Table 2. Photophysical properties of [4]helicenes in acetonitrile.
| Molecule | Functional group (Y) | λ max/nm (εmax/L mol–1 cm–1) | fwhm/cm–1 | λ em/nm | Φ a | τ b /ns | k R c /106 s–1 | k NR c /106 s–1 |
| 1 | H | 616 (14 000) | 2460 | 667 | 0.13 | 5.5 | 23.6 | 158.2 |
| 5 | NO2 | 575 (12 000) | 2440 | 624 | 0.35 | 14.5 | 24.1 | 44.8 |
| 6 | CHO | 582 (10 750) | 2500 | 640 | 0.37 | 16.2 | 22.8 | 38.9 |
| 7 | NH2 | 698 (6560) | 3280 | — | — | — | — | — |
| 8 | NMe2 | 675 (5580) | 3280 | — | — | — | — | — |
| 9 | N3 | 644 (8790) | 2890 | — | — | — | — | — |
| 10a | Triazolo-Ph | 606 (11 670) | 2430 | 670 | 0.19 | 8.5 | 22.4 | 95.3 |
| 10b | Triazolo-p-CF3-Ph | 605 (12 820) | 2370 | 665 | 0.24 | 10.4 | 23.1 | 73.1 |
| 10c | Triazolo-p-NMe2-Ph | 607 (11 520) | 2420 | — | — | — | — | — |
| 11 | CN | 585 (12 880) | 2290 | 631 | 0.55 | 19.1 | 28.8 | 23.6 |
| 12 | CHC(CN)2 | 598 (11 550) | 2540 | 658 | 0.28 | 15.1 | 18.5 | 47.7 |
| 13a | CH CH-Ph | 638 (6710) | 2910 | — | — | — | — | — |
| 13b | CH CH-p-NO2-Ph | 638 (8090) | 2810 | — | — | — | — | — |
| 13c | CH CH-p-CF3-Ph | 640 (8810) | 2840 | — | — | — | — | — |
| 13d | CH CH-p-NH2-Ph | 660 (5600) | 3170 | — | — | — | — | — |
| 13e | CH CH-m-diCF3-Ph | 636 (8750) | 2770 | — | — | — | — | — |
| 13f | CH CH-m-diOMe-Ph | 644 (7960) | 2860 | — | — | — | — | — |
| 14 | OH | 659 (7450) | 3040 | — | — | — | — | — |
| 15 | OMe | 653 (7750) | 3030 | — | — | — | — | — |
| 16 | CO2– | 626 (10 400) | 2840 | 709 | 0.01 | — | — | — |
| 17a | COMe | 593 (9080) | 2430 | 657 | 0.26 | 12.0 | 21.7 | 61.7 |
| 17b | COPh | 598 (9130) | 2450 | 659 | 0.27 | 12.1 | 22.3 | 60.3 |
| 17c | CO2Et | 592 (12 200) | 2370 | 653 | 0.33 | 14.0 | 23.6 | 47.9 |
| 17d | CO2Ph | 586 (11 700) | 2380 | 641 | 0.39 | 16.3 | 23.9 | 37.4 |
| 17e | COSEt | 596 (11 100) | 2370 | 655 | 0.34 | 14.3 | 23.8 | 46.2 |
| 17f | CONHPr | 609 (11 500) | 2420 | 667 | 0.19 | 8.3 | 22.9 | 97.6 |
| 17g | CONEt2 | 615 (10 300) | 2450 | 678 | 0.13 | 6.2 | 21.0 | 140.3 |
aReference: cresyl violet (Φ = 0.54 in methanol), estimated error ± 10%.
bExcitation at 470 nm.
cWith kR = Φ/τ and kNR = (1 – Φ)/τ.