Concerning the cyclic bridged oligophenylenes, the conditions of synthesis and purification have been optimized. Thus, seven cyclic bridged oligophenylenes, based on fluorene or carbazole, having different size (4 or 5 units) and various alkyl chain length (from ethyl to hexyl), have been synthesized and isolated. Some linear analogues were also obtained, for comparison purpose.
Their physico-chemical properties have been determined by electrochemical studies (determination of the redox properties, electrochemical gap, HOMO/LUMO energy levels), NMR studies (determination of the conformation and the dynamic properties in solution). Their structural properties at the solid state have been determined by X-Ray diffraction (supramolecular arrangement) and STM. The photophysical properties have been determined through UV-visible absorption, fluorescence and phosphorescence measurements (stationary and time-resolved studies). Theoretical calculations were also carried out and correlated to the experimental data. For one example (obtained with the highest yield), the mobility of the charge carriers was determined using OFET.
Finally a precise structure properties relationship study has been done, the principal elements of which are as follows:
- Compared to their linear analogues, cyclic bridged oligophenylenes display a better control of the emission of the ring in the solid state, which augurs well for the future development of material,
- Compared to CPPs, the presence of a bridge induced different geometries both at the fundamental and excited states and hence different structural and electronic properties,
- Compared to one another, the nature of the bridge (carbon atom for fluorene vs nitrogen atom for carbazole) influence both the structural and the electrochemical properties and only slightly the spectroscopic properties,
- Compared to one another, the length of the alkyl chain linked to the bridge has an unexpected influence on the structural and electronic properties of the 4-cyclofluorenes, whereas the 5-cyclofluorenes and the 4-cyclocarboles are not influenced by this parameter, showing thus the specificity of the 4-cyclofluorenes family,
- Compared to one another, the nanoring size (4 or 5 units) influence both the dynamic behavior in solution and the structural arrangement at the solid state since the largest nanorings display a smaller strain energy than the smallest. Also, the emission properties are totally different.
The synthesis of the 4-cyclofluorene bearing ethyl chains and the specificity of the properties of this molecule compared to both linear analogue and 4-cyclofluorene bearing other alkyl chains have been published (L. Sicard, O. Jeannin, J. Rault-Berthelot, C. Quinton, C. Poriel, ChemPlusChem 2018, 83, 874) and presented during a congress (The Third International Symposium on the Synthesis and Application of Curved Organic π-Molecules & Materials, Oxford UK, 5-7 September 2018). The other results will be the object of future publications and presentations during future congresses (for example, the synthesis and the properties of cyclocarbazoles will be presented during the 9th International Conference on Molecular Electronics, Paris, 17-20th December 2018).
