Time resolved emission spectroscopy of poly(2,5-dicyano-p-phenylene-vinylene) films

Abstract

Filmes finos de poli(2,5-diciano-p-fenileno vinileno), DCNPPV, foram produzidos por síntese eletroquímica com variação do potencial aplicado de -0,15 até -1,0 V, e depositados sobre camada fina de ouro sobre vidro. A cinética de estado excitado destes materiais foi investigada por medidas de decaimentos de fluorescência. Os filmes apresentam decaimentos com três componentes, uma rápida da ordem de 200-400 picossegundos, e outra duas componentes de aproximadamente um e cinco nanossegundos, na temperatura de 293 K. O decaimento de fluorescência ocorre pela desativação em sítios de baixa energia na cadeia polimérica conjugada e por supressão do estado excitado por monômeros bromados terminais da cadeia e íons brometo aprisionados durante o crescimento eletroquímico do filme. A mudança do ânion do eletrólito suporte de brometo para perclorato reduziu de modo significativo essa contribuição de supressão do estado excitado como resultado da troca iônica por uma espécie não supressora.Films of poly (2,5-dicyano-p-phenylene vinylene), DCNPPV, were obtained by electrochemical synthesis over gold thin layer (20 nm) transparent electrode deposited on a glass plate. The DCNPPV films of 4 m thickness were produced by electropolymerization process of , , ´, ´-tetrabromo-2-5-dicyano-p-xilene at different applied potentials ( 0.15, 0.25, 0.40, 0.60, 0.80, and 1.0 V) using 0.1 mol L -1 of tetraethylammonium bromide in acetonitrile as the supporting electrolyte. The emission decays have three exponential components: a fast component in the picosecond range (200-400 ps), and two other of about one and five nanoseconds at 293 K. The fluorescence quenching process seems to occur by exciton trapping in a low-energy site and quenching by residual bromine monomer attached at the end of the polymer chain. However, the electrochemical synthesis generates entrapped bromide or ion pairs during the growth step of the film which also contributes to the deactivation. The change of the electrolyte from bromide to perchlorate reduces significantly this additional quenching effect by allowing ion exchange of formed bromide with the nonquenching perchloride anion.

Evaluation of the photocurrent value for poly(2,5-dicyano- p -phenylene-vinylene)-co-(p-phenylene-vinylene) (DCN-PPV/PPV)

“…This may be because cyano groups attached to the aromatic ring can reduce the LUMO level without too much change to the HOMO level. 9, reducing the rate of recombination and leading to greater photocurrent generation [28]. Figure 7 shows the cyclic voltammograms of PPV/ZnO, PPV/TiO 2 , DCN-PPV/PPV/ZnO, and DCN-PPV/PPV/TiO 2 composite films.…”

Ultrathin films of poly(2,5-dicyano- p -phenylene-vinylene)-co-( p -phenylene-vinylene) DCN-PPV/PPV: A Langmuir and Langmuir-Blodgett films study

“…The cyano group can occupy different relative positions in the PPV chain, being important the fact that the introduction of this group in the vinylene unit reduces the LUMO energy without significantly change of the absorption [20]. However, the influence in the backbone promotes a weak steric interaction between adjacent units, which in some cases may cause a blue-shift effect, maintaining their electron transport properties and keeping emissions efficient at longer wavelengths in the visible spectra [21,22]. In this sense, they have been synthetized in alternative ways to reach better operation lifetimes in order to better manipulate their photoluminescent (PL) and electroluminescent (EL) properties [22,23].…”

“…However, the influence in the backbone promotes a weak steric interaction between adjacent units, which in some cases may cause a blue-shift effect, maintaining their electron transport properties and keeping emissions efficient at longer wavelengths in the visible spectra [21,22]. In this sense, they have been synthetized in alternative ways to reach better operation lifetimes in order to better manipulate their photoluminescent (PL) and electroluminescent (EL) properties [22,23]. One specific application reported for DCN-PPV is the fact that perchlorate reduces significantly possible quenching effects by allowing ion exchange of formed bromide with the nonquenching perchloride anion [22], which can be have implications on the properties of this polymer when immobilized on solid supports.…”

“…In this sense, they have been synthetized in alternative ways to reach better operation lifetimes in order to better manipulate their photoluminescent (PL) and electroluminescent (EL) properties [22,23]. One specific application reported for DCN-PPV is the fact that perchlorate reduces significantly possible quenching effects by allowing ion exchange of formed bromide with the nonquenching perchloride anion [22], which can be have implications on the properties of this polymer when immobilized on solid supports.…”

Experimental and Theoretical Study of the Reaction Kinetics of 2,5-Dimethylterephthalonitrile Bromination Compared to 1,4-Dimethylbenzene Bromination

“…10 Moreover, it is used to obtain PPV polymers (polyphenylenevinylene) through electrosynthesis; such polymers have been drawing the attention of researchers since the 1990s because their properties allow them to be used in organic light-emitting diodes (OLEDs), organic photovoltaic films (OPVs), and in photovoltaic cells. 11 The 2,5-dicyano-p-xylene compound was converted into α,α,α′,α′-tetrabromide-2,5-dicyano-p-xylene, which has been studied as part of the search for conducting polymers with well-defined properties to be used in photovoltaic devices 12 and photoluminescent materials, among others. 13 In this study we aimed to compare the bromination reactions that occur in 1,4-dimethylbenzene and in 2,5-dimethylterephthalonitrile.…”