Effects of the Wavelength and the Matrix on the Photopolymerization of 2,5-Distyrylpyrazine and Its Related Compounds and on Their Photodepolymerization

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The solution photopolymerization of 2,5-distyrylpyrazine (DSP) and its related compounds with the general formula of Ar–CH=CH–Ar′–CH=CH–Ar, where Ar and Ar′ represent aryl and arylene groups respectively, have been investigated. All diolefines were converted in good yields into amorphous oligomers with cyclobutane in the main chain on the exclusive excitation of the monomer molecules, while, in the crystalline state, only DSP and 1,4-bis[β-pyridyl-(2)-vinyl] benzene are known to yield highly crystalline oligomers under the same light. All the oligomers were found to be photodepolymerized to the original monomers in the solution on the excitation of the terminal groups of these oligomers. In consequence, a photoreverse scheme has been demonstrated between the diolefinic monomer and the oligomer, depending on the excitation wavelength. Poly-DSP was photodepolymerized into the monomer in tifluoroacetic acid solution, while amorphous poly-DSP in film was readily photooxidized in the air under sunlight. From the photochemical behavior of DSP, oligo-DSP, and poly-DSP, it was found that chemically the same substance, oligo-DSP, behaved in three ways, photopolymerization, photodepolymerization and no photoreaction, according to the physical state. Such a matrix effect is discussed from the point of view of topochemical reaction.
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