Blue-green photoluminescence from pyridine-C60 adduct

doi:10.1016/S0009-2614(00)01115-5

Chemical Physics Letters

Volume 330, Issues 3–4, 10 November 2000, Pages 262-266

https://doi.org/10.1016/S0009-2614(00)01115-5 Get rights and content

Abstract

The freshly prepared solution of C₆₀ in pyridine has a purple-pinkish color, which turns gradually into a brown color. We report for the first time the observation of a bright blue-green photoluminescence from the brown C₆₀/pyridine solution upon UV excitation. The luminescent species is identified to be the zwitterionic adduct formed between pyridine and C₆₀ as revealed by $^{1} H$ -NMR, mass spectra, and the solvatochromic effect of the photoluminescence to protic solvent. The fluorescence excitation spectra of the luminescent species and the dependence of the luminescence on excitation wavelength are also reported. C₇₀ in pyridine shows similar phenomena.

Introduction

Three dimensional conjugation of the π electron system in C₆₀ makes it a potentially attractive chromophore and fluorophore. However, underivatized pure C₆₀ only fluoresces very weakly in the 620–900 nm region with a quantum yield of 3.2×10⁻⁴ and a lifetime of 1.2 ns that are independent of solvents and excitations [1], [2], [3]. Recently, strong photoluminescence and electroluminescence were observed from the derivatized C₆₀[4], [5], leading to a successful fabrication of a fullerene-based white light LED [5].

Optical properties of the dissolved C₆₀ are affected by the nature of solvents [6], [7], [8], [9], [10], some of which form adducts with C₆₀ in the presence of light [11], [12]. Here, we report for the first time that the purple-pinkish color of a freshly prepared C₆₀/pyridine solution changes gradually to brown color and stabilizes thereafter. Unlike the purple-pinkish C₆₀/pyridine solution, which shows no `abnormal' photoluminescence, the brown C₆₀/pyridine solution emits a bright blue-green photoluminescence centered at ca. 470 nm upon UV excitation. We attribute the observed photoluminescence from the brown C₆₀/pyridine solution to new zwitterionic species formed by the adduction of the solvent pyridine molecule(s) to C₆₀, as revealed by $^{1} H$ -NMR and mass spectra, as well as the solvatochromic effect in the presence of protic solvent (vide infra).

Section snippets

Results and discussion

C₆₀ (99.9%) was dissolved in pyridine (99.9%, Fisher Scientific) sonically. The freshly prepared solution exhibits a purple-pinkish color, consistent with the previous report [6]. However, the color of this solution turns gradually from purple-pinkish into brown and stabilizes thereafter. The presence of light, especially UV radiation, speeds up the color change process. The observed color change of C₆₀/pyridine solution can be accounted for by the change of UV-visible absorption spectra shown

Conclusions

In summary, we observed a color change from purple-pinkish to brown in the C₆₀/pyridine solution. We showed that the brown solution emits a bright blue-green luminescence upon UV excitation. Both the color change and the blue-green luminescence are attributed to the formation of the zwitterionic adducts between pyridine and C₆₀, as supported by its $^{1} H$ -NMR and mass spectra, as well as the strong solvatochromic effect of the photoluminescence in the presence of protic solvent. We also observed

Acknowledgements

This work is supported by the grants from RGC-HK, HKUST, and NNSFC-RGC. The authors thank Lin Guo, Tingbin Wen and Laura Cao for their helpful discussion and the acquirement of NMR and mass spectra.

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Blue-green photoluminescence from pyridine-C60 adduct

Abstract

Introduction

Section snippets

Results and discussion

Conclusions

Acknowledgements

Opt. Commun.

Chem. Phys.

J. Chem. Soc., Perkin Trans.

Top. Curr. Chem.

J. Am. Chem. Soc.

J. Am. Chem. Soc.

Chem. Commun.

J. Phys. Chem.

Blue-green photoluminescence from pyridine-C₆₀ adduct