Chemistry Reference
In-Depth Information
Scheme 30 Syntheses of dispiro-IF 106a [
28
]
Scheme 31 Syntheses of dispiro-IFs 106b and 107 [
30
]
Poriel, and coworkers. For instance, they prepared dispiro-fused [1,2-
b
]IF 106a in
an attempt to overcome issues in fluorene-utilizing OLEDs involving defects
perturbing the color outputs of these devices (Scheme
30
)[
28
,
81
]. Beginning
with 2,2
00
-diiodo-
p
-terphenyl (104), lithiation and subsequent addition of
fluorenone furnished diol 105a. Treatment with AcOH/HCl at reflux then gave
106a in 55% yield over the two steps. Devices utilizing 106a showed improved
blue-emission without green contamination from defects [
82
].
Further investigation by the same group found that, depending on the substrate
and reaction conditions, two different products were often produced in this cycliza-
tion, thus limiting somewhat the scope of this synthesis to incorporate broader
functionalization. When the fluorene moiety possessed steric bulk on the periphery,
formation of a second product, the indeno[2,1-
a
]fluorene regioisomer, is favored.
Its formation is also typically favored by use of less polar solvents and higher
temperatures. In the reaction shown in Scheme
31
, 106b is formed in a ratio with
107 of roughly 3:1 when the reaction is done in DCM but the ratio shifts to 1:2 if the
reaction is performed in acetonitrile, regardless of temperature. Adding even more
steric bulk on the fluorene favors the [2,1-
a
]IF to an even greater degree,
suppressing formation of the [1,2-
b
]IF isomer completely if sufficient bulk exists
[
30
].