(ppm), J Hz): 3.58–3.72 (m, 12H, CH2-5, CH2-6, CH2-8, CH2-9,
CH2-11, CH2-12), 3.77–3.88 (m, 4H, CH2-3, CH2-14), 3.96–4.08
(m, 4H, CH2-2, CH2-15), 5.94 (d, J = 9.7, 1H, H-20), 6.39–6.52
(m, 3H, H-17, H-21, H-22), 7.11–7.29 (m, 6H, H-Ar), 7.30–7.38
(m, 4H, H-Ar). 13C NMR (63 MHz, CDCl3, d (ppm)): 68.56,
69.34, 69.63, 69.91, 70.53, 70.59, 70.66, 70.68, 82.43 (s, quat-C),
102.61, 113.23, 113.38, 123.01, 126.35, 126.87, 127.34, 127.97,
142.80, 144.83, 147.33, 150.14. Calculated for C31H34O7·2H2O
(%): C, 67.13; H, 6.91. Found (%): C, 67.68; H, 6.96.
Protonated amino acids were prepared by dissolving neutral
b-alanine, g-aminobutyric, e-aminocaproic, and w-aminocaprylic
acids (all purchased from Aldrich) in acetonitrile solution of
perchloric acid at ambient temperature. After being stirred during
24 h, the solution was filtered and the solvent was evaporated. The
residue was additionally kept in a lyophilizer during 20 h.
of the chromene and one of the ligands was prepared. Using
spectrometer «Avantes AvaSpec-2048», a spectrum was recorded
(with 0.5–2 s interval between measurements) upon continuous
irradiation of the sample solution. Each sample was irradiated
during the same time. Upon cessation of the irradiation, the
spectrum was recorded until full bleaching or at least the intensity
of a long wavelength band was decreased by half. Assuming that
the complex equilibria establish much faster than the bleaching
occurs, the processes were analyzed using the following equations
(consult ESI† for details on the kinetic scheme):
k0 + k11K11CL
1+ K11CL
kobs
=
(1)
k0 + k11K11CL + k12K11K12CL2
1+ K11CL + K11K12CL2
(2)
kobs
=
2. UV–vis spectroscopy measurements
where CL denotes molar concentration of the amino acids or
ammonium perchlorates; kobs, k0, k11, and k12 denote the observed
bleaching rate constant and the rate constants for the free
chromene, 1 : 1 and 1 : 2 complexes, respectively; K11 and K12
represent the stability constants of the 1 : 1 and 1 : 2 complexes,
respectively.
Electronic absorption spectra were recorded on spectrophotome-
ters «Specord M40» and «Avantes AvaSpec-2048». Spectra of the
colored forms were obtained when samples in the spectrometer cell
were simultaneously exposed to continuous irradiation, generated
by Hg high pressure lamp 120W.
Applying eqn (1) and 2 to the experimental data, we estimated
the stability constants of the complexes and determined the
thermal relaxation rate constants of the open forms in these
complexes.
3. NMR spectroscopy measurements
NMR spectra were recorded on a Bruker 300 spectrometer
(1H, 300 MHz) equipped with QNP probe or on a Bruker
500 spectrometer (1H, 500 MHz) equipped with TXI probe,
using standard sequences. Data sets were processed using Bruker
Topspin 1.3 software. Photoirradiation was carried out directly
into the NMR tube in a home-built apparatus with a 1000 W
high-pressure Hg-Xe lamp equipped with a filter (Schott 11FG09:
259 < l < 388 nm with lmax = 330 nm, T = 79%) to select UV light
and an interferential filter (l = 313 nm and T = 16%).
Acknowledgements
The NMR facilities were funded by the Region Nord-Pas de Calais
(France), the Ministere de la Jeunesse de l’Education Nationale
et de la Recherche (MJENR), and the Fonds Europeens de De-
veloppement Regional (FEDER). Part of this collaborative work
was realized within the framework GDRI CNRS 93 “Phenics”
(Photoswitchable Organic Molecular Systems & Devices).
4. Stability constant measurements
Spectrophotometric titration was used for determining the stabil-
ity constants for complexes of chromene 1 (its closed forms, before
irradiation) with protonated amino acids.52,53 The procedure was
as follows: to a solution of the ligand in acetonitrile (~10-4 M),
aliquots of the substrate solution (b-alanine, g-aminobutyric, e-
aminocaproic, or w-aminocaprylic acids perchlorates in acetoni-
trile, ~10-2–10-3 M) were added stepwise, recording an absorption
spectrum after each addition. By analyzing spectral changes
during the course of the titration, conclusions on complex com-
position and stability were drawn. The stability constants of the
complexes were determined by applying the SPECFIT/3254 soft-
ware to experimental data considering the following equilibrium:
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