Synthesis and Fluorescent Properties of Multi-Functionalized C 70 Derivatives of C 70 (OCH 3 ) 10 [C(COOEt) 2 ] and C 70 (OCH 3 ) 10 [C(COOEt) 2 ] 2 .

Due to the partially reduced π-conjugation of the fullerene cage, multi-functionalized fullerene derivatives exhibit remarkable fluorescent properties compared to pristine fullerenes, which have high potential for application in organic light-emitting diodes (OLEDs). In this study two multi-functionalized C 70 derivatives, C 70 (OCH 3 ) 10 [C(COOEt) 2 ] and C 70 (OCH 3 ) 10 [C(COOEt) 2 ] 2 , with excellent fluorescence properties, were designed and synthesized. Compared with C 70 (OCH 3 ) 10 containing a single kind of functional group, both the C 70 (OCH 3 ) 10 [C(COOEt) 2 ] and C 70 (OCH 3 ) 10 [C(COOEt) 2 ] 2 exhibited enhanced fluorescence properties with blue fluorescence emission. The fluorescence quantum yields of the C 70 (OCH 3 ) 10 [C(COOEt) 2 ] and C 70 (OCH 3 ) 10 [C(COOEt) 2 ] 2 were 1.94% and 2.30%, respectively, which were about ten times higher than that of C 70 (OCH 3 ) 10 . The theoretical calculations revealed that the multi-functionalization of the C 70 increased the S 1 -T 1 energy gap, reducing the intersystem crossing efficiency, resulting in the higher fluorescence quantum yield of the C 70 derivatives. The results indicate that multi-functionalization is a viable strategy to improve the fluorescence of fullerene derivatives.