Synthesis of rotaxanes based on vinylsulfonyl "click" chemistry and study of their chiroptical properties. Study of host-guest chemistry of curved PAHs

Abstract

The results presented in this doctoral thesis are divided in two different parts. The first one, focused on the development of new synthetic methodologies to afford rotaxanes and their applications, is subdivided in a general introduction and two chapters, whereas the second one consists of a single chapter in which the study of the supramolecular chemistry of polycyclic aromatic hydrocarbons (PAHs) with seven-membered rings is discussed. Firstly, in the first part, a general introduction is included with a literature review of the main advances achieved to date in the field of rotaxane synthesis and applications. Thus, the possible strategies and the numerous structural motifs and template effects employed to create rotaxane structures are displayed. Moreover, the key feature of rotaxanes for their applications as molecular machines, namely the control of the relative position of both components within this architecture, is discussed as well as the resulting applications coming from this possibility. The first chapter is entitled “Synthesis and applications of [2]rotaxanes using click Michael-type addition reactions to the vinyl sulfonyl group“ and separated in two blocks. The first one deals with the synthesis of rotaxanes, while the second one, with their disassembly. Regarding the first block, we conducted a literature review about the capping and closing reactions employed in rotaxane synthesis and a description of the Michael type addition to the vinyl sulfonyl group and its applications. Then, the experimental results obtained using, for the first time, this reaction in the synthesis of rotaxane based on π-donor/π-acceptor interactions, hydrogen bonding and pillar[5]arene macrocycles in very good yield (53-91%) are presented. Moreover, using this methodology, a lithium-templated donoracceptor rotaxane based on a pyromellitic diimide moiety and a crown ether ring (DNP38C10) has been prepared. Furthermore, this rotaxane can act as a sensor for metal cations (Li+, Sc3+ y In3+). In the second section of this chapter, an overview is presented of the coupling-and-decoupling concept (CAD) adapted to the vinyl sulfonate group and a description of rotaxanes able to be cleaved in a controlled manner, as well as molecular machines based on interlocked systems exhibiting a directional movement of their components, including molecular motors and pumps. Here, the disassembly of a rotaxane employing the vinyl sulfonate coupling-and-decoupling chemistry is demonstrated. Subsequently, we describe the application of this strategy to control the nonreversible unidirectional transportation of a macrocycle through the linear component of a rotaxane upon application of a chemical stimulus. The second chapter is entitled “An “ON/OFF” circularly polarized luminescence switch based on a rotaxane architecture”. In the introduction of this chapter, we discuss a literature study of the phenomenon of circularly polarized luminescence (CPL), the CPL emitters and switches, as well as, examples of chiral rotaxanes and chiroptical properties reported for such compounds. Then, the preparation and the operation of the first CPL switch based on a rotaxane. This molecular machine is composed by a fluorescent macrocycle and a pH-driven switching system with both a chiral and an achiral station in the thread. The CPL emission is based on a chiral information transfer from the chiral group of the axle to the luminescent macrocycle. Furthermore, depending on the position of the macrocycle, the CPL signal can be turned “on” or “off”. Finally, the second part of this doctoral thesis includes the third chapter entitled “Supramolecular chemistry of saddle-shaped heptagon-containing nanographenes”. This chapter begins with an introduction to graphene, nanographenes, their structural defects and the possible applications of molecules having such defects focusing on nanographenes with negative curvature. Furthermore, a literature review about the supramolecular chemistry of curved and planar extended PAHs is presented, discussing their self-association properties in solution, their host-guest properties and the supramolecular materials generated with such compounds. From this review, it can be concluded that nanographenes containing heptagonal rings remain unexplored in this field. In this context, within this chapter, the experimental results obtained combine the synthesis and characterisation of saddleshaped nanographenes including a heptagonal ring with the study of their self-association in solution and their ability to establish supramolecular interactions with different aromatic molecules, planar and curved, as well as electron-rich or poor π-systems. Moreover, we describe the synthesis of three amphiphilic nanographene incorporating this type of curvature with the objective of applying them in possible future applications in self-assembly of supramolecular materials.