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Fig. 5 Fully conjugated indeno[1,2-
b
]fluorene 2 and resonance structures of 22
Scheme 23 Preparation of fully conjugated indeno[1,2-
b
]fluorenes 85a-c [
49
]
Fig. 6 Resonance forms of poly(indeno[1,2-
b
]fluorene) 86a,b and model subunit 87a [
61
-
63
]
Fig. 7 Examples of ethynylated (88) and heteroatom-substituted (89) pentacenes [
64
,
68
]
Works by Anthony [
9
,
64
-
67
] and Miller [
68
,
69
], among others [
70
-
73
], have
shown that ethynylogation and/or appending heteroatoms to acenes (e.g., 88-89)
results in a marked increase in stability (Fig.
7
).
Applying the same rationale and synthetic methodology used to obtain
diethynylated pentacenes from pentacene quinone, Haley et al. undertook the
synthesis of tetraethynylindeno[1,2-
b
]fluorenes 92a,b (Scheme
24
) using the
