Synthesis and Photophysical Properties of Pyrrole/Polycyclic Aromatic Units Hybrid Fluorophores

Abstract

A series of pyrrole/polycyclic aromatic unit hybrid fluorophores was developed by a two-stage synthetic strategy. Their central aryl-substituted pyrrole cores were constructed by a Paal-Knorr pyrrole synthesis reaction. The reaction conditions and mechanism are also discussed in detail. End-capping triflate onto the central pyrrole core enables the core to incorporate various polycyclic aromatic units. The Buchwald-Hartwig amination reaction and the Suzuki-Miyaura cross-coupling reaction were adopted to incorporate the triflate end-capping pyrrole with N-phenylnaphthalen-1-amine and various polycyclic aromatic units to form the hybrid fluorophores. The photophysical properties and thermal properties of the fluorophores were characterized. Most of the pyrrole fluorophores emitted blue light and exhibited high quantum efficiency. The fluorescence properties of these pyrrole fluorophores were induced by manipulating the surrounding polycyclic aromatic units. When the central pyrrole core was incorporated with amino or naphthalene moieties, the fluorescence efficiency and thermal stability of fluorophores 1 and 2 were low (phi(f) < 0.35, T(g) <140 degrees C). Rigid and highly fluorescent moieties (such as pyrenyl, 9,9-dimethylfluorenyl, 9,9-diphenylfluorenyl, and spirofluorenyl groups) were grafted onto the pyrrole. Fluorophores 3-6 had high fluorescence efficiency (phi(f) > 0.99) and stable glassy morphology (the T(g) value of the fluorophore 6 was as high as 220 degrees C). Results of this study demonstrate that the sterically induced fluorescence of crowded pyrrole and the fluorescent polycyclic aromatic units significantly affect the emission properties of the hybrid fluorophores.