Graphene Oxide‐BODIPY Conjugates as Highly Fluorescent Materials

Abstract Covalent functionalization of graphene oxide (GO) with boron dipyrromethenes (BODIPYs) was achieved through a facile synthesis, affording two different GO‐BODIPY conjugates where the main difference lies in the nature of the spacer and the type of bonds between the two components. The use of a long but flexible spacer afforded strong electronic GO‐BODIPY interactions in the ground state. This drastically altered the light absorption of the BODIPY structure and impeded its selective excitation. In contrast, the utilisation of a short, but rigid spacer based on boronic esters resulted in a perpendicular geometry of the phenyl boronic acid BODIPY (PBA‐BODIPY) with respect to the GO plane, which enables only minor electronic GO‐BODIPY interactions in the ground state. In this case, selective excitation of PBA‐BODIPY was easily achieved, allowing to investigate the excited state interactions. A quantitative ultrafast energy transfer from PBA‐BODIPY to GO was observed. Furthermore, due to the reversible dynamic nature of the covalent GO‐PBA‐BODIPY linkage, some PBA‐BODIPY is free in solution and, hence, not quenched from GO. This resulted in a weak, but detectable fluorescence from the PBA‐BODIPY that will allow to exploit GO‐PBA‐BODIPY for slow release and imaging purposes.