Table 4. Vertical Wavelength (λ, nm) and the Oscillator Strengths (f) Contributing to S1 → S0 Electronic Transitions of Investigated Molecules, Calculated by the TD-B3LYP/6-31g(d,p) Method in Methanol Solvent. The excitation wavelengths varied from 366 to 380 nm.
| compounds | λPL,expmax (nm) | fmax | major contribs (%) | minor contribs (%) |
|---|---|---|---|---|
| NBD-S1 | 292 | 0.1476 | L → H – 4 (54%), L → H – 2 (23%) | L + 4 → H (8%) |
| 366 | 0.0646 | L + 1 → H (80%) | L + 1 → H – 1 (13%) | |
| 515 | 0.5543 | L → H (88%) | L → H – 1 (8%) | |
| λPL,expmax = 522 nm25 | ||||
| NBD-S2 | 287 | 0.0226 | L + 2 → H – 3 (79%) | L → H – 4 (3%), L + 10 → H – 3 (8%) |
| 366 | 0.0625 | L + 1 → H (90%) | L + 1 → H – 2 (4%) | |
| 513 | 0.5486 | L → H (95%) | ||
| λPL,expmax = 521 nm25 | ||||
| NBD-S3 | 290 | 0.1458 | L → H – 3 (73%) | L + 3 → H (12%) L → H – 4 (8%) |
| 367 | 0.059 | H → L + 1 (95%) | ||
| 507 | 0.5614 | L → H (97%) | ||
| λPL,expmax = 516 nm25 | ||||
| NBD-S4 | 291 | 0.1482 | L → H – 3 (73%), | L + 4 → H (12%), L → H – 5 (5%), L → H – 4 (3%) |
| 365 | 0.0558 | L + 1 → H (95%) | ||
| 503 | 0.5636 | L → H (97%) | ||
| λPL,expmax = 542 nm25 | ||||