Photoisomerization and Photooxygenation of 1,4-Diaryl-1,3-dienes in a Confined Space

Abstract

Geometric isomerization of light-activated olefins plays a significant role in biological events as well as in modern materials science applications. In these systems, the isomerization occurs in highly confined spaces, and concepts derived from solution investigations are only partially applicable. This study makes contributions in understanding the excited-state behavior of olefins in confined spaces by investigating the excited-state behavior of 1,4-diphneyl-13-butadiene (DPB) and 1,4-ditolyl-1,3-butadiene (DTB) encapsulated in a well-defined organic capsule made up of the octa acid (OA) host. Both of these dienes that exist in three isomeric forms (trans,trans; trans,cis; and cis,cis) formed 1:2 guest-host complexes with OA in aqueous borate buffer. Competition experiments monitored by (1)H NMR signals revealed that among the three isomers the cis,cis isomer of DPB and DTB formed the most stable complex with OA. Molecular modeling studies suggested that all six isomers of DPB and DTB preferred the cisoid conformation within the OA capsule. Irradiation (>280 nm) of the diene-OA complex (diene@OA2) resulted in geometric isomerization, and the photostationary state consisted of cis,trans isomer as major and cis,cis as minor products. The photostationary state could be enriched with the cis,cis isomer in yields close to 70% with proper cutoff filters because the cis,cis isomer absorbs at shorter wavelength than the other two isomers. Consistent with the MD simulation prediction that trans,trans-DPB and trans,trans-DTB existed in cisoid conformation within OA capsule, the generation of singlet oxygen in the presence of OA encapsulated DPB or DTB resulted in facile [4 + 2] addition between the diene and the singlet oxygen.

Control of reactivity and selectivity in isomerization and rearrangement reactions inside confined spaces

“…3). 10 As these dienes exist in three forms, the cis,cis -isomer, 4a , the cis,trans -isomer, 4b , and the trans,trans -isomer, 4c , the 4a isomer formed the more stable complex with OA 2 and underwent photo-isomerization reaction. In the confined space, the attained pss state consists of three isomeric forms, 4a–c , and differ with respect to the irradiation wavelength ( 4a under hν > 280 nm, 7%, 74%, and 17%, 4b under selective irradiation, hν > 340 nm, 77%, 21%, and 2% respectively).…”

Tuning the 1O2 Oxidation of a Phenol at the Air/Solid Interface of a Nanoparticle: Hydrophobic Surface Increases Oxophilicity

“…Interfacial strategies for selectivity in singlet oxygen ( 1 O 2 ) reactions could be developed, which do not rely on compartmentalization effects − and which also use air–water or air–solid interfaces. One relatively new approach is the delivery of 1 O 2 as a gas to the air–water interface in the presence of prenyl surfactants [(CH 3 ) 2 CCH­(CH 2 ) n SO 3 – Na + ( n = 4, 6, 8)], which results in higher “ene” hydroperoxide regioselectivity for secondary ROOH to tertiary ROOH, which is a relatively new approach .…”

“…CAB-O-Sil TS-720 fumed silica (surface-treated with polydimethylsiloxane, average diameter: 250 nm, surface area: 200 ± 25 m 2 /g) and S5505 hydrophilic fumed silica (surface area: average diameter: 250 nm, 200 ± 25 m 2 /g and ∼4 silanol groups/nm 2 ) was purchased from Composite Resources (Rock Hill, SC). Silica gel particles (average diameter: 60 μm) were purchased from SiliCycle Inc. Porous Vycor glass (PVG) was used (Corning 7930 from Advanced Glass and Ceramics, Holden, MA, density is 1.38 g/mm 3 ) and ground into microparticles with an average diameter of 69 μm. A Brucker Avance 400 MHz instrument was used to collect 1 H NMR data.…”