Highly Efficient Solid-State Intra-Track Polymerization of Ethynyl-Substituted Spirobifluorenes Triggered by Swift Heavy Ion Irradiations

Abstract

Acetylenes are the first monomer to polymerize by the energy deposited by ionizing radiations. Herein we report an extremely efficient solid state polymerization of ethynylsubstituted 9,9'-spirobi[9H-fluorene]s (SBFs) via a unique nano-fabrication technique referred to as Single Particle Trigged Linear Polymerization (STLiP) initiated by high energy charged particles. The resulted nanowires of polymerized/crosslinked SBFs show a gradual transformation from flexible to rigid rod-like with an increase in the reaction efficiency mediated by the ethynyl substitution. The overall efficiency of initiation/propagation/crosslinking reactions is remarkably high even in comparison with the primary yield of ionization events in the radiation chemical processes, marking up to G > 80 (100 eV)-1 , which is suggestive of efficient chain reactions in the propagation steps. The present results demonstrate efficient solid-state polymerization reactions, which are neither topochemical polymerization reactions nor acid/base catalyzed reactions, expand the versatility of STLiP technique to fabricate 1D nanomaterials based on a variety of organic compounds.

Porphyrin Nanowire Bundles for Efficient Photoconductivity, Photoemission, and Generation of Singlet Oxygens toward Photodynamic Therapy

“…According to the fact that the absorption spectra indicated the retention of the porphyrin ring after polymerization processes and Fourier transform infrared spectroscopy (FT-IR) spectra suggested the decrease of the stretching vibration of terminal alkyne groups, it is plausible that phenyl rings and/or its substituents (methyl, vinyl, alkynyl, and triethylsilyl groups) were most likely reacted in preference to the core parts and simultaneously have a great effect on the reaction efficiency of polymerization reactions. The obtained values of the averaged nanowire radii in Table S1 suggest that triple bonds in compounds 4 and 5 promote the polymerization reaction more than other substituents even though reaction intermediates were generated; silyl radicals in compound 6 were also generated. − Therefore, the high efficiencies in compounds 4 and 5 can be explained by the generation of vinyl radicals, reactive intermediates produced by attack of neutral radical species to the terminal alkyne . This behavior is presumed to be restricted for compound 6 because of the protection by triethylsilyl groups, resulting in the lower reaction efficiency.…”

“…5,10,15,20-Tetrakis­(3-methylphenyl)­porphyrin ( 2 ) was also used as a TPP analogue with high amorphous nature in films. TPPs carrying unsaturated carbon–carbon bonds such as vinyl ( 3 ) and ethynyl ( 4 , 5 , 6 ) groups instead of methyl groups at 3-positions were synthesized, as we expected the effect of functional groups for radiation-induced reactions based on the previous macromolecular and small molecular , examples. Initially, ion beam irradiation of the prepared films of 1 at a low fluence (∼10 8 –10 11 cm –2 ) was carried out to achieve initiation and propagation reactions of the TPP monomers that lead to the formation of one-dimensional organogels along the trajectories (ion tracks) of the respective particles (Figure ).…”

“…37−39 Therefore, the high efficiencies in compounds 4 and 5 can be explained by the generation of vinyl radicals, reactive intermediates produced by attack of neutral radical species to the terminal alkyne. 50 This behavior is presumed to be restricted for compound 6 because of the protection by triethylsilyl groups, resulting in the lower reaction efficiency. It should be noted that the reactivity to γ-rays for acetylene is reported to be higher than that for ethylene in the gas phase.…”