6.7 Potential Correlation Between Triplet Decay and Rotational …
173
Table 6.5 Emission lifetimes fitted from the emission decays of the crystal 2 monitored at 545 nm
Temp. (K) τ av /∝s a,b τ 1 /∝s a
(A/–)
τ 2 /∝s a
(A/–)
τ 3 /∝s a
(A/–)
τ 4 /∝s a
(A/–)
CHI
298
52.0
2.65 (0.21)
10.8 (0.33)
51.1 (0.19)
141.6 (0.27)
1.010
278
61.4
3.66 (0.19)
11.4 (0.32)
50.6 (0.18)
154.5 (0.31)
0.931
253
48.9
3.02 (0.29)
10.6 (0.37)
46.3 (0.10)
163.9 (0.24)
0.740
233
67.2
3.20 (0.25)
10.7 (0.33)
58.0 (0.15)
197.5 (0.27)
0.924
195
53.5
7.64 (0.55)
26.2 (0.23)
82.1 (0.10)
284.0 (0.12)
0.915
All emission decay was fitted by tail fitting
a λ ex = 370 nm, λ em = 545 nm
b τ av = τ n A n
of short- (ca. 10 μs) and long-lived components (ca. 38 μs) in the temperature interval of 213–298 K (Tables 6.1 and 6.3). However, measurements at 195 K required a
small amount (ca. 10%) of an additional much longer component (110 μs, Table 6.1),
which led to average time constants between ca. 11 and 32 μs in the range of 298 and
193 K. We note that excited state decay occurs within the range of the time constants
for rotation (0.25–100 μs), which may help explain the high kinetic heterogeneity of
the observed emission. One may visualize spectral changes in Fig. 6.9 as resulting
from a superposition of a vibrationally resolved spectrum of 1, from a rotational
minimum, combined with increasing contributions from a broad spectrum that arises
from components experiencing increasingly large vibrations and rotational motion
as the temperature increases. A plot illustrating the variation in k rot and τ av as a
function of temperature is shown in Fig. 6.10.
While the data shown in Figs. 6.6 and 6.7 support the role of phenylene rotation
as the cause for the observed changes in emission, one should consider the fact
that aurophilic interactions defined by Au–Au distances <3.5 Å may also affect
luminescent properties [7]. For example, the deformation of aurophilic interactions,
which include changes in the Au–Au distance, can affect the delocalization and
Fig. 6.10 Qualitative
correlation between the
average emission lifetime
(τ av ) at 540 nm and the
rotation frequency of 1 (k rot. )
173
Table 6.5 Emission lifetimes fitted from the emission decays of the crystal 2 monitored at 545 nm
Temp. (K) τ av /∝s a,b τ 1 /∝s a
(A/–)
τ 2 /∝s a
(A/–)
τ 3 /∝s a
(A/–)
τ 4 /∝s a
(A/–)
CHI
298
52.0
2.65 (0.21)
10.8 (0.33)
51.1 (0.19)
141.6 (0.27)
1.010
278
61.4
3.66 (0.19)
11.4 (0.32)
50.6 (0.18)
154.5 (0.31)
0.931
253
48.9
3.02 (0.29)
10.6 (0.37)
46.3 (0.10)
163.9 (0.24)
0.740
233
67.2
3.20 (0.25)
10.7 (0.33)
58.0 (0.15)
197.5 (0.27)
0.924
195
53.5
7.64 (0.55)
26.2 (0.23)
82.1 (0.10)
284.0 (0.12)
0.915
All emission decay was fitted by tail fitting
a λ ex = 370 nm, λ em = 545 nm
b τ av = τ n A n
of short- (ca. 10 μs) and long-lived components (ca. 38 μs) in the temperature interval of 213–298 K (Tables 6.1 and 6.3). However, measurements at 195 K required a
small amount (ca. 10%) of an additional much longer component (110 μs, Table 6.1),
which led to average time constants between ca. 11 and 32 μs in the range of 298 and
193 K. We note that excited state decay occurs within the range of the time constants
for rotation (0.25–100 μs), which may help explain the high kinetic heterogeneity of
the observed emission. One may visualize spectral changes in Fig. 6.9 as resulting
from a superposition of a vibrationally resolved spectrum of 1, from a rotational
minimum, combined with increasing contributions from a broad spectrum that arises
from components experiencing increasingly large vibrations and rotational motion
as the temperature increases. A plot illustrating the variation in k rot and τ av as a
function of temperature is shown in Fig. 6.10.
While the data shown in Figs. 6.6 and 6.7 support the role of phenylene rotation
as the cause for the observed changes in emission, one should consider the fact
that aurophilic interactions defined by Au–Au distances <3.5 Å may also affect
luminescent properties [7]. For example, the deformation of aurophilic interactions,
which include changes in the Au–Au distance, can affect the delocalization and
Fig. 6.10 Qualitative
correlation between the
average emission lifetime
(τ av ) at 540 nm and the
rotation frequency of 1 (k rot. )