Control and quantification of interchromophoric coupling in single-molecule defined shape-persistent oligomers

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We propose to synthesize well-defined molecular model systems to read out electronically coupled excited states between pi-conjugated oligomers by spectroscopy and to characterize this coupling in combination with quantum chemical calculations. This kind of excited state coupling plays a particularly important role regarding the optoelectronic properties of conjugated polymer based devices, but is difficult to control and to quantify in such disordered materials. Novel molecular mesoscopic material systems will be exploited as model systems to develop design rules and to correctly interpret observables of the photoluminescence (PL), e.g. the PL lifetime, PL quantum yield and wavelength of emission, in terms of several morphological parameters, e.g. distance, number and length of participating pi-conjugated molecular units. Independent from optical spectroscopy, the distance between the oligomers will be determined by means of STM and NMR experiments. Intramolecularization of intermolecular spectroscopic properties will be achieved by novel material systems which exploit a control of (i) the intramolecular pi-conjugated oligomer-oligomer distance by attachment to carefully designed molecular clamps; (ii) the pi-conjugated oligomer length; and (iii) the number of participating pi-conjugated oligomers. Since tiny variations in distance between these pi-conjugated oligomers will result in different spectroscopic properties, single-molecule spectroscopy will be employed to unravel any structural heterogeneity within these model systems. The results will be used specifically to exploit the PL as a reporter on tiny structural, i.e. interchromophoric distance variations on sub-Ångström length scales, within a model system. This coupling cannot be described sufficiently in the conventional terms of either H-aggregation or excimer formation. Therefore it is mandatory to compare the experimental results with quantum chemical calculations in order to obtain a fundamental understanding of the intermolecular coupling mechanism of the pi-conjugated oligomers.