New functional polymers prepared by ring-opening metathesis polymerization: Study of the quenching of luminescence of pyrene end groups by ferrocene or phenothiazine centers in the polymers

Emission from pyrene end-capped redox polymers is quenched relative to emission from 1-vinylpyrene, a structural model for the end group in the polymer. The redox polymers were prepared by ring-opening metathesis polymerization (ROMP) of norbornene derivatives containing ferrocene or phenothiazine, using catalysts of the type Mo(CH-t-Bu)(NAr)(O-t-Bu)₂ (Ar = 2,6-diisopropylphenyl). The pyrene group was introduced by reaction of the living polymer with 1-pyrenecarboxaldehyde, thus producing polymers that are derivatives of 1-vinylpyrene. A ferrocene-containing homopolymer was prepared with 12 equiv of a ferrocene-containing monomer, followed by capping with pyrene, (1)₁₂-pyrene, where pyrene emission is quenched by a factor of 30. Two phenothiazine-containing polymers were studied; a homopolymer prepared from 10 equiv of a phenothiazine-containing monomer followed by capping with pyrene, (2)₁₀-pyrene, and a block copolymer formed from 10 equiv of a phenothiazine monomer, then 70 equiv of norbornene, (NBE), followed by capping with pyrene, (2)₁₀(NBE)₇₀-pyrene. In these polymers pyrene emission is quenched by a factor of 110 and 7, respectively. The quenching is proposed to occur via electron transfer from phenothiazine to the excited singlet state of pyrene and, depending on the structure of the polymer, by the formation of an exciplex with phenothiazine. (2)₁₀-pyrene has a broad, featureless emission arising from excitation of the pyrene chromophore whose maximum is shifted >6100 cm^-1 to lower energy from the singlet energy of 1-vinylpyrene that is assigned to be emission from a pyrene/phenothiazine exciplex. The block copolymer (2)₁₀(NBE)₇₀-pyrene does not display this low-energy emission, nor do solutions containing the separate species 1-vinylpyrene and either N-methylphenothiazine or the phenothiazine-containing monomer, 2.