Vinyl monomers bearing chromophore moieties and their polymers. VIII. synthesis and fluorescence behavior of a vinyloxy monomer having an electron-accepting chromophore moiety,p-((vinyloxy)methyl)benzonitrile, and its polymers

Abstract

A vinyloxy monomer having an electron-accepting chromophore moiety, p-((vinyloxy)methyl)benzonitrile (VOMBN), was synthesized by reaction of p-(hydroxymethyl)benzonitrile with ethyl vinyl ether (EVE) in the presence of mercuric acetate. VOMBN can easily be cationically homopolymerized and copolymerized with EVE by using Lewis acids such as boron trifluoride etherate (BF3 · OEt2) as a catalyst and radically copolymerized with maleic anhydride (MAn) using AIBN as an initiator. The fluorescence behaviors of VOMBN, its copolymer P(VOMBN-co-MAn), and its saturated model compound p-(ethoxymethyl)benzonitrile (EOMBN) were investigated in acetonitrile. It has been found that the fluorescence intensity of VOMBN is much lower than its copolymer and EOMBN at the same chromophore concentration. A fluorescence “structural self-quenching effect” (SSQE) is also observed for VOMBN as we have reported previously [Li, F. M.; Chen, S. J.; Li, Z. C.; Qiu, J. J Polym Sci Polym Chem 1996, 34, 1881]. This phenomenon has been attributed to the inter- and intramolecular charge transfer interaction between the electron-accepting cyanophenyl chromophore and the electron-donating vinyloxy group in the same molecule. The dependence of the fluorescence intensity of VOMBN on solvents of different viscosities is evidence that the SSQE of VOMBN mainly occurs intramolecularly. The fluorescence of EOMBN and P(VOMBN-co-MAn) was quenched by a series of electron-rich vinyloxy compounds which do not have chromophore moieties, such as dihydrofuran (2H-furan), dihydropyran (2H-pyran), furan, and EVE. It is observed that the higher the electron-donating ability of the quenchers, the greater the quenching efficiency. P(VOMBN) and the random copolymers of VOMBN with EVE show broader fluorescence spectra as compared to the alternating copolymer P(VOMBN-co-MAn). This indicates that there is a mutual interaction between the adjacent cyanophenyl groups in P(VOMBN) and P(VOMBN-co-EVE), whereas such an interaction does not exist for P(VOMBN-co-MAn) in which the cyanophenyl groups are isolated by the rigid succinic anhydride rings. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 179–187, 1999