Novel Photoresponsive Organic Materials and Molecular Devices 

The development of functional organic materials is a rapidly growing area of science, which promises to replace traditionally used materials with cheaper and better-performing new ones, and often brings about new applications that humankind never considered before. The „bottom-up“ approach we pursue in my research group starts from a thourough design of a molecule possessing a desired property, and then transferring it into a bulk material or device. The substantial part of our research efforts is directed towards using light as a way to control the material's behavior. Such materials may find use in nanoscale electronics, photonics, molecular computing, sensors, biological imaging and in a variety of other fields. The detailed studies will also enhance our understanding of the fundamental principles behind their functioning. This multidisciplinary research program combines contemporary and traditional areas of physical-organic and synthetic organic chemistry, theoretical and computational chemistry, and macromolecular chemistry. Some of the current projects are outlined below.

Conjugatedpolymers representa unique class of organic materials which can be easily tailored or modified for a desired application. We are working on the design of a new class of conjugated polymer based light-controlled materials. Their electrical, photophysical and optical properties can be switched reversibly by applying external light. In order to achieve this goal, we synthesize polymers that incorporate photochromic units into the conjugated chain. In the photochromic units, a reversible photochemical interconversion betweenp-conjugated and unconjugated forms can be performed by an appropriate choice of irradiation wavelengths. This will lead to an efficient control of the polymer conjugation length - an important parameter determining most of the properties of conjugated polymers. Our studies are directed towards making these materials efficiently work and be long-lasting. In addition, this class of polymers can be chemically modified for photochemical switching via two-photon absorption. The resulting materials can find use in the fabrication of complex 3D microelectronic and photonic devices.

Another direction of our research involves the development of a novel solid-state sensing platform based on self-assembly of the specially designed molecular sensors. In the core of this approach is the possibility to control excitation energy transfer in rigid conjugated sensor molecules by binding of an analyte. When no analyte is present, the irradiation of the sensor monolayer results in the fluorescence emission from the terminal lower band gap groups as a result of an excitation energy migration. Docking of an analyte to the sensor’s receptor element results in the quenching and diminishing of this emission, with a simultaneous appearance of a different color emission from the conjugated backbone. We are conducting studies towards deeper understanding of the photophysics of energy transfer, which will allow us to successfully implement this strategy into practical sensing devices. This will enable building of robust solid sensors for detecting of various hard-to-detect analytes, including in vivo biosensing.

Similar methodology based on self-assembled monolayers will be used for creating highly efficient organic photovoltaic devices. It utilizes a new “bottom up” approach based on the stepwise self-assembly of two types of molecular building blocks with rigid rod-like geometry and opposite electronic demands. The correct assembly of the electronically opposite building blocks into a photovoltaic molecule occurs by utilizing the supramolecular connectors attached to each block, which are complementary to each other. This approach is expected to yield a highly ordered and well-organized framework which incorporates a heterojunction between n- and p-sublayers on the intramolecular level. In addition, this supramolecular design facilitates the fabrication of a variety of photovoltaic devices based on a few building blocks, thus enabling a rapid combinatorial screening to find the most efficient structures.

Our research interests also extend into the area of design of fluorescent and photoreactive biomarkers. In one of the projects, we are working on the targeted delivery into the brain and controlled release of amyloid aggregates disruptors. Despite the ongoing scientific debates whether the aggregated Amyloid-b (Ab) plaques in the brain are a cause or merely a consequence of Alzheimer’s disease, significant body of evidences point out on high neurotoxicity of aggregated Ab, which is likely to be directly involved into the pathogenesis of the disease. Thus, disrupting the amyloid aggregates or preventing further aggregation may have a positive therapeutic effect. We are working on the design of “caged” amyloid disruptors, which are capable of entering the brain in the inactive form after an intravenous injection, and selectively binding to amyloid deposits. The special molecular design will allow subsequent release of an active form of the disruptor triggered by two-photon absorption in the far-red region.

We are working on a new fundamental approach to increase and control selectivity of photochemical processes using liquid crystalline materials. The liquid crystalline medium is employed to impose a unidirectional orientation on an array of dissolved guest molecules. Subsequent cooling of this system below the melting temperature of the liquid crystalline host results in a solid material where all the guest molecules are uniformly oriented in a preferential direction. Polarized light will be used to selectively excite a particular electronic transition in the guest molecules, which is expected to lead to an increased selectivity of their photochemical transformations. Moreover, the photochemical course can be easily manipulated by changing the angle between the polarization plane of the incident light and the liquid crystal director, due to the ability to selectively excite the electronic transitions with differently oriented transition dipole moments. This method may become a powerful tool to study mechanisms of photochemical reactions, as well as a way to control photochemical reactivity. In addition, these unique anisotropic solid materials possess interesting electronic, optical and mechanical properties, which are being investigated in our group.