Tetraphenylethylene luminogens : design, synthesis and applications

Abstract

Design and synthesis of luminescent organic solids with different color emission have been continuously attracting the scientific community for various optoelectronic applications. However, most of the organic solids are non-emissive in the solid state due to the obstacle called aggregation caused quenching (ACQ). A great deal of efforts has been done to minimize the aggregate formation but have ended up with limited success. The formation of aggregates at high concentration or in solid state is an inherent phenomenon and difficult to prevent it. Tang et al. in 2001 utilized the aggregation phenomenon and developed an anti ACQ material which shows emission in the aggregated state and termed this concept as aggregation induced emission (AIE). The AIE materials are highly fluorescent in the solid state and work on the principle of restricted intramolecular rotations. Generally, the propeller shape molecule exhibits AIE behavior, and based on this concept various AIE active compounds have been developed. The tetraphenylethylene (TPE) moiety has propeller shape molecular structure and exhibits AIE behavior. The TPE can be functionalized at various positions by changing the synthetic methodology. Owing to these properties TPE serves as an important luminogen in the field of solid state emission and being utilized in various applications such as organic light emitting diodes (OLEDs), metal ion sensors, mechano-sensors, supramolecular assemblies and in-vivo as well as in-vitro bio-imaging. The fascinating properties of TPE derivatives inspired us to develop new TPE based luminogens which would be applicable in OLEDs and emerging area of mechano-sensors. We have coupled TPE to various chromophores such as phenanthroimidazole, pyrenoimidazole, benzothiadiazole and pyrazabole with varying degree of electronic structure and acceptor strength and further studied their photophysical, AIE and mechanochromic properties.The main objectives of the present study are;  To design and synthesize new TPE based AIE-active luminogens which can show different colored emission.  To study the structure property relationship of the new TPE based luminogens.  To explore the mechanochromic applications of the new TPE based AIE luminogens.  To investigate mechanistic understanding of the AIE and mechanochromic effect.