Table 2.
UV-Vis absorption properties of 1 in different solvents: peak wavelength of the first absorption band, λabs,1, and of the second absorption band, λabs,2; relative intensity of the first absorption peak, f1; fraction of diketo tautomers according to NMR, fDiketo,NMR; average molar extinction coefficient, <ε> (see text for details).
| Solvent | λabs,1 (nm) | λabs,2 (nm) | f1 | fDiketo,NMR | <ε> (M−1cm−1) |
|---|---|---|---|---|---|
| DCM | 313 (35,000) | 392 (32,900) | 0.79 | 0.85 | 34,600 |
| DMF | 302 | 392 | 0.57 | 44,100 | |
| DMSO | 309 (41,500) | 393 (43,000) | 0.45 | 0.46 | 42,400 |
| EtOH | 311 | 397 | 0.76 | -- |