Table 1 Charging energy E ^N–1–E ^N of different charge states of indigo and Tyrian purple molecules in the gas phase

+2

−10.69

−10.43

+1

−6.49^a

−6.63^a

0

–0.94(0.94)^b

–1.28(1.28)^b

−1

3.27

2.71