Synthesis, Structure, Photoluminescence and Photoreactivity of 2,3‐Diphenyl‐4‐neopentyl‐1‐silacyclobut‐2‐enes

Abstract

A series of six 2,3-diphenyl-4-neopentyl-1-silacyclobut-2-enes with different 1,1-substituents has been prepared and characterized by single-crystal X-ray crystallography. These compounds possess a cis-stilbene-like chromophore involving also the four-membered ring, and exhibit a photophysical behavior similar to that of previously reported 1,2-diphenyl-cycloalkenes. This chromophore system is confirmed by a theoretical investigation of the electronic structure and excitation spectra. The absorption and photoluminescence of selected derivatives were studied in solution, as solid powder samples, and in doped-polymer thin films. In well-dissolved solution, the silacyclobutenes show only very weak fluorescence emission (quantum yield approximately 0.1%), due to competition with photochemical and non-radiative photophysical relaxation. When the solubility is degraded in a poor (aqueous) solvent, the formation of nanoscale aggregates leads to a significant enhancement factor in the emission intensity, due to the suppression of the photoreactivity in the more rigid molecular environment, although the quantum yield still remains below a few percent. In the solid-state, however, photoreactivity is completely suppressed leading to fluorescence quantum efficiencies of 8-23% depending on the 1,1-substituents, which demonstrates these compounds' potential as chromophores for condensed-phase luminescence applications. Two dominant competing photochemical reactions have been identified in solution (for excitation in the lowest-energy absorption band, >260 nm), which are analogous to related (sila-)cyclobutenes and stilbenoids. The first involves ring-opening due to cleavage of the 1,4-Si-C bond to form metastable silabutadienes, which was confirmed by isolating the stereospecifically formed allylsilane which results from a secondary reaction with trapping agents such as methanol or water. The second photochemical reaction involves ring closure of the 2,3-diphenyl substructure to form a dihydrophenanthrene analogue, which was confirmed by isolating the phenanthrene derivative that results following subsequent hydrogen abstraction in the presence of oxygen. Measurements of the silacyclobutenes in doped-polymer thin films reveal a spectroscopic behavior ranging from that in solution to the nano-aggregate case as the silacyclobutene dopant concentration is increased.

Building up Strain in One Step: Synthesis of an Edge‐Fused Double Silacyclobutene from an Extensively Trichlorosilylated Butadiene Dianion

“…Moreover, Auner's and our works provide extremely rare protocols for the synthesis of 1,1‐dichlorosilacyclobutenes, which offer a multitude of options for subsequent Si derivatization . Appropriately derivatized silacyclobutenes can be introduced into the polymer main chains of polysilanes, carbosilanes, and siloxanes by taking advantage of the functional groups at the Si centers or by performing ring‐opening polymerization reactions; silacyclobutenes are also promising building blocks for organic–inorganic optoelectronic materials …”

“…[31,34,[36][37][38][39] Appropriately derivatized silacyclobutenes can be introduced into the polymer main chains of polysilanes,c arbosilanes,a nd siloxanes by taking advantage of the functional groups at the Si centers or by performing ring-opening polymerization reactions;silacyclobutenes are also promising building blocks for organic-inorganic optoelectronic materials. [27,30,[37][38][39][40][41] Thes ix-membered bicyclic scaffold of 4 has little precedence in the literature:Aclose relative G (Figure 3) stems from Weidenbruchsgroup and can be regarded as asterically protected, desilylated version of 4.Molecule G was prepared from the photogenerated silylene [Si(tBu) 2 ]and the 1,3-diyne tBuCCÀCCtBu via the rearrangement of ab is(silirene) intermediate. [42] Isomers G' ' and G' '' ' have been assessed by experimental and/or theoretical means.…”

Substituent Effects in Thermal Reactions of a Silene with Silyl-Substituted Alkynes: A Theoretical Study

“…It has been reported that some of the silacyclobutene derivatives show interesting optical properties, which may be used as functional materials, such as organic electroluminescent devices. , …”

DFT study of Si/Ge conjugated systems

“… 115. Depending on the substituents, synthesized 1-R can have 8-23% fluorescence quantum efficiency in solid form.…”