Communications
Table 3: Emission and absorption characteristics of 3 and 18–21 in CH2Cl2.[a]
Compound
Ff[b]
lem[nm]
loge
labs[nm]
t[ns]
kr[sÀ1
]
kd[sÀ1
]
kr/kd
3
0.01
0.63
0.60
0.18
0.41
328
378
378
355
433
4.70
4.79
4.76
4.62
4.62
306
339
340
322
355
1.98
1.62
1.75
2.40
3.47
5.06106
3.90108
3.45108
7.50107
1.18108
5.01108
2.29108
2.28108
3.42108
1.70108
0.01
1.70
1.52
0.22
0.70
18
19
20
21
[a] All spectra were measured at 295 K. [b] Quantum yield is calculated relative to quinine (Ff =0.55 in 0.1m H2SO4).
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lenes (5 and 6) with single and double banana structures are
highly efficient light emitters despite the interruption of the
p conjugation. The emission efficiency is interpreted in terms
of kr and kd values. A new concept on movability of the
dipolar dimethoxyphenylethynylpyridine structure (in other
words, the number of dipolar diad units structurally equiv-
alent to 17) in the excited singlet state molecules is presented
to explain the results. A quite contrasting effect of the solvent
on the emission efficiency was observed for 5 and 6, which
might be explained by the marked disparity between the
difference density distribution in the excited states of 5 and 6.
The emission efficiency of 3 (very weak fluorophore) was
found to dramatically increase on formation of a TiIV com-
plex. The main reason for this is ascribed to the increase in the
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=
electron-accepting ability of the pyridine C N groups by the
coordination to TiIV centers.
Received: June 24, 2005
Published online: October 11, 2005
À
Keywords: C C coupling · conjugation · luminescence ·
.
solvent effects · titanium
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ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2005, 44, 7040 –7044