Y.-y. Jin et al.
InorganicChemistryCommunications100(2019)129–133
Fig.
2. Normalized
fluorescence
spectra
(λex = 345 nm, c = 28 μM) of (a) s-BSPPy and (b) a-
BSPPy in various solvents. For s-BSPPy, the ratios
(Iexcimer/Imonomer) in DCM (I503/I400), THF (I503/I399),
EtOH (I512/I400), MeCN (I531/I400) are 0.97, 0.63,
0.49, 0.65, respectively. Emission quantum yields of
s-BSPPy and a-BSPPy were determined to be 0.3%
and 2.6%, respectively, in EtOH using anthracene
(Φ = 28%) as reference.
(a)
(b)
molar absorption coefficient (ε) of s-BSPPy is larger than that of a-
BSPPy in both DCM and MeCN.
The tI, IV and tI,V are trivial and there are no short contacts between
the two pyrene moieties of the I–IV or I–V pairs, though there is a short
S2…S2(IV) contact of 3.2595(4) Å between I and IV and a weak hy-
drogen bond of C27-H27…S1(V) (see Table S3 in SI) between I and V.
Thus the possibility of molecular pairs (I–IV) or (I–V) being the excimer
can be excluded. The dimer of (I–II) or (I–III) takes a kind of edge-to-
face λ-shaped conformation and may play the role of excimer, for the
As shown in Fig. 2a, s-BSPPy shows a monomeric emission char-
acterized by the longest peak wavelength at 398 nm in n-hexane, which
is similar to that of a-BSPPy (397 nm in n-hexane). In polar solvents, a
new broad peak at longer wavelength, 503 nm in DCM and red-shifted
to 531 nm in MeCN, appears in the emission spectra of s-BSPPy, which
is the feature of the excimer emission (Fig. 2a). However, no excimer-
The concentration-dependent fluorescence spectra of s-BSPPy and
a-BSPPy in DCM are shown in Fig. 3. The ratio of I503/I400 increases
Meanwhile no excimer emission of a-BSPPy can be observed at any
tI,II and tI,III values are considerable large. The large t value of the I–II or
I–III can be attributed to the C-H…π (II or III) as well as the C-H…C (II
or III) interactions (listed in Table S3 in SI). Taking the I-II pair for
example, the distances of H12 and H13 to the pyrene plane of II are
2.660(16) and 2.672(17) Å respectively, much shorter than the van der
Waals H…π distance of 3.0 Å. The molecules I and II (I and III as well)
are non-parallel oriented with a dihedral angle of 56.5° between their
two pyrene planes (see Fig. 4b). By the C-H…π and C-H…C interac-
tions, a kind of one dimensional zigzag chain has been constructed
along the b-axis direction, in which the adjacent two molecules of the λ-
shaped edge-to-face pair are related each other by 21 screw operation
To figure out the excimer model of the s-BSPPy, the intermolecular
interactions between two neighboring molecules (two-molecule pair)
are considered and can be scaled by the electronic transfer integral, t, of
the concerned molecular pair. The t value can be approached by fol-
pyrene compounds commonly takes a parallel face-to-face π…π geo-
metry. Recently, the non-parallel T-shaped excimer [21] and the tilt-
ported. A tweezer type of pyrene compound, with its two pyrene sub-
units being non-parallel oriented, has been reported to display in-
tramolecular excimer emission [23]. Pyrene derivatives with non-
parallel “herringbone” packing style have also been reported to exhibit
intermolecular “excimer-like” emission [24]. These examples provided,
to a certain extent, some supports to the supposed non-parallel edge-to-
face λ-shaped conformation of the s-BSPPy excimer.
1
2
)
1
(1)
where EHOMO and EHOMO-1 are the energy levels of the HOMO and
HOMO-1 of a two-molecule pair, respectively. All the geometries of the
concerned molecular pairs for the t-calculations are based on the X-ray
structures without optimization.
As shown in Fig. 4a, there are four molecules (II, III, IV, V) [I: (x, y,
z); II: (1-x, 0.5 + y, 1.5-z); III: (1-x, −0.5 + y, 1.5-z); IV: (1-x, 1-y, 1-z);
V: (1-x, −y, 1-z)] around the central molecule I in s-BSPPy crystal. The
calculated t values, corresponding to molecular pairs (I–II), (I–III),
(I–IV), and (I–V) show a sequence of
In recent years, chelatable-S-containing sensors have been designed
to detect various metal ions, such as Ni2+ [25], Hg2+ [26], Ag+ [26].
tI,V (3. 5 meV), tI,IV (21 meV) < <
tI,III (67 meV) tI,II (68 meV).
(a)
(b)
Fig. 3. Fluorescence spectra (λex = 345 nm) of (a) s-BSPPy and (b) a-BSPPy in various concentrations in DCM. For s-BSPPy, the ratios (I503/I400) in concentration of
50, 25, 13, 6.3, 3.1, 1.6, 0.78, 0.39 μM are 1.06, 1.01, 0.73, 0.68, 0.51, 0.46, 0.38, 0.25, respectively.
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