Low-Coordinate Organopnictogens : Synthesis and Optoelectronic properties

Abstract: This thesis work is based on the development of novel organopnictogen compounds and the exploration of their potential applications in organic electronics. In particular, incorporation of phosphorus and arsenic into π-conjugated systems is known to modify the optoelectronic properties.The first chapter of this thesis is fully devoted to the development of a metal-free synthetic route that allows direct, sequential and stereoselective alkynylation of C,C-dibromophosphaalkenes. The subsequent unusual reactivity of thus synthesized C-mono and C,C-diacetylenicphosphaalkenes with terminal acetylenes afforded highly substituted 1-phoshpha-1,3-butadienes heavier analogue of all carbon 1,3-butadiene motifs. Optimization of the reaction condition favored exclusively the formation of 1-phospha-1,3-butadienes. Unveiling the unique cyclization of the 3-yne 1-phospha-1,3-butadiene gave highly substituted phosphole derivatives. Further, it has been experimentally shown that the P=C unit is essential for this rare cyclization and rearrangement to give π-conjugated phosphole derivatives.The second chapter of this thesis work deals with incorporation of P/As in the form of phosphinidene and or arsinidene units as an exocyclic substituent at the bridge of the fused rigid cyclpentadithiophenes (p-CPDT) core. Furthermore, it demonstrates how this chemical modification at the bridgehead position selectively lowers the LUMO level. At a later stage, substitutions at α and α` positions of the central CPDT core was used to modify the HOMO level without further affecting the LUMO level. We also performed DFT calculations on these phosphinide/arsinidene p-CPDT derivatives to theoretical evaluate the impact of P and or As incorporation. The phosphinidene/arsinidene p-CPDT derivatives were fully characterized using electrochemical and optical spectroscopic techniques including transient absorption spectroscopy. Additionally, the arsinidene-p-CPDT were electrochemically polymerized, and the resultant polymer film was characterized by means of SEM and EDX.The last chapter of this research work is dealing with the exploration and functionalization of open-ended small fragments of fullerene-C60 such as sumanene and truxene. Functionalisation of these motifs was achieved via the introduction of pnictogens (P/As), either in the form of phosphinidene/arsinidene or as heteroles. The optoelectronic spectra of the unprecedented pnictinidenotruxene exhibited significantly redshift absorption and three fully reversible reduction events upon electrochemical reduction.