Table 1.
Properties of compounds 1–10 (in DMSO) relevant for their photochromism.[a]
|
|
R |
σ p [54] |
S 0‐‐S 1 λ max (ϵ) |
PSD 426 nm |
PSD 526 nm |
PSD 625 nm |
φ t→c |
φ c→t |
φ c→t × ϵ c,426 |
φ t→c × ϵ t,526 |
φ t→c × ϵ t,625 |
half‐life at 25 °C |
thermal cis to trans isomerization |
||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
|
|
|
trans |
cis |
[% cis] |
[% cis] |
[% cis] |
[%] |
[%] |
|
|
|
[days] |
ΔG calc [kJ mol−1] |
ΔG exp [kJ mol−1] |
ΔH exp [kJ mol−1] |
ΔS exp [J mol−1] |
|
1 |
NMe2 |
−0.83 |
– |
483 (6301) |
66 |
22 |
46 |
34 |
nd[b] |
nd[b] |
683 |
10 |
0.70 |
69.1 |
101.6 |
119.5 |
60.0 |
|
2 |
OMe |
−0.27 |
463 (1100) |
452 (1352) |
15 |
58 |
88 |
63 |
51 |
506 |
264 |
8 |
14.3 |
72.4 |
108.7 |
107.6 |
−3.9 |
|
3 |
Me |
−0.17 |
461 (814) |
443 (1572) |
15 |
56 |
90 |
30 |
72 |
963 |
87 |
<1 |
12.5 |
72.0 |
108.4 |
96.0 |
−41.7 |
|
4 |
H |
0.0 |
457 (847) |
441 (1569) |
15 |
62 |
90 |
51 |
48 |
660 |
113 |
3 |
38.1 |
71.4 |
111.1 |
110.3 |
−2.9 |
|
5 |
SMe |
0.0 |
465 (1616) |
452 (2595) |
18 |
52 |
87 |
21 |
37 |
663 |
155 |
4 |
7.4 |
70.0 |
107.1 |
103.6 |
−11.6 |
|
6 |
Cl |
0.23 |
456 (866) |
441 (1546) |
12 |
54 |
89 |
43 |
nd[c] |
nd[c] |
104 |
6 |
32.4 |
72.2 |
110.7 |
113.5 |
9.2 |
|
7 |
OAc |
0.31 |
444 (1324) |
442 (1583) |
12 |
55 |
85 |
57 |
73 |
1010 |
212 |
5 |
14.6 |
72.5 |
108.8 |
99.5 |
−31.0 |
|
8 |
OCF3 |
0.35 |
461 (618) |
441 (1216) |
12 |
52 |
87 |
41 |
nd[c] |
nd[c] |
87 |
2 |
28.6 |
72.4 |
110.4 |
111.0 |
1.9 |
|
9 |
CF3 |
0.54 |
459 (652) |
444 (1290) |
10 |
46 |
83 |
20 |
47 |
511 |
47 |
<1 |
4.4 |
73.1 |
105.8 |
118.1 |
41.5 |
|
10 |
NO2 |
0.78 |
467 (873) |
448 (1673) |
5 |
18 |
45 |
18 |
30 |
384 |
89 |
6 |
0.046 |
67.9 |
94.5 |
100.0 |
18.5 |
[a] Position of absorption maxima (λ max), molar attenuation coefficients (ϵ), photostationary state distributions (PSD) determined under blue (λ exc=426 nm), green (λ exc=526 nm), and red (λ exc=625 nm) light irradiation, quantum yields for forward switching determined at λ=532 nm irradiation (φ t→c), and for reverse switching (φ c→t) determined at λ=445 nm irradiation, photoswitching cross‐sections (φ×ϵ) at blue (λ exc=426 nm), green (λ exc=526 nm) and red (λ exc=625 nm) light, experimentally determined half‐life of the metastable cis isomer at 25 °C, and the calculated and measured activation barrier parameters for the thermal cis‐to‐trans isomerization. [b] Quantum yield for the reverse switching was not determined for compound 1 owing to the presence of the overlapping, bathochromically shifted π–π* band at the λ=445 nm part of the spectrum. [c] Quantum yield values could not be determined for compounds 6 and 8 owing to lack of clear convergence of obtained data to a convincing fit.