Chemistry Reference
In-Depth Information
Table 2 Photophysical properties of multiethynyl substituted corannulene derivatives
a
[
39
]
Compound
Absorption
ʻ
a
(nm)
Emission
ʻ
f
(nm) Quantum yield (
ʦ
f
)
1
320
423
0.03
30 (R
¼
Ph)
400, 363
345
434, 415
0.20
44 (R
¼
Ph)
425, 378
359, 320
469, 446
0.75
41 (R
¼
Ph)
450, 400, 356, 305
500, 473
0.83
41 [R
¼
3,4,5-C
6
H
2
(OC
12
H
25
)
3
]
370
529
0.67
41 (R
¼
SiMe
3
)
331
475, 449
0.17
49 (R
¼
Ph)
358, 324
485, 465
0.12
49 [R
¼
3,4,5-C
6
H
2
(OC
12
H
25
)
3
]
376, 332
542
0.37
49 (R
¼
SiMe
3
)
339, 303
468, 452
0.05
a
Measured in DCM
(0.72
).
Although the structure of lowly soluble decachlorocorannulene (52) has not yet
been analyzed by X-ray crystallography, its bowl depth was determined to be
0.51
)[
80
] is smaller than that of 1,3,5,7,9-pentamethylcorannulene (0.85
Å
Å
obtained at
B3LYP/cc-pVDZ [
71
]. The bowl depth of deca-substituted corannulenes C
20
R
10
strongly depend on the
Å
by gas-phase electron diffraction study [
72
], and 0.49
Å
substituents,
their values
following the order
arylethynyl
>
methyl
>
Cl SPh
>
Ar.
It was observed that 1,3,5,7,9-pentamanisylcorannulene 50 (R
¼
manisyl) has an
unusually large bowl depth (0.91
) and barrier to bowl inversion (12.1 kcal/mol)
[
70
]. The increase of these values may be ascribed to van der Waals attractive
forces among the
endo
methyl groups in the conformational ground state.
Notably, the number of attached arylalkynyl pendant groups correlates with an
increase in the bowl depth of the corrannulene nucleus; the bowl depth for the
multi-ethynylcorannulenes follows the sequence: 49
Å
>
41
>
44 based on the
crystallographic analysis [
39
].
Photophysical properties of a series of ethynyl substituted corannulenes have
been systematically studied (Table
2
) and they are tunable by varying the number
and the kind of ethynyl substituents [
39
]. Most multi-ethynylcorannulenes in
solution display high-quantum-efficiency luminescence and variable emission
wavelengths. In contrast to the parent compound corannulene (1), the batho-
chromatic effects on absorption and emission wavelengths and the fluorescence
quantum yields (
ʦ
f
) for the phenylethynyl-substituted series generally increase
with the number of acetylene moieties. Pentakis(phenylethynyl)corannulene 49
(R
Ph) is the exception, and its low quantum yield can be explained by (1) the
Ham effect [
102
], in which high symmetry leads to forbidden transitions between
the ground and excited states, and (2) the deeper bowl depth, which causes the
structure to deviate from planarity [
103
]. Moreover, arylethynyl substituents cause
a greater red shift and higher quantum yield than (trimethylsilyl)-ethynyl groups.
Additional electron-rich moieties on arylethynyl, such as 3,4,5-tridodecoxyphenyl,
also strongly affect photophysical properties.
¼
