To path indicator Subpages of “FOR 5781“ To navigation To quick access To footer with other services
To content
FOR 5781 -> f:format.stripTags()
Department of Chemistry and Chemical Biology
Studenten im Sommer auf dem Campus Nord, rote Zahnräder im Hintergrund © Roland Baege​/​TU Dortmund

Summary

Exploring structure-property relationships of smart materials is of great importance for the development of efficient and sustainable future technologies. In the area of photonic materials, stimulus-responsive (SR) systems particularly stand out because their photophysical properties, including emission wavelengths, lifetimes, quantum yields, circular dichroism (CD), or energy transfer (EnT) rates, can be varied by an external influence. Various forms of chemical reactivity to affect a photophysical response, such as pH value changes, ion binding, oxidation/reduction or solvent association, have been studied in great detail and exploited for biological imaging, photodynamic therapy and in sensing applications.

In contrast, physical stimuli and field effects by applying pressure, stress, magnetic and electric fields to phosphorescent coordination complexes are much less explored, which explains the lack of generalizable structure-property schemes for photonic SR. This is surprising, given the variety of coordination geometries that allow for different structural distortions to provide an optical response to an external physical stimulus. Furthermore, the diversity of excited state natures (MLCT, LMCT, LC, MC, ILCT, LLCT) can be tuned by the ligand spheres, of which the different electron density distributions are also prone to very diverse SR photonic effects. Similarly, environmental influences on SR photonic behaviour of transition metal complexes have not been investigated in detail yet, although this knowledge is fundamental for application scenarios – and the combination of various physical stimuli is literally unknown. Clearly, the target-oriented design and application of such complexes for implementation in advanced photonic technologies is currently impossible due to missing general structure-property relationships.

This intellectual knowledge gap is the main motivation for the formation of the interdisciplinary research unit STIL-COCOs, which represents a collaborative network of 9 groups with complementary expertise to establish a new class of smart photonic materials and to lay the foundation for implementation in technological platforms. Some members of this Research Unit have individually developed molecular systems displaying photonic stimulus-responsiveness (Steffen, Strassert, Heinze), while others have developed spectroscopic (Henke, Bauer, Richert, Vöhringer) and theoretical methods (Doltsinis, Bannwarth) that are vital for the planned research of this network and have initiated first collaborations already on this topic, which are described below.

Objectives. The Research Unit STIL-COCOs will establish luminescent SR metal complexes for application in photonic key technologies, such as advanced devices, multi-parameter sensing, anticounter-feiting, data storage and quantum IT. To reach this aim, the following objectives guide the work programme of the 2 funding periods:

The figure is divided vertically into six sections. The first section shows the prototypical coordination compounds with their d-electron configuration and the states that typically determine the emission behavior: - A linear copper-one complex with a d10 configuration and emission from LLCT or MLCT states; - A square planar platinum-two complex with a d8 configuration and emission from LC or MLCT or MMLCT states - An octahedral chromium-three complex with a d3 configuration and emission from MC or LC states The second section specifies the aggregate states in which the compounds are investigated, namely in solution, in polymer films, in the solid state, and intercalated in metal-organic framework compounds, or MOFs for short. In the third section, a vertical arrow connects the coordination compounds and aggregate states above with the term “stimulus response,” that’s to say, the response of the system to an external influence. To the left and right of the arrow are the corresponding influences being investigated by the research group, namely pressure, tensile and shear forces, grinding, and electric and magnetic fields. The fourth section lists three different aspects of stimulus response: 1) changes in experimentally accessible quantities such as emission wavelength, quantum yield, lifetime of the excited state, or dissymmetry factor g-lum; 2) qualitative properties of these changes, namely the selectivity, sensitivity, and reversibility of the stimulus response; 3) causes at the molecular level that may be responsible for the stimulus response, i.e. structural changes, the occurrence or absence of intermolecular interactions, changes in the environment in the crystalline solid, influences on the electronic ground state or excited state, and the introduction of chirality. In the fifth section, an arrow connects these three aspects with the term “structure-property relationship,” thus naming one of the core objectives of the research project: the establishment of such relationships in order to be able to create molecules in the future that exhibit the desired stimulus responsiveness. The last section lists areas of technological application for which the findings could be significant, such as responsive OLEDs, chirality switches, entangled photon sources, and more. © Andreas Steffen​/​TU Dortmund
  1. Evaluation of modes of SR action in dependence of complex geometry. The 3-dimensional structure of the complexes is decisive for potential structural distortion and intermolecular interactions, and has an enormous influence on the excited state properties. Thus, linear, square-planar and octahedral coordination geometries as the most fundamental ones will be exposed
  2. Control SR in dependence of excited state nature. Employing CuI, PtII and CrIII complexes in their d10, d8 and d3 electron configuration, respectively, all classical excited state characters will be covered, including MC or IL, ML/LMCT, LLCT and (MM)LCT states, representing very diverse electron density distributions and excited state lifetimes, for which the various physical stimuli will give very different response functions.
  3. Exploiting application-relevant environment dependence of SR. The photophysical SR behaviour will be investigated in application-relevant polar and non-polar environments, including solution, films of (non-)polar organic matrix materials, MOFs and crystalline and amorphous solid state for advanced control.
  4. Demonstrate applicability and establish a multivariant space of photonic SR. Proof-of-concept device application and coupling of the singular systems to provide access to an unprecedented multidimensional array of properties for visionary future applications.

The 1st funding period is expected to provide a comprehensive stimulus-structure-photonic response scheme and gain control over the modes of action for application quality. The focus is on the photophysical SR behaviour of model systems by applying i) pressure, ii) stress, iii) shear force, iv) grinding, v) magnetic and vi) electric field, with evaluation of the

  1. Read-out – emission wavelengths, quantum yields, lifetimes, radiative and non-radiative decay rates and chiroptical properties
  2. Quality – selectivity, sensitivity, reversibility of the response
  3. Origin – structural changes of ground state and/or excited state, intermolecular and environment interactions, rigidity of environment and changes of the excited state nature.