An enhancement in the external quantum efficiency (QE) of red phosphorescent organic light‐emitting devices (OLEDs) by using facially encumbered and bulky meso‐aryl substituted PtII porphyrin complexes is demonstrated. The maximum external QEs of phosphorescent OLEDs doped with the facially non‐encumbered PtII porphyrin complex 1 [5,15‐bis[4‐(4,4‐dimethyl‐2,6‐dioxacyclohexyl)phenyl]‐2,8,12,18‐tetrahexyl‐3,7,13,17‐tetramethylporphyrin platinum(II)], the facially encumbered PtII porphyrin complex 2 [5,15‐bis(2,6‐dimethoxyphenyl)‐2,8,12,18‐tetrahexyl‐3,7,13,17‐tetramethylporphyrinato platinum(II)], the PtII porphyrin complex 3 that bears bulkier 3,5‐di‐tert‐butylphenyl substituents [5,15‐bis(3,5‐di‐t‐butylphenyl)‐2,8,12,18‐tetrahexyl‐3,7,13,17‐tetramethylporphyrin platinum(II)], and the “doubly‐decamethylene‐strapped” PtII porphyrin complex 4 were 1, 4.2, 7.3, and 8.2 %, respectively. The trend of increasing QE values in the order of 1 < 2 < 3 < 4 may be related to facial encumbrance and steric bulkiness of meso‐aryl substituted PtII porphyrin complexes. Especially, in the case of the PtII porphyrin 4, it is considered that the “double straps” play an important role in restricting rotational freedom of the meso‐aryl substituents. The triplet excited‐state lifetimes for PtII porphyrins 1–4 in OLEDs at an injection current density of 0.55 mA cm–2 were 80, 103, 140, and 152 μs, respectively. We believe that the trend of increasing triplet lifetime in going from 1 to 4 is correlated with suppressing non‐radiative decay.

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14π‐Electrocyclization across the two pentafulvenoid moieties of pentafulvene 1 occurs upon heating to provide dicyclopenta[a,d]cyclooctene 2 [Eq. (1)]. The nonalternant hydrocarbon 2 shows diatropic character and a distinctive absorption spectrum with the longest wavelength maximum at 767 nm.

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The title compound, l-acryloyl-1,3,5-cycloheptatriene (3), phosphoric acid and formic acid at room temp. produced was prepared from 1,3,5-~ycloheptatriene in four steps, and 3,8-dihydro-l(2H)-azulenone (6) and 3,3a-dihydro-l(2H)-subsequently its Nazarov cyclization of 3 was studied in or-azulenone (7) in yields of 46 and 13% respectively. Using der to develop a novel synthetic pathway to dihydro-l(2H)-stannic chloride as the acid in the reaction gave 6 and 7 in a azulenone. While the reaction of 3 in sulfuric acid afforded slightly better combined yield. 1-tetralone (5) in a low yield, the reaction in a mixture of The Nazarov reaction ['] is an electrocyclization involving the distribution of 4 7t electrons along a five-carbon atom chain. In the case of the ring closure of 3-hydroxypentadienylic cations, generated commonly from divinyl ketone derivatives in the presence of a protic or Lewis acid, this leads specifically to cyclopentenone derivatives. Because of its applicability to a wide variety of substrates, this reaction is one of the most convenient methods for constructing cyclopentenone-annelated carbocycles. L2] It is puzzling that, whilst there are several methods for the preparation of the azulene ~keleton, [~] has not yet been reported. In view of the synthetic importance of dihydroazulenones, we have directed our interests toward development of a new synthetic pathway to these compounds. Herein we describe both the convenient synthesis of 1 -acryloyl-1,3,5-cycloheptatriene (3) and its Nazarov reaction, resulting in the formation of two new dihydroazulenones. Results and DiscussionAmong several possible isomers for the purpose we chose l-acryloyl-1,3,5-cycloheptatriene (3) as a substrate for the Nazarov reaction. This choice was made from viewpoint of synthetic accessibility (vide infra). It was prepared in three steps starting from l-acetyl-l,3,5-cycloheptatriene (l), which is readily available in a large quantities via the Results of the Nazarov cyclization of 3 are summarized in Table 1. Attempts to carry out the reaction in the presence of sulfuric acid met with little success; in methanol the addition product 4 was obtained in a yield of 81 'YO, and in sulfuric acid 1-tetralone (5) was formed as the sole isolable product in a yield of 10%. Under less acidic conditions the expected products were obtained; in a mixture of phosphoric acid and formic acid at room temp. 3 gave the 3,8-and 3,3a-dihydro-l(2H)-azulenones (6 and 7) in yields of 46% and 13%, respectively. We have also examined the use of Lewis acids in the reaction instead of protic acids. While using stannic chloride in dichloromethane as the solvent at 0°C gave 6 and 7, in yields of 47% and 27% respectively, the reactions in the presence of other Lewis acids, such as boron trifluoride -diethyl ether, aluminium chloride and ferric chloride at 0°C gave a complex mixture of products, which included dihydroazulenones and 1-tetralone.The structures of 6 and 7 were supported by their spectroscopic data, and comparison of this data with that of