Chemistry Reference
In-Depth Information
O
NN
H
3
CCH
3
H
3
CO
NN
N
N
N
N
36
38
37
CH
3
N
O
HOCH
2
CH
2
OH
N
2NO
-
CH
3
39
40
Lucigenin (40), a dicationic salt derived from
N
,
N
0
-dimethyl-biacridane (27),
was considered to be the most powerful of all synthetic chemiluminescent sub-
stances [
237
-
239
].
Aggregation-induced emission (AIE) is a novel phenomenon exhibited by
propeller-shaped luminogens which are non-emissive in dilute solutions but emit
efficiently upon aggregation [
240
]. AIE luminogens are a class of molecules whose
emissions are induced by aggregate formation in contrast to the more commonly
observed aggregation-caused quenching (ACQ). The AIE effect has attracted
intense interest due to its promising diverse applications in fluorescence sensors,
biologic probes, optoelectronic devices, and mechanochromic smart materials
[
240
]. One of the popular AIE luminogens is the twisted, propeller-shaped
BAE-2 tetraphenylethene (10), described as an ethene stator completely surrounded
by phenyl rotors [
241
]. Its AIE effect has been attributed to the restriction of the
intramolecular rotation (RIR) mechanism [
71
]. A structural evolution in AIE
luminogens is the recent synthesis [
82
,
83
], conformational space determination
[
83
], and AIE characterisation [
82
] of the BAE-2 tetrakis(2-naphthyl)ethene (13),
in which the four “bulky” naphthalene rings can serve as rotors against the ethene
stator to construct the AIE luminogen [
82
,
83
]. Efficient fluorescence of 13 is
induced in the aggregate state, where the non-radiative decay pathway is blocked
[
82
]. Recently it has been reported that the locking of the phenyl rings of the BAE-2
tetraphenylethene (10) by one and two oxygen bridges, leading to the BAE-1
9-diphenylmethylene-9
H
-xanthene (9,X
O) and the thermochromic BAE
dixanthylene (4), respectively, increased the emission efficiency of the luminogen
¼
