π-conjugated organic systems have remarkable properties which have applications within several scientific fields. Two of these fields are fluorescence spectroscopy and molecular electronics which are the focus of this dissertation. For exploitation of π-conjugated organic molecules in these fields the design must be well planned and understood.
The chemical design of a chromophore determines its photophysical properties where a thorough understanding is necessary in order to develop or fine tune probes for specific applications. Triangulenium dyes are a family of stable planar carbenium systems with remarkable fluorescent properties. The family covers several branches of dyes with different optical properties which are easily tuneable from its synthetic routes. Many derivatives have already been reported in literature with functionalization on either the core structure or its sidechains yielding different properties in order to obtain application in many disciplines including photo physics and biochemistry.
In this PhD project triangulenium dyes were modified for a combined usage within both molecular electronics and as fluorescent probes. A helicene branch derived from the triangulenium core structure has in the same manner been designed and synthesized for usage in both fields.
In the first project the symmetrical triazatriangulenium (TATA+) was modified on its side chains with functional groups to obtain both a stronger binding to Au but also to tune its optical properties in interesting ways. The TATA+ derivative is the most stable carbenium system in the triangulenium family and also the most difficult to synthesize and functionalize. First the development of the synthetic procedures for these molecules were in focus, then an investigation of its new optical properties upon exposing it to protonating or deprotonating environments. Subsequently an application in molecular electronics was in focus. It has been shown that triangulenium dyes can be functionalized on its center carbon atom by nucleophiles. Such attachment of a molecular wire will create a perfect perpendicular angle between the wire and a given substrate. It has also been shown that triazatriangulenium ions form very well ordered self-assembled monolayers on Au. Combining these two findings gives advantageous content of a device based on molecular electronics. This platform approach was the last focus of the first project presented herein.
In the second project a helical family of π-conjugated molecules was functionalized on specific positions on the core structure to enable attachment of anchoring groups for break-junction measurements yielding a specific path for the current to pass through the helicenes. With this specific current path, a chiral-induced spin selectivity phenomenon can be studied using these helicenes. Two different lengths of helicenes were in focus with two very different current routes through the molecules. In the same project the helicene family was functionalized on the same specific positions in order to tune their optical properties and applications as fluorescent probes. Attaching different groups of different chemical properties to a core structure of a chromophore will tune its photo physical properties. Both [4], [5] and [6]helicenes were modified.
In the last project presented in this thesis a triangulenium molecule was altered to have a photophysical response to redox changes. Maintaining a balanced redox state is essential to cell survival and monitoring
any redox related changes within biological samples are key to detecting diseases and understanding its mechanism. By combining a redox response unit and a fluorescent azaoxatriangulenium (ADOTA+) dye a probe for monitoring redox related changes was developed and investigated in solution and in biological media.