Aggregated Excimer Formation through Hydrogen Bonding in a Pyrene–Urea Derivative
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We examined intermolecular hydrogen-bonding interactions of pyrene derivatives bearing a urea unit, referred to as 1PUP (one pyrenyl group) and 1DPU (two pyrenyl groups). 1DPU showed a new emission band around 530 nm along with a locally excited emission (LE) attributed to the pyrene moiety, even at 10<sup>−7</sup> M, in contrast to 1PUP, which only had an LE, indicating that the symmetrical configuration allowed stable stacking of 1DPU. Time-resolved emission spectroscopy revealed that the intensity of the new band increased relative to that of the LE with the concentration of 1DPU. Furthermore, addition of tetrabutylammonium acetate (TBAAc) resulted in the disappearance of the new band, due to the formation of hydrogen bonds with 1DPU. These results indicate that the new band may originate from intermolecular hydrogen-bonding interactions between 1DPU molecules through the urea unit, even at very low concentrations, and can be attributed to an excimer emission. This implies that hydrogen bond formation by the urea units of 1DPU favors a conformation that results in the formation of the excimer in the absence of anions, and the strength of the hydrogen-bonding interaction between 1DPU molecules is weaker than the interaction between a 1DPU molecule and an anion.
- Bulletin of the Chemical Society of Japan
Bulletin of the Chemical Society of Japan 88(8), 1100-1104, 2015
The Chemical Society of Japan