Abstract
We report the synthesis, characterization, and the thermotropic and photoluminescence properties of dialkoxyterphenyls with (T12-CN and T12-2CN) and without (T12) nitrile groups. These terphenyls were prepared through the Suzuki-Miyaura cross-coupling reaction using a palladium-based catalyst. The products obtained were analyzed as powders or after being drop-casted or spin-coated on glass. Nuclear Magnetic Resonance (1H NMR) and Fourier Transform Infrared (FTIR) spectroscopy techniques confirmed the structure and purity of the synthesized terphenyls. The mesomorphic behavior was studied by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X-ray diffraction (XRD). T12 developed various mesophases, whereas T12-CN and T12-2CN displayed one single mesophase of low order over a wide temperature range. The films topology was studied by AFM and the optical properties were determined by ultraviolet-visible (UV-Vis) spectroscopy and spectrofluorometry. Higher roughness was found for the films prepared with the asymmetric terphenyl (T12-CN). The photoluminescence (PL) spectrum obtained for the asymmetric terphenyl (T12-CN) exhibited the expected characteristics with an emission band centered at 381 nm and an overtone around 760 nm.
Highlights
In the recent years, π-conjugated organic molecules have been the subject of increasing attention due to their unique electrical and optical properties, which make them suitable active materials for photovoltaic cells [1], photodiodes [2, 3], and molecular sensors [4,5,6,7], among other optoelectronic devices [8,9,10,11]
Characterization, and the thermotropic and photoluminescence properties of dialkoxyterphenyls with (T12-CN and T12-2CN) and without (T12) nitrile groups
The mesomorphic behavior was studied by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X-ray diffraction (XRD)
Summary
Π-conjugated organic molecules have been the subject of increasing attention due to their unique electrical and optical properties, which make them suitable active materials for photovoltaic cells [1], photodiodes [2, 3], and molecular sensors [4,5,6,7], among other optoelectronic devices [8,9,10,11]. The oligo-p-terphenylenes are of particular interest because the smallest (terphenyl, quaterphenyl, and quinquephenyl) are able to radiate a high energy light in the blue region of the spectrum and display a rich thermotropic polymorphism These oligomers are commonly modified with flexible chains [12, 13] and other groups [14, 15]. Such disruption increases their entropy and improves the number of conformations that can take place to effectively decrease their melting point and improve their solubility Another outstanding aspect of the oligo-p-phenylenes is their ability to form flexible and resistant films by spin coating and dip coating methods which can be used as active layers in organic light-emitting diodes (OLEDs) of relatively large area [16]. Thin films were deposited over a glass substrate in order to evaluate their photoluminescence for potential applications in organic semiconductor devices
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