Steady state and transient photoluminescence in poly-p-phenylene vinylene films and nanofibers

Abstract

We report in this paper experimental data on steady state and transient photoluminescence of poly-p-phenylene vinylene in the form of nanofibers prepared with a template method and converted at 110 degrees C. Results are compared to those obtained from films of different thicknesses converted at the same temperature. Data are analyzed by a model of bimodal distribution of conjugation lengths and the photoluminescence band shapes, evaluated in the framework of this model, are also presented.

Photoluminescence properties of new PPV derivatives

“…From Table 1, the PPV film parameters t r ¼784 ps, t nr ¼ 183 ps, t mean ¼149 ps and QY ¼0.19 are in agreement with the values found in the literature [26,27]. The standard PPV film is characterized by long conjugated segments organized in well packed regions (formed in aggregated area) where polymer chains are close to each other [29].…”

“…(1), n 1 and n 2 are the populations of the excited state levels 1 and 2, respectively, and k 1 and k 2 are the inverse of the lifetimes t 1 and t 2 . In this simple model [26], the populations of levels 1 and 2 are coupled in order to account indirectly for a migration process from short to long segments [27]. The photogenerated charges populating the higher energy level 1 migrate toward defects and relax quickly on the lower energy state 2 with lifetime t 1 .…”

Photoluminescence properties of new poly(N‐vinylcarbazole)‐3‐methylthiophene (PVK‐3MeT) graft copolymer

“…For this sample the radiative lifetime τ r is in the order of nanosecond consistent with a fully allowed transition of a strongly absorbing molecule. This is characteristic of an emission process resulting mainly from singlet intrachain excitons 24. As in the case of PPV films, this is the photogeneration of singlet intrachain excited states24, 25 that seems to be the dominant product of the photoexcitations in this copolymer film.…”

“…Added to that, upon excitation the chemical structure presents a noncoplanar conformation 20. So, the probability of the formation upon photo‐excitation of the nonemissive excimers is reduced, while, the photo‐generation of the intrachain excitons with higher fluorescence efficiencies and longer fluorescence lifetime24, 26, 28 is favored in our copolymer. Consequently we notice an increase of the radiative pathway in our synthesized copolymer compared to that in polythiophenes systems.…”

“…These trends make us believe that the nonradiative process become less important in film and in solution compared to that in powder. In fact, focused studies on the optical properties of various PPV derivatives in different morphologic states (film, nanofiber…), show that the increase of the decay times is accompanied by the increasing of the QY efficiency,24, 25 and followed with an increase in the PL intensity. The some phenomena are observed in our case when going from PVK‐3MeT powder to PVK‐3MeT film and solution (Fig.…”