By successive deposition of monolayers of the hexaalkoxytriphenylene derivative Te(OH)2, organized multilayers with a thickness between 18 and 360 Å can be obtained. Photoexcitation of the Langmuir-Blodgett films, deposited on interdigitating electrodes with a spacing of 100 μm, by a laser pulse of 4 ns full width at half maximum at a wavelength of 320 nm and with an energy between 5 and 200 μJ, induces transient photocurrents. At large applied fields or upon increasing the energy of the laser pulse and at reduced pressure, besides a transient current pulse of which the features are determined by the bandwidth of the experimental setup, a second current pulse grows in and shows a maximum at 1.5 μs after excitation. At low fields, charge generation occurs mainly in the bulk of the sample. In this field range, most charge carriers disappear by trapping or recombination before they can reach the opposite electrode, making it difficult to get information about the transit time. In the high field range, the charge carriers are still due to light absorbed by the Te(OH)2 layers. In this field range, the pressure of air or nitrogen strongly influences the features of the second maximum. The observation of the second maximum above a critical voltage and under optimal pressure conditions, suggests that corona discharging is also an important process. According to this model, the second maximum is related with the transit time of the charge carriers which migrate perpendicular to the substrate.
The electroluminescent properties of 5′-[4-[bis(4-ethylphenyl)amino]phenyl] -N,N,N′,N′-tetrakis(4-ethylphenyl) -[1,1′:3′,1″-terphenyl]-4,4″-diamine (pEFTP) were investigated in a vapor deposited layer and dispersed in a polymer matrix. Blue–violet electroluminescence was observed, after applying voltages beyond 12 V for the single layer devices and 22 V for the double layer devices. The electroluminescence (EL) spectrum shows two maxima, of which one corresponds to that of the photoluminescence spectrum. Either direct radiative recombination of the hole and the electron residing at two neighboring molecules or phosphorescence is causing this red shifted electroluminescence maximum. Transient electroluminescence measurements allow us to estimate the mobilities of the charge carriers in the different transport layers. The occurrence of an EL overshoot after switching off a voltage pulse, confirms the importance of detrapping and interfacial phenomena in the radiative recombination in pEFTP.
Langmuir−Blodgett (LB) films of an amphiphilic long-chain derivative of anthracene, of which the molecular packing shows a strong resemblance with the ab-plane of anthracene crystals, were investigated with respect to their photoconductive properties. Efficient photoinduced charge carrier generation and in-plane charge transport have been observed in LB-films of (2A7), using a gap configuration. The wavelength and intensity dependence of the quantum yield of the photocurrent in absence of a photosensitizer suggest an intrinsic bulkcharge generation mechanism. The intensity dependence of the photocurrent suggests a combination of nongeminate and alien recombination of charge carriers. The increase of the quantum yield in the presence of air is an indication that, upon photoexcitation, mobile holes are formed. By covering the multilayer assembly with a rhodamine containing monolayer, a significant increase of the quantum yield is obtained upon excitation of both the anthracene chromophore and the dye. In the case of dye excitation, the values and the field dependence of the photocurrents due to the photosensitized injection of holes from the layer of excited dye molecules into the 2A7 multilayer resemble those obtained for anthracene crystals covered by adsorbed dyes.
ADVERTISEMENT RETURN TO ISSUEPREVArticleGaussian distributions of the decay times of the singlet excited state of aromatic amines dispersed in polymer films. [Erratum to document cited in CA118(8):60625x]G. Verbeek, A. Vaes, M. Van der Auweraer, F. C. De Schryver, C. Geelen, D. Terrell, and S. De MeutterCite this: Macromolecules 1993, 26, 15, 4074Publication Date (Print):July 1, 1993Publication History Published online1 May 2002Published inissue 1 July 1993https://pubs.acs.org/doi/10.1021/ma00067a059https://doi.org/10.1021/ma00067a059research-articleACS PublicationsRequest reuse permissionsArticle Views21Altmetric-Citations1LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTGaussian distributions of the decay times of the singlet excited state of aromatic amines dispersed in polymer filmsG. Verbeek, A. Vaes, M. Van der Auweraer, F. C. De Schryver, C. Geelen, D. Terrell, and S. De MeutterCite this: Macromolecules 1993, 26, 3, 472–478Publication Date (Print):February 1, 1993Publication History Published online1 May 2002Published inissue 1 February 1993https://doi.org/10.1021/ma00055a011RIGHTS & PERMISSIONSArticle Views119Altmetric-Citations18LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (897 KB) Get e-Alerts Get e-Alerts
Using X-ray reflectivity, we have investigated the vertical ordering of multilayers of an asymmetrically substituted triphenylene derivative. A value of 1.37 nm is found for the thickness of an individual monolayer. Detailed fits for the reflectivity data have been performed. The corresponding electron density profiles suggest that very smooth, regular Y-type films are formed. The absence of clear Bragg peaks in the X-ray reflection curve and the small electron density fluctuations in the multilayer can be explained by an interdigitating packing of edge-on oriented disks in adjacent layers.
