# Synthesis, Characterization, and Self-Assembly of a Tetrathiafulvalene (TTF)-Triglycyl Derivative
## 1 Introduction  
Oligonucleotide conjugates carrying aromatic systems are important tools for a large number of applications due to their enhanced hybridization properties and their special fluorescence and chemical properties coming from the aromatic moieties [1; 2; 3; 4; 5; 6]. Recently, tetrathiafulvalene (TTF) derivatives have been incorporated in oligonucleotides demonstrating the fluorescence-quenching properties of the DNA-TTF conjugates upon hybridization [7], the preservation of the electrochemical properties of TTF [8], an enhanced affinity to complementary sequences [9], and compatibility with the RNA interference mechanism for gene inhibition [10]. In the field of materials chemistry, TTF and its derivatives constitute electron donors that can form charge-transfer (CT) complexes and have been widely studied for the development of electrically conducting materials [11; 12]. TTF moiety can be consecutively oxidized to the radical cation TTF\({}^{+}\) and dication TTF\({}^{2+}\) by either electrochemical or chemical processes. Due to the reversibility of these transformations [13], TTF has become a general building block for the fabrication of switchable functional materials [14; 15; 16; 17], including supramolecular self-assembled nanostructures [18; 19; 20; 21]. The interesting properties of the TTF-oligonucleotides prompted us to synthesize a TTF derivative carrying a biodegradable triglycerides peptide linker between the oligonucleotide and the TTF molecule. This simple peptide sequence has been demonstrated to be hydrolyzed by cathepsin B present in endosomes [22]. During the preparation of the mentioned TTF derivative we accidentally observed the formation of gels in some solvents. In general, gels have received great attention during the last decade [23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34] due to their exceptional hierarchical architectures and potential applications in many important areas such as biomedicine, health care, and catalysis, among others [35; 36; 37; 38; 39; 40; 41; 42; 43; 44; 45]. Chemical gels are based on covalent bonds, usually cross-linked polymers [46; 47; 48], whereas physical gels (also called supramolecular gels) are normally fabricated using low-molecular-weight (LMW) molecules that self-assembly via non-covalent interactions. For this reason, supramolecular gels usually show reversible stimuli-responsive _gel_-to-_sol_ transitions [23; 24]. Systems based on both covalent and non-covalent interactions are also known [49]. Typically, the entanglement of 1D nanofibers of gelator molecules generates a 3D-network with the solvent molecules trapped into the interstices by capillary forces. This provides a solid-like appearance and viscoelastic features to physical gels [50; 51; 52; 53]. Within this context, [PERSON] and co-workers reported in 1994 [54] the first TTF-based LMW gelator bearing bis-arborol units, which was used to fabricate a self-assembling \"molecular\" nanowire [55]. Since then, a large number of electroactive TTF-based LMW gelators and their gels have been described in the literature [56]. In general, the rational design behind these examples involves the connection of the TTF unit with groups capable of H-bonding, such as urea [57] or amide groups [58; 59; 60; 61; 62; 63], to form extended structures. The incorporation of other molecular building blocks commonly used to form physical gels [64; 65; 66; 67] or the use of metal-organic interactions [68; 69; 70] have also been employed to form TTF-based gels. Moreover, the inclusion of hydrophobic aliphatic chains is also employed to facilitate van der Waals interactions and stabilize the supramolecular aggregates [58; 59; 70; 71]. If formation of CT complexes takes place, the TTF unit will bear positive charge, which can alter the interaction of neighboring TTF units and influence the intermolecular interactions arising from other groups involved in the self-assembly process. Indeed, the above-mentioned studies have confirmed the possibility of tuning the gel formation by CT interaction and oxidation.