Pseudodimeric Complexes of an (18-Crown-6)stilbene with Styryl Dyes Containing an Ammonioalkyl Group: Synthesis, Structure, and Stereospecific [2 + 2] Cross-Photocycloaddition

Abstract

A new efficient method was proposed for the synthesis of (18-crown-6)­stilbene; the structure of the product was confirmed by X-ray diffraction analysis. In MeCN, this compound forms pseudodimeric complexes with N-(2-ammonioethyl)-4-styrylpyridinium and N-(3-ammoniopropyl)-4-styrylpyridinium diperchlorates via hydrogen bonding between the ammonium group and the crown ether oxygen atoms. The ammonioethyl derivative was synthesized for the first time. The stability constants and spectral characteristics of the complexes were measured by spectrophotometric and fluorescence titration. Photoirradiation of the pseudodimeric complex of (18-crown-6)­stilbene with the ammoniopropyl dye resulted in the stereospecific [2 + 2] cross-photocycloaddition reaction. The replacement of the stilbene moiety in the crown compound by a styrylpyridine moiety led to a 5-fold increase in the quantum yield of the photoprocess. The most probable cause for this effect is the presence of photoinduced electron transfer in (18-crown-6)­stilbene complexes. This assumption is confirmed by fluorescence lifetime spectroscopy and density functional theory calculations.

Polycationic Redox‐Active Cyclophanes with Integrated Electron‐Rich Diboron Units

“…An additional experiment, in which the possibility for a photoinduced [2+2] cycloaddition reaction between the two double bonds in [B 2 (hpp) 2 (L2) 2 ] 2+ was tested by irradiating a solution of the compound at different wavelengths, gave no clear results. [ 25 , 26 , 27 ]…”

“…An additional experiment, in which the possibility for a photoinduced [2 + 2] cycloaddition reaction between the two double bonds in [B 2 (hpp) 2 (L2) 2 ] 2 + was tested by irradiating a solution of the compound at different wavelengths, gave no clear results. [25][26][27] Finally, the salt [B 2 (hpp) 2 (L1 + Me) 2 ](OTf) 2 I 2 was obtained in 76 % isolated yield by reacting diborane 1 with two equivalents of (L1 + Me)I in CH 2 Cl 2 solution. The 11 B NMR spectrum shows a single signal at δ = 3.70 ppm.…”

Back electron transfer rates determine the photoreactivity of donor–acceptor stilbene complexes in a macrocyclic host

“…Directly accessing [2 + 2] chemistry from the CT state is generally considered improbable due to quick back electron transfer (BET) to the ground state following CT. [40][41][42][43] In fact, most studies of cross-[2 + 2] chemistry have viewed CT as a non-productive pathway. 3,[44][45][46] However, there is no fundamental reason why [2 + 2] chemistry cannot be accessed by the radical ions produced by CT, though such reactivity might be accessible only to a small number of electronically "matched" substrates in which [2 + 2] can compete with BET.…”

Photoreactivity of donor-acceptor stilbene complexes in a macrocyclic host

“…[37][38][39][40] In fact, most studies of cross-[2+2] chemistry have viewed CT as a nonproductive pathway. 3,[41][42][43] However, it should be fundamentally possible to directly access [2+2] reactivity from the radical ions produced by CT absorption, and host-guest complexes offer an ideal platform to investigate such CT-initiated chemistry by providing modular access to well-defined donor-acceptor complexes. 34 In this work, we investigated a series of donor-acceptor host-guest ternary complexes between stilbenes and CB [8] and discovered that CT reactivity is highly sensitive to the structure of the donor stilbene.…”