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Title: Synthesis and characterisation of novel star-shaped oligoluorenes for organic semiconductor lasers
Author: Pen~a, Clara Orofino
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 2013
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The vast efforts dedicated to the improvement of light emitting semiconductors for light emitting diodes (LEDs) led to the leap of these materials into lasing applications. Organic semiconductor lasers (OSLs) quickly became an excellent complement to their inorganic counterparts as compact, low cost visible lasers that can even be produced on flexible substrates. The simple processability of organic semiconductors, coupled with excellent optical properties such as strong absorbance and emission profiles, high photoluminescence quantum yields and especially the possibility to tune such properties in a simple manner through chemical or physical modifications has enabled the use of OSLs in a wide variety of applications such as spectroscopical light sources, visible light communications or chemical sensors. Monodisperse oligomers allow perfect chemical control of the optoelectronic properties of the materials, which lead to high-performance reproducible lasers. Furthermore, the increase in dimensionality of these oligomers through the introduction of a central core to obtain star-shaped materials provides a greater degree of anisotropy of their properties as well as enhanced control of the morphology in the condensed state. Star-shaped oligomeric materials have featured in OSLs with excellent performance and research in this area is becoming widespread. Chapter 1 provides an overview of the properties of organic semiconductor light emitting materials and the basic principles of organic semiconductor lasers, including the applications and the ultimate goal of this class of device. A very short overview of the principles behind OLED operation is also described. Chapter 2 introduces developments in oligofluorenes and the concept of star-shaped oligomeric materials. The synthesis and properties of two families of such star-shaped oligofluorene truxene compounds with butyl and octyl chains (Tn) are introduced and compared with the already published Tn (hexyl) series. The impact of the length of the alkyl chains of these materials on their synthesis, thermal and photophysical properties is discussed and this comparative study is extended to an explosive sensing study based on OSL. The importance of the position of an acceptor BT unit within the oligofluorene arms of a star-shaped quaterfluorene truxene molecule is discussed in Chapter 3. The structural symmetry around the BT unit leads to three distinctive locations with important implications on the photophysical properties. Chapter 4 describes the attempt to avoid aggregation previously observed in a family of materials with 9,9-dihexyloligofluorene arms and DPP cores through the enlargement of the solubilising alkyl chains (octyl). The importance of the excitation wavelength in the photophysical properties of this class of materials is also assessed. Chapter 5 presents the synthesis and characterisation of two star-shaped compounds with four oligofluorene arms and a tetraphenylethene core. The materials are efficient emitters in the aggregated state, but not in solution, due to their aggregation induced enhanced emission (AIEE) properties. Furthermore, their lasing capabilities and the effect of pressure on their emission properties is discussed, indicating that they could be used in a new generation of pressure sensor devices. The importance of the substitution pattern in T- and Y-shaped materials with BODIPY cores and oligofluorene arms is discussed in Chapter 6. The variation of the location of two of the arms within the core has a dramatic effect on the optical properties of the materials, which are promising for lasing applications such as visible light communications. The experimental procedures for chapters 2-6 are presented in Chapter 7.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available