| Compound | Absorption maximum, λmax [nm] | ||
| Chloroform | Dimethyl sulfoxide | Methanol | |
| 8HQ | 244 | 319 | 241 |
| Cu(II)-8HQ | 262 | 264 | 257 |
| Co(II)-8HQ | 259 | 264 | 255 |
| Ni(II)-8HQ | 247 | 268 | 259 |