The cross-linking was evaluated by gel fraction measurements. PVK is known to give an intense excimer fluorescence and no monomer fluorescence. The phototransformations provoked by light absorption are shown to lead to a dramatic decrease of this fluorescence which can be correlated with the modification of the chemical structure of the macromolecules. The decrease of fluorescence is the result of the diminution of the local mobility of the macromolecular chains resulting from cross-linking reactions provoked by the recombination of the several radicalar species. A general mechanism accounting for the phototransformation of PVK in the presence and in the absence of oxygen is proposed.

Photocrosslinking of poly(N-vinylcarbazole): Implementing a complementary set of techniques to characterize the three-dimensional network formation

“…This result is in good agreement with the SSA is the specific surface area, V p is the porous volume and MaxPSD R p is the maximum of pore size distribution. first step of the mechanism proposed in our previous paper [9]. Secondly, the kinetics of disappearance of the C-N bond and growth of the T g present two distinct periods: until 50 h of exposure, the curve presents a rapid increase, and after 50 h, the lower slope of the curve indicates slighter modifications of the matrix.…”

“…Validation of the photocrosslinking mechanism: correlation of DSC and FTIR data As recalled above, the identification of the photoproducts allowed us to propose a mechanism of phototransformation of PVK involving in a first step the scission of the C-N bond [9]. In the present work the evolution of the C-N bond throughout exposure was directly monitored by infrared spectroscopy.…”

“…Poly(N-vinylcarbazole) (PVK) appeared as a good candidate since the mechanisms of photoageing of this polymer have been previously studied in detail [9]. It has been shown that the photodegradation mechanism of PVK was predominantly governed by crosslinking reactions (Scheme 1).…”

Characterization of the excimers of poly(N-vinylcarbazole) using TRANES

“…It is known that aromatic vinyl polymers like polystyrene [5,6], polyvinylnaphthalene [7] and poly(N-vinylcarbazole) [8] exhibit excimer fluorescence even in dilute solution and it is ascribed to the interaction of the nearby chromophores attached in the polymer backbone. Among these polymers, poly(N-vinylcarbazole) (PNVC) has attracted considerable attention due to its photoconducting properties [9]. Because of its high electroluminescence efficiencies PNVC has also been widely applied as an emission layer or a hole-transport layer in organic light emitting diodes (OLEDs) [10][11][12][13][14].…”

Photoinduced energy transfer in blend films of hole and electron transport materials

“…PVK has attracted considerable attention due to its specific electronic properties and photoconductive properties [5]. Containing the positive charge transporting carbazole pendant groups, PVK is now extensively used as the HTL and host material and is one of the most interesting materials in OLEDs [6][7][8][9].…”