Communication
Dalton Transactions
from the other solvents. The blue emission is more consistent
with the solid-state fluorescence properties of 2f alone (Fig. 7).
Hexane showed the least effect, as might be expected for a
non-coordinating solvent.
In conclusion, we have synthesised a range of Lewis basic
imines and studied their adducts with Lewis acidic boranes by
various spectroscopic methods. In the case of the nButyl sub-
stituted imine, strong adduct formation was observed with
B(C6F5)3. The stability of this Lewis pair adduct allowed the
solution-state electronic properties to be determined showing
that ICT electronic transitions give rise to new visible region
absorption and fluorescence properties. For
a selected
example, sufficient air/moisture stability of the adduct facili-
tated an exploration of its vapochromic properties with a small
range of organic solvents. These findings suggest that with
further optimisation Lewis pair adducts may be applicable to
the design of new vapochromic materials via modulation and
discrimination of charge transfer fluorescence properties.
Fig. 7 Solid-state film fluorescence spectra of 2f and 2f·B(C6F5)3
(λex = 330 nm).
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
S. J. A. P. thanks the Leverhulme Trust for financial support
(RPG-2015-359).
Notes and references
1 G. C. Welch, R. R. San Juan, J. D. Masuda and
D. W. Stephan, Science, 2006, 314, 1124.
2 For recent reviews, see: (a) D. W. Stephan and G. Erker,
Angew. Chem., Int. Ed., 2015, 54, 6400, (Angew. Chem., 2015,
127, 6498); (b) D. W. Stephan, Acc. Chem. Res., 2015, 48, 306;
(c) D. W. Stephan, J. Am. Chem. Soc., 2015, 137, 10018.
3 (a) T. Mahdi and D. W. Stephan, J. Am. Chem. Soc., 2014,
136, 15809; (b) D. J. Scott, M. J. Fuchter and A. E. Ashley,
J. Am. Chem. Soc., 2014, 136, 15813; (c) É. Dorkó, M. Szabó,
B. Kótai, I. Pápai, A. Domján and T. Soós, Angew. Chem.,
Int. Ed., 2017, 56, 9512, (Angew. Chem., 2017, 129, 9640);
(d) M. Bakos, Á. Gyömöre, A. Domján and T. Soós, Angew.
Chem., Int. Ed., 2017, 56, 5217, (Angew. Chem., 2017, 129,
5301).
4 (a) Á. Gyömöre, M. Bakos, T. Földes, I. Pápai, A. Domján
and T. Soós, ACS Catal., 2015, 5, 5366.
5 (a) V. Fasano, J. E. Radcliffe and M. J. Ingleson, ACS Catal.,
2016, 6, 1793; (b) L. C. Wilkins, J. L. Howard, S. Burger,
L. Frentzel-Beyme, D. L. Browne and R. L. Melen, Adv.
Synth. Catal., 2017, 359, 2580; (c) V. Fasano and
Fig. 8 2f·B(C6F5)3 adduct filter strips under UV light (λ = 365 nm)
exposed to different solvent atmospheres over time (a) blank (b) hexane
(c) toluene (d) Et2O (e) THF (f) MeOH.
strips showed a similar appearance. Firstly, the visual green
fluorescence was still observed after 4 days indicating that
solid 2f·B(C6F5)3 is relatively bench stable under these con-
ditions. Secondly, the green fluorescence signal correlates well
with the solid-state luminescence measurements on 2f·B
(C6F5)3 (Fig. 7). Using a simple set-up (Fig. S84, ESI†), the
impregnated filter strips were then exposed to selected solvent
vapours. The visualised fluorescence from the papers strips
was recorded at specific time intervals (Fig. 8). The coordinat-
ing solvents Et2O, THF and MeOH showed a more rapid
change in visualised fluorescence output than non-coordinat-
ing solvents. After 30 min the THF sample had already lost
green fluorescence, suggesting a disruption in the integrity of
the fluorescent 2f·B(C6F5)3 adduct. Interestingly, the protic
solvent methanol showed a rapid loss in green fluorescence
and evolution of a blue emission, allowing easy discrimination
M. J. Ingleson, Chem.
– Eur. J., 2017, 23, 2217;
(d) G. Ghattas, C. Bizzarri, M. Hölscher, J. Langanke,
C. Gürtler, W. Leitner and M.-A. Subhani, Chem. Commun.,
2017, 53, 3205.
Dalton Trans.
This journal is © The Royal Society of Chemistry 2018