Poly N-vinylcarbazole

In the case of undoped PVCa films, impurities and surface states dominate the photoconduction mechanism (6) leading one to question any study of intrinsic pKotoconduction in organic polymers. Poly(N-vinylcarbazole) films yellow under ambient laboratory conditions. Work in our laboratory (7) has shown that ageing of a purified sample of PVCa leads to an increase in photoresponse in the 350-450 nm region while there is an initial drop in photoresponse in the 250-... 

Fig. 9 (a) Molecular structures of novel ESIPT dyes, 2,5,-bis[5-(4-t-butylphenyl)-[l,3,4]oxadia-zol-2-yl]-phenol (SOX), and 2,5-bis[5-(4-t-butylphenyl)-[l,3,4]oxadiazol-2-yl]-benzene-l,4,-diol (DOX). (b) Emission colors in the Commission Internationale de L Eclariage (CEE) chromaticity diagram. The inner oval and the filled circle at coordinate (x,y) of (0.33, 0.33) indicate the white region and the ideal color, respectively. Note that PS and PVK denote polystyrene and poly (N-vinylcarbazole) film (reprint from ref. [91], Copyright 2005 Wiley-VCH)... 

WD Gill, Drift mobilities in amorphous charge-transfer complexes of trinitrofluorenone and poly-n-vinylcarbazole, J. Appl. Phys., 43 5033-5040, 1972. 

By fluorescence analyses just upon laser ablation and of ablated surface, Molecular aspects of ablation echanisa were elucidated and a characterization of ablated Materials was perforaed. Laser fluence dependence of poly(N-vinylcarbazole) fluorescence indicates the iaportance of Mutual interactions between excited singlet states. As the fluence was increased, a plasna-like eaission was also observed, and then fluorescence due to diatonic radicals was superinposed. While the polyner fluorescence disappeared Mostly during the pulse width, the radicals attained the naxinun intensity at 100 ns after irradiation. Fluorescence spectra and their rise as well as decay curves of ablated surface and its nearby area were affected to a great extent by ablation. This phenonenon was clarified by probing fluorescence under a Microscope. 

In the present work, we have examined poly(N-vinylcarbazole) (abbreviated hereafter as PVCz) and pyrene-doped poly(aethyl methacrylate) (PMMA) films by using a tine-resolved fluorescence spectroscopic aethod. Fluorescence spectra and their dynanic behavior of the forner fila were elucidated with a high intensity laser pulse and a streak camera, which nakes it possible to neasure dynaaics just upon laser ablation. This aethod reveals aolecular and electronic aspects of laser ablation phenomena (17). For the latter fila a laser pulse with weak intensity was used for characterizing the ablated and Basked areas. On the basis of these results, we demonstrate a high potential of fluorescence spectroscopy in aolecular studies on laser ablation and consider its mechanism. Experimental... 

Thermally stimulated hole current in poly-N-vinylcarbazole shows distinct maximum at around 5°C and another large current above 100°C. This 5°C maximum is due to 0.56 eV hole traps of 7 x 1015 cm 3 density. Photoconductivity in poly-N-vinylcarbazole increases appreciably when irradiated with UV-light in air at room temperature and this increase accompanies the formation of 0.56 eV hole traps. The nature of this traps has been discussed. 

Poly-N-vinylcarbazole is one of the very important organic photoconductors now in use in electrophotography. For practical use, a little amount of sensitizer is usually added. 

Another important problem of the photoconductivity of poly-N-vinylcarbazole is the carrier transport. With the so-called time of flight method this problem is well investigated. 

A very important progress has been made recently on the theoretical background of the analysis of the transport problem also (2). Although it has been made clear that multi-trapping process is determining the carrier transport in the polymer, not only the nature of the trap but also the trap depth and the trap population are not definitely known even in pure poly-N-vinylcarbazole. The present report concerns with this problem. 

So-called thermally stimulated current is the most direct method to investigate the nature of the traps, the current being due to the carriers comming out thermally from the traps. Although the thermally stimulated current of poly-N-vinylcarbazole has already been investigated by Pai (3) and Patora (4), the results are somewhat different. We investigated this problem with many... 

Figure 2. Thermally stimulated current of poly-N-vinylcarbazole film (i) The current observed for the first time without any pretreatment (ii) the same after this first measurement (collecting voltage 30V (Au- -) heating rate 3.3°C/min)...

Measurement of the thermally stimulated current of the poly-N-vinylcarbazole film irradiated prior to the measurement with UV-light in air at room temperature. 

Fig. 5 shows the thermally stimulated current of poly-N-vinylcarbazole measured with the above mentioned method. 

In this way, the trap depth of the poly-N-vinylcarbazole was calculated as aE =0.56 eV and from the area of the 5°C peak the trap density was estimated to be of the order of 7 x 10l3 cm-3. 

Figure 6. Typical experimental curve of the thermally stimulated current in poly-N-vinylcarbazole near 5°C peak...

Figure 7. Thermally stimulated current in poly-N-vinylcarbazole with different heating rates (1.7-6.7°C/min collecting voltage 30V (Au+)). Films were cleaned first ana UV illuminated for 20 min at —150°C in vacuo with the total light of the Hg lamp of Figure 3.

Various methods are proposed (5, a—g), (6). Among these, the methods in which monomolecular recombination or bimolecular recombination of the carriers are assumed could not be used in our case, because the carrier transport in poly-N-vinylcarbazole is known to be the multi-trapping process of the hole carrier. The values of the trap depthaE of 5°C peak by these several methods are summarized in Tab. 1. Values are widely scattered and it seemed that this is due to the approximations involved in the method of analysis. Our value is calculated by the... 

As well known, so-called excimer sites exist in poly-N-vinylcarbazole. It is well established that these excimer sites are the efficient traps for the singlet and triplet excitons, which migrate along the polymer chain. The structure of these sites are thought to be a special conformation having a pair of carbazolyl groups arranged parallel each other. 

A similar approach was used in grafting Cjq onto a pregenerated lithiated polyethylene surface [121]. A polyethylene film with terminal diphenylmethyl groups was deprotonated with BuLi to yield an anionic polyethylene surface that was treated with Cg0 and quenched with methanol. The incorporation at the polyethylene surface was determined by XPS, UV/Vis and fluorescence spectroscopy. This reaction also works for polyisopropene, polybutadiene [69], poly(vinylbenzyl chloride) or poly(N-vinylcarbazole) PVK [54] with BuLi or NaH as a base. Charge-transfer interactions in the soluble fullerene-PVK derivative between the positively charged carbazole and Cjq lead to an enhanced photoconductivity compared with PVK [54]. 

Lai YS, Tu CH, Kwong DL, Chen JS (2005) Bistable resistance switching of poly(N-vinylcarbazole) films for nonvolatile memory applications. Appl Phys Lett 87 (12) 122101-122103... 

Fig. 6. Relation between dark conductivity and concentration of doping compounds log Od = / (log nacceptor/ndye). (I) phthalocyanine-(-o-chloranil (2) poly-N-vinylcarbazole + o-chloranil...

Several such polymers have shown electrochromic behavior, among them poly(n-vinylcarbazole) [73] which switches from colorless in the neutral state to green in the doped state (Scheme 10) and poly(Ar-phenyl-2-(2 -thienyl)-5-(5"-vinyl-2"-thienyl)pyrrole) [74], which changes from yellow to reddish brown upon oxidation (Scheme 11). A study of the electrochromic properties of blends consist-... 

---