Table 2. Vertical Excitation Energies in eV (nm), Oscillator Strengths (f), and Static Dipole Moments (μ) in Debye (D) for the Low-Lying Singlet Excited States of the Purine Tautomers and 9-Methylpurine at the MS-CASPT2//SA10-CASSCF(16,12)/ANO-L Level of Theory.
| state | ΔE, eV (nm) | f | μ (D) |
|---|---|---|---|
| N9H purine | |||
| S1 nπ* | 4.05 (306) | 0.0038 | 3.31 |
| S2 ππ* | 4.68 (265) | 0.0724 | 3.00 |
| S3 nπ* | 4.94 (250) | 0.0027 | 1.88 |
| S4 ππ* | 5.02 (247) | 0.0306 | 7.40 |
| N7H purine | |||
| S1 nπ* | 4.00 (309) | 0.0006 | 5.03 |
| S2 ππ* | 4.58 (270) | 0.0440 | 3.57 |
| S3 ππ* | 4.85 (255) | 0.1504 | 8.84 |
| S4 nπ* | 4.97 (249) | 0.0000 | 4.25 |
| 9-methylpurine | |||
| S1 nπ* | 4.05 (306) | 0.0036 | 3.93 |
| S2 ππ* | 4.69 (265) | 0.0609 | 3.62 |
| S3 ππ* | 4.85 (255) | 0.0384 | 8.33 |
| S4 nπ* | 4.96 (249) | 0.0018 | 2.43 |