Organic−Organic Heteroepitaxy of Red-, Green-, and Blue-Emitting Nanofibers

Abstract

Self-assembly processes and organic-organic heteroepitaxy are powerful techniques to obtain highly ordered molecular aggregates. Here we demonstrate that combining both methods allows not only to fabricate highly crystalline and uniaxially oriented self-assembled nanofibers but also to tune their polarized emission. We show that submonolayer coverage of sexithiophene on top of para-sexiphenyl nanofibers is sufficient to change their emission color from blue to green. Triband emission in the red, green, and blue is generated in nanofibers with thicker sexithiophene coverage, where layers of co-oriented crystals are separated by green-emitting molecular sheets.

Photophysics and Photonics of Heteroepitaxial Organic Nanofibers

“…In particular, optical emission dipoles of p-6P and 6T are found to be parallel over domains as large in area as ~1 cm 2 . These optical properties support the results X-ray diffraction studies, which determine the exact epitaxial relationships between the 6T/p-6P crystal phases and muscovite mica substrate (Simbrunner et al, 2010). Despite the potential exhibited by 6T/p-6P heteroepitaxial fibers on oriented muscovite mica for broadband laser operation, at the time this review is being written no evidence of 6T lasing action in such nanostructures or in other epitaxial thin films has been reported yet.…”

“…We resort to a growth chamber equipped with two hot-wall epitaxy reactors for serial deposition of p-6P and 6T. The substrate is first exposed to the reactor with the p-6P source and than transferred to the 6T reactor; details can be found in (Simbrunner, 2010). When 6T is directly grown on muscovite, short nanofibers with red-orange fluorescence are yielded with several orientations, whereas 6T deposition on a template of p-6T nanofibers results in 6T/p-6P bilayer fibers which maintain the fiber template's orientation, with no 6T material being deposited in between adjacent p-6P fibers.…”

“…These nanofibers exhibit excellent photonic and optoelectronic properties: high blue photoluminescence efficiency (Stampfl et al, 1995), high in-fiber carrier mobility (Birendra-Singh et al, 2006;Kjelstrup-Hansen et al, 2006), luminescence guidance (Balzer et al, 2003), in-fiber amplification of spontaneous emission with large gain factors Cordella et al, 2007), and optically-induced laser action (Quochi et al, 2004(Quochi et al, , 2005(Quochi et al, , 2008. Very recently, organic-organic heteroepitaxy of mixed p-6P/alpha-sexithiophene (6T) nanofibers with highly polarized blue, green and red emission has been successfully demonstrated (Simbrunner et al, 2010), further broadening the range of potential applications of organic epitaxial nanofibers in photonics and optoelectronics. In this paper, we will review the optical and photonic properties of p-6P and mixed 6T/ p-6P nanofibers epitaxially grown on oriented muscovite mica by hot-wall epitaxy and organic molecular beam epitaxy.…”

Epitaxial growth of sexithiophene on mica surfaces

“…During the last years, the self-assembly of small building blocks such as atoms, 1,2 molecules, [3][4][5][6] and nanoparticles 7,8 into macroscopic structures has been intensively studied and recognized as a key technology in the fields of chemistry, biology, physics, and materials science. 7 In the broad spectrum of available material systems, the epitaxial growth of molecular assemblies on various substrates has been thoroughly investigated and identified as a promising basis for numerous device applications in the field of organic electronics.…”

“…In this context, the growth of rodlike organic molecules on muscovite mica substrates has been extensively studied [9][10][11][12][13][14] and, in particular, phenylenes have been recognized as key materials for a large number of optical applications, e.g., lasing and wave guiding, 15 due to their advantageous ability to form highly parallel organic nanofibers. To broaden the spectrum of optical applications the phenylene oligomers should be substituted by other rodlike molecules, e.g., acenes or thiophenes, 3,13 which presupposes a detailed knowledge concerning epitaxial growth.…”