LI Hai-rong, ZHANG Fu-jia, ZHENG Dai-shun. Investigation on Structural Characteristics of Tris-(8-hydroxyquinoline) Aluminum[J]. Chinese Journal of Luminescence, 2003,24(1): 44-50
LI Hai-rong, ZHANG Fu-jia, ZHENG Dai-shun. Investigation on Structural Characteristics of Tris-(8-hydroxyquinoline) Aluminum[J]. Chinese Journal of Luminescence, 2003,24(1): 44-50DOI:
Investigation on Structural Characteristics of Tris-(8-hydroxyquinoline) Aluminum
An comprehensive understanding of the characteristics of the organic material tris-(8-hydroxyquinoline)aluminum(Alq
3
)is meaningful for organic light-emitting devices(OLEDs). Thin films of Alq
3
are among the most efficient electroluminescent molecular films known to date. Alq
3
samples were synthesized and purified. The purity of samples is up to 98.5%. The electronic and crystallographic structure of Alq
3
has been studied. The results of a joint experimental investigation based on a combination of X-ray diffraction(XRD)spectrum
hydrogen nuclear magnetic resonance(NMR)spectrum
infrared absorption(IRA)spectrum
mass(MS)spectrum
X-ray emission(XRE)spectrum and fluorescence spectrum of Alq
3
have been investigated. The analysis on NMR spectrum of Alq
3
shows that the coordinate interaction between Al
3+
and O ion is more intensive than that between Al
3+
and N ion. Al
3+
hasn't replaced H ion that suggests the Al-O bond is covalent but not ionic bond in Alq
3
molecule. There are still H
+
around O ion. Since there are six coordination bonds around Al
3+
O and N ions are both have strong binding force with Al
3+
. Therefore Alq
3
has two types of geometrical isomers
namely mer isomer and fac isomer. From the IRA spectrum of the Alq
3
the broad characteristic peak at 3417cm
-1
corresponding to OH
-
stretching vibration confirmed that the Al-O are coordinate not ionic bond. The prominent peaks which is the characteristic of the absorption vibration of the aromatic ring skeleton at 1588
1550
1467 and 1400cm
-1
suggests that the conjugate action of aromatic rings in molecule is very strong and all electron orbit of quinolinic rings are π bonding hybridizations. The disagreement between IRA spectrum of Alq
3
and HQ is excellent for indicating that there is a strong coordinate action which affect O bonding heavily between Al
3+
and O ions. From the MS spectrum the ratio of charge/mass of Alq
3
has been achieved. We prospect if a further cleavage occurred
a peaks of Alq
+
after losing a ligand from Alq
2
+
should locate at
m/e
=171. However
the peak was not observed indicating that the state of Alq
+
is difficult to exist. The IRE data shows that the K
α1
2
peaks have shifted comparing to Al due to the perturbation as the ligand gives to 2p electron of Al. The perturbation is related to coordination intensity. The shift of K
β
of Alq
3
mainly resulted from the chemical environment variation around Al atomics. It also relate to binding intensity and coordination number. The intensity of K
β
is lower than that of K
α
The wave length of K
β
is shorter than that of K α.The peak of K
β
shifted to lower energy(about 3.5eV)whereas the peak of K
α1
2
shifted to higher energy(0.3 and 1.6eV)comparing to Al. Surprisingly
a weak adjoint peak at 1537.5eV was observed. We ascribed it to the formation of the hybridization orbit among O
2
s
O
2
p
N
2
s
N
2
p and Al
3
p orbits. Fluorescence data confirmed the existence of a fluorescent species formed between Al ion and 8-hydroxyquinolinol.