Issue 16, 2016

The development of aryl-substituted 2-phenylimidazo[1,2-a]pyridines (PIP) with various colors of excited-state intramolecular proton transfer (ESIPT) luminescence in the solid state

Abstract

A series of solid-state luminescent dyes based on 2-phenylimidazo[1,2-a]pyridine (PIP) displaying a wide range of emitting colors from blue to red have been developed. Whereas 2′-methoxy PIP (2′MeOPIP, 10) shows blue luminescence, 2′-hydroxy PIP (HPIP, 1) exhibits emission with large Stokes shift at around 500 nm that is known as the excited-state intramolecular proton transfer (ESIPT) luminescence, which can be tuned from blue-green to red by simply introducing aryl group(s) into HPIP through Pd-catalyzed cross coupling reactions. It is shown that the energy of ESIPT luminescence decreases as the electron-withdrawing nature of the para-substituent on the aryl group increases. Varying the substitution position is also an effective tuning method, because the ESIPT luminescence wavelength is in the order 6-aryl < 8-aryl < 6,8-diaryl. Although the quantum yields of these compounds are quite low in organic solutions (Φ ∼ 0.01), they generally display a much stronger ESIPT luminescence in the solid state. For all compounds except for 9 having long C6-alkyl chains, the similar emission properties in the dilute frozen matrix and the solid state indicated that ESIPT emission in the solid state is from the monomeric species, even though π-stacked motifs of the HPIP cores and the aryl groups introduced are confirmed by crystallographic analysis. Time-dependent DFT calculations reasonably explained the effect of substitution on ESIPT luminescence in the solid state. The results show that aryl-substitution is a convenient approach to tuning the radiation energy of the ESIPT luminescence of HPIPs without suffering the quenching effect due to intermolecular interactions, and thus a series of PIP compounds that exhibit a wide range of luminescence colors can be realized.

Graphical abstract: The development of aryl-substituted 2-phenylimidazo[1,2-a]pyridines (PIP) with various colors of excited-state intramolecular proton transfer (ESIPT) luminescence in the solid state

Supplementary files

Article information

Article type
Paper
Submitted
26 Jan 2016
Accepted
30 Mar 2016
First published
30 Mar 2016
This article is Open Access
Creative Commons BY-NC license

J. Mater. Chem. C, 2016,4, 3599-3606

The development of aryl-substituted 2-phenylimidazo[1,2-a]pyridines (PIP) with various colors of excited-state intramolecular proton transfer (ESIPT) luminescence in the solid state

T. Mutai, T. Ohkawa, H. Shono and K. Araki, J. Mater. Chem. C, 2016, 4, 3599 DOI: 10.1039/C6TC00376A

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