Topic
Steric effects
About: Steric effects is a research topic. Over the lifetime, 16112 publications have been published within this topic receiving 319615 citations. The topic is also known as: steric hindrance.
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TL;DR: The relaxation of the excited-state structure of DPAC and its numerous analogues could be mimicked by model structures Mx-My, demonstrating for the first time the the conformation change from bent-to-planar and hence a large range of energy-gap tuning of polycyclic conjugated structures controlled by the steric hindrance.
Abstract: ortho-Methyl effects are exploited to tune steric hindrance between side-chain N,N'-diaryls and polycyclic dihydrodibenzo[a,c]phenazine, and in turn control the conformations of N,N'-diphenyl-dihydrodibenzo[a,c]phenazine (DPAC) and its ortho-methyl derivatives Mx-My (x=0, 1 or 2, y=1 or 2, x and y correlate with the number of methyl groups in the ortho-positiond of N,N'-diphenyl). The magnitude of steric hindrance increases as x and y increase, and the V-shaped dihydrodibenzo[a,c]phenazine skeleton is gradually tuned from a bent (DPAC) to planar (M2-M2) structure in the ground state. As a result, the relaxation of the excited-state structure of DPAC and its numerous analogues could be mimicked by model structures Mx-My, demonstrating for the first time the the conformation change from bent-to-planar and hence a large range of energy-gap tuning of polycyclic conjugated structures controlled by the steric hindrance.
68 citations
TL;DR: In this article, a series of free-base octaalkylporphyrins having halogen substituents at different sites on the nucleus has been examined by photophysical methods.
Abstract: A series of free-base octaalkylporphyrins having halogen substituents at different sites on the nucleus has been examined by photophysical methods. In general, halogenation decreases the fluorescence yield and lifetime, increases triplet formation and decreases the resultant triplet lifetime. The magnitude of these effects, which increases in the order F < Cl < Br < I and is dependent on the site of halogenation (benzylic position of alkyl < β position of pyrrole < meso position) can be explained in terms of a modified spin–orbit coupling theory. Multiple halogenation at meso positions, however, can cause secondary effects, due to steric crowding (bromine) or electron redistribution (fluorine). Photophysical data derived from the full set of meso-fluorinated porphyrins can be described quantitatively in terms of combined spin–orbit coupling and electronic perturbation in which a fluorine substituent deactivates adjacent meso sites but activates the site opposite the substituent.
68 citations
TL;DR: In this article, the authors studied the catalytic properties of nitrogen-containing model compounds such as pyridine, quinoline, acridine, pyrrole and carbazole and found that saturation of the heteroaromatic rings always occurs prior to any cleavage of C-N bonds.
68 citations
68 citations
TL;DR: The unsaturated 16e{sup -} fragment has been observed to insert into the sulfur-carbon bond in a variety of substituted dibenzothiophenes to give a six-membered metallacycle product.
68 citations