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through-space CT has been reported for the SSL.24 Notably, the
calculated emission at lmax = 495 nm for the dimer of 7a was
consistent with that observed experimentally (lmax = 489 nm;
entry 11). However, the observed SSL peak for 7a was narrower
compared to the calculated one. This difference could be
possibly attributed to the additional stabilizing interactions
in the crystal lattice for 7a. Consequently, the TDDFT calcula-
tions provide evidence that an emissive intermolecular
through-space CT band is responsible for the SSL of cationic
perchlorates 3a–d and 7a–d.
In summary, a series of highly emissive planar AIEgens has been
designed by utilizing non-covalent intermolecular p+–p interactions
between Py+ or Im+ cations and aromatic p systems. Structurally
simple salts 3a–d lacking any conventional luminophore moiety
demonstrated high SSL (up to 53% PLQY) in the UV region
(315–350 nm). The introduction of electron donating moieties in
3a–d resulted in bathochromic shifts of the emission maxima, thus
allowing for direct control of emission wavelength. Carbazole-
containing perchlorates 7a–d also demonstrated a remarkable
(up to 800-fold) increase of PLQY as compared to that in MeCN
solution. The presence of iodide ions led to the quenching of the
SSL. Single crystal X-ray analyses confirm the presence of non-
covalent intermolecular interactions between Py+ or Im+ cations and
aromatic p systems in the crystal state of AIEgens 3a and 7a. TDDFT
calculations provide strong evidence that the observed SSL of 3a–d
and 7a–d is a result of intermolecular p+–p interactions that generate
through-space CT bands in the crystal state. The use of the non-
covalent p+–p interactions in the design of AIEgens is a comple-
mentary approach to routinely used means to achieve AIE properties
and to avoid the ACQ effect. We believe that our study will expand
the scope of structural motifs that previously could not be used due
to the ACQ and will open a new avenue for the rational design of
AIEgens.
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This work was funded by ERDF project No. 1.1.1.1/18/A/063.
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Conflicts of interest
There are no conflicts to declare.
21 I. Richter, M. R. Warren, J. Minari, S. A. Elfeky, W. Chen, M. F.
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12666 | Chem. Commun., 2019, 55, 12663--12666
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