Mechanism of Photodimerization of Acenaphthylene

Abstract

The mechanism of photodimerization of acenaphthylene (ACN) has been investigated in order to elucidate the roles of the singlet and the triplet excited states of ACN in the formation of the Zand E-dimers in several solvents. The quantum yields and the ratio of the produced Z-to E-dimer were determined under irradiation of ACN at 435.8 nm in several solvents (1,2-dichloroethane, acetonitrile, cyclohexane, benzene, methanol, and DMF) over a wide concentration range (2.0 × 10 -4 -2.0 M) in the absence of additives and in the presence of 1,2-dibromoethane, a heavy-atomcontaining solvent; Eosin-Y, a triplet sensitizer (irradiated at 546.1 nm); and ferrocene, a triplet quencher. On irradiation of ACN in dilute solution, the initially generated S 1 state crosses over to the T 1 state, though with low quantum yield, before reaction with the ground state ACN can occur due to the very short lifetime of the S 1 state, and the resultant T 1 state reacts with ground state ACN to give a mixture of the Z-and E-dimers in a ratio that depends on the solvent employed. In more concentrated solution, the S 1 state reacts with ACN before intersystem crossing to the T 1 state can occur, affording exclusively the Z-dimer.

Photochemical Dimerization of Acephenanthrylene and the Heavy Atom Effect

“…The exclusive formation of the cis dimers in aerated solvents suggests that an excimer state may intervene, similar to the behavior found for the dimerization of 4. 27 In degassed solutions, both cis and trans dimers are formed readily, which suggests that intersystem crossing (step 3) occurs with some efficiency and that the triplet state dimerizes to form both cis and trans dimers. It is notable that the cis/trans ratio in degassed cyclohexane varies only slightly from that obtained in HAS.…”

Dynamics of Apolar Guest Solubilized in Bile Salt Micelles: Photochemistry of Acenaphthylene as a Probe to Understand the Supramolecular Characteristics of the Aggregates

“…Acenaphthylene (ACN) yields two dimers upon irradiation that are stereo isomers (Scheme 1) -the syn and the anti. 26,27 The proportion of syn and the anti dimers in the product mixture is dependent on three main factors, viz. multiplicity of excited state, concentration, and polarity of medium.…”

A Phosphorus Analogue of Acenaphthylene

“…A recent theoretical study concluded that the delocalization within the five‐membered ring is weak, which explains why the reactivity of the corresponding C=C double bond remains relatively high. Among the recent reactivity studies, we note an extensive investigation of its photochemical dimerization . The 1‐aza analogues are also known and have some interesting biological properties .…”

“…Among the recent reactivity studies, we note an extensive investigation of its photochemical dimerization. [3] The 1-aza analogues are also known and have some interesting biological properties. [4] To the best of our knowledge, no phosphorus analogue has ever been described, but some saturated acenaphthene analogues have been synthesized and used in asymmetric catalysis.…”