The synthesis, spectro-electrochemical study, and electrochemical polymerization of bis(diphenylamino) substituted ferrocenes (Fcs), including the family of the 1,3,4-oxadiazole (OXD) bridged 1,1′-[p-(Ph 2 N)(C 6 H 4 ) n OXD] 2 Fc and the vinylene bridged ferrocene 1,1′-[p-(Ph 2 N)(C 6 H 4 )-(E)-CHdCH] 2 Fc, have been carried out. The ferrocene compounds underwent three stepwise one-electron oxidations to form the (3+) radical cations that further electrochemically polymerized on a Pt or an indium tin oxide (ITO) electrode surface. The polymeric layers showed extremely good hole-injection properties. The polymeric light emitting devices (PLEDs) of ITO/ED-1,1′-[Ph 2 N(C 6 H 4 ) 3 OXD] 2 Fc/PVK:Ir(PPy) 3 :PBD/Mg-Ag showed a turn-on voltage (at 100 cd/m 2 ) of 11 V, with a maximum brightness of 27 700 cd/m 2 . The turn-on voltage was 1.5 V lower than that of the poly(3,4-ethylenedioxythiophene)poly(styrenesulfonate) based PLED and 2 V lower than the corresponding electrochemically deposited poly(4-(N,N-diphenylamino)styrene) based PLED.
Under UV irradiation, 1,4-bis(5-(4-octan-2-ylphenyl)-1,3,4-oxadiazol-2-yl)naphthalene (NOXD) and poly(fluorenetolyldiphenylamine) (PFT) are blue light emissive in solid film. When NOXD and PFT were blended to form a neat thin-film, yellowish exciplex emission was observed. The emissive properties vary when the materials were blended into different kinds of polymeric hosts; while polystyrene-NOXD-PFT (5 : 1 : 1) and PMMA-NOXD-PFT (5 : 1 : 1) showed blue light emission, poly(acrylonitrile-co-methyl acrylate) (P(AN-co-MA))-NOXD-PFT (5 : 1 : 1) showed blue and yellow dual emissions. When the film was heated at 140 C for 2 min, the yellow light exciplex emission was enhanced. However, upon cooling to ambient temperature, the exciplex emission intensity gradually dropped back. Similar thermofluoric behaviors were observed when the thermally crosslinked polyepoxy-polymercaptan-NOXD-PFT film (20 : 1 : 1) was heated at 160-170 C; the blue light emissive film showed yellow light emission, and turned white when cooling down to ambient temperature. This thermofluoric phenomenon is recyclable. We attributed the observation of the yellow emission to the segregation of NOXD from the polymeric host at high temperature that allows NOXD to aggregate with PFT, leading to exciplex emission.
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