Sensors
One of our main interests lays in designing active compounds for detection of various analytes. Our materials often exhibit a measurable change in physico-chemical properties upon exposure to detected analyte. For example, we developed an imidazolium-based [6]helicene, which can form stable films capable of changing their conductivity by a couple of orders of magnitude, depending on whether or not the surrounding atmosphere contains water and therefore act as an effective water sensor. The two enantiomers of the same molecule also showed different binding modes towards DNA and is currently studied as a potential candidate for DNA sensing. We can also use changes in fluorescence as indicators for presence of analytes. For instance, 2,6-disubstituted [6]helicenes decorated with strong amine based donors and phosphinoxide acceptors show very strong
solvatochromism in presence polar solvents, especially alcohols. Even low concentrations of alcohol in the solution can dramatically shift the fluorescence maximum wavelength and therefore also its colour.
Many physico-chemical properties can be used for sensing applications and in case of polyaromatic
materials it is mainly their absorption, fluorescence, or conductivity, to name a few. In case of helicenes, their chiral response can be also changed in interaction with chiral analytes and observed as a signal in circular dichroism spectra, polarized luminescence spectra, or in specific applications of Raman spectroscopy. We work on finding such systems with a potential of their utilization in real life applications.
Chiral plasmonics
Special place in our research of various sensors is reserved for utilization of helicenes in chiral
plasmonics. Unlike common detection methods, Surface-enhanced Raman Spectroscopy (SERS)
represents an extremely sensitive method for detection of substrates in concentrations as low as
1013M. The sensor is constructed by sorption, or chemical attachment of enantiomerically pure helicene molecule onto a nanostructured metal substrate, most often made of gold or silver. This setup allows for an interaction between the molecule of the chiral analyte and of the helicene, which in turn causes a change in the Raman response of the system.
These systems can be extensively tuned for various applications and analytes, by changing the
structure and electronic properties, by variation of the contact between the metal surface and
helicene, and also by engineering of the surface of the metal. Our goal is to be able to distinguish
between enantiomers of complex chiral compounds, especially those of biological relevance.
Chiral electrodes
Electrochemical transformations are nowadays increasingly studied, but the application of such
methods to large polyaromatic systems is still in its infancy. Our contribution to this quickly evolving field was a number of studies of electropolymerizations of helicenes bearing different functional groups. This way, it was possible to modify different electrodes with a uniform coating of helicene-based polymer and could be done either by polymerization of appended functionalities, such as thienyl groups, or on the helicene backbone itself. Our method is efficient and mild, which allows the helicene to maintain its unchanged properties – chirality is retained and the functional groups on the helicene are often well tolerated. As a result, the whole surface of the electrode can be very simply made chiral, but also responsive to different redox potentials.
Such electrodes have a largely extended application potential. Among other possibilities,
electrochemical sensing, chiral electrochemical transformations and photoelectrochemistry can be
mentioned as intriguing ways to utilize this type of materials.
Optoelectronics
The majority of polycyclic aromatic hydrocarbons (PAHs) have the potential to be utilized as active
materials in a variety of electronic devices, such as diodes, transistors or solar cells. Our research in this area is focused on design of new derivatives of helicenes and phenacenes and a study of the structure – properties relationship, as well as improving the limiting properties, such as low fluorescence quantum yield, crystal packing or charge mobilities. The main advantage of helicenes in this field is – again – their chirality. Not only can they be utilized as OFET based sensors for circularly polarized light and chiral molecules, sufficiently luminescent derivatives can also be made into OLEDs and displays capable of emitting circularly polarized light (CPL). Such devices could have a simpler design and operate at lower voltages, thus improving the energy efficiency of the display.
For this type of applications, we use a plethora of polyaromatic molecules, differing in their structure, substitution and behaviour. From pefluorinated phenacenes and helicenes and molecules with single heteroatom at different positions, to metal complexes and complex push-pull and polyhelicene systems, we try to come up with new ways to improve the current performance levels of organic-based devices.
List of projects
