Photophysical properties of a series of polyisocyanides possessing porphyrin pendants (porphyrin polymers)
were investigated by steady state and transient spectroscopic methods. The B (Soret)-band of the free base
porphyrin polymers showed splitting indicating substantial exciton coupling in the porphyrin polymers due
to a face-to-face stacking conformation. On the other hand, the B-band of the zinc porphyrin polymers split
into four peaks indicating deviation from the strict face-to-face stacking conformation. The fluorescence
quantum yields of the porphyrin polymers were small compared with those of the corresponding monomers
and dimers. Furthermore, the fluorescence decay profiles of the porphyrin polymers deviated from single-exponential decay due to the structural heterogeneity of the polymers. It was revealed that the porphyrin
polymers showed transient absorption changes attributable to the exciton−exciton annihilation accompanying
structural change with the rate constant of (2−4) × 1010 s-1 regardless of the length of the polymer chain.
The quantum yields of the intersystem crossing of the polymers were smaller than those of monomers due to
the efficient exciton−exciton annihilation process in the singlet excited states. In the block copolymers of
zinc and free base porphyrins, energy transfer processes from zinc to free base porphyrin moieties were
confirmed by time-resolved fluorescence spectral and transient absorption spectral measurements. It became
clear that the energy transfer rates were almost independent of the sequence of the block copolymers, suggesting
that the rate-determining step of the energy transfer in the present block copolymers is the process at the
interface of zinc and free base porphyrins because of the sufficiently fast exciton migration in each block.
Multivalent carbohydrate photoaffinity probes were developed based on gold nanoparticles (AuNPs) to provide a streamlined approach toward identification of carbohydrate-binding proteins.
The photophysical properties of L-lysine-based polypeptides bearing porphyrin pendants were investigated. The intramolecular exciton-exciton annihilation resulting from the exciton migration among the porphyrin units deactivates the singlet excited state efficiently. It was revealed that the rate of the exciton migration depends on the polymerization degree.
Two are better than one: A new approach to selective photoaffinity labeling is described in which a bioactive probe is used in combination with its inactive analog as a scavenger of nonspecific proteins.
The synthesis and mechanistic studies of ortho-quinoid compounds have received much attention over the past decades. 1 2H-Benzothietes (1) are one of the important valence isomers of these orthoquinoid compounds (2), which have been especially interested in the reaction with dienophiles. 2 Benzooxetes (3) were prepared from benzofuran oxide derivatives, 3 which are labile and reverted to the quinone methides (4) and benzofuran epoxides upon prolonged storage (Scheme 1). 4 However, to our knowledge, there is no report on the synthesis of 2H-benzoselenete (5), which was postulated as an intermediate on the photolysis of 3-diazobenzo[b]-selenophen-2(3H)-one. 5 2H-Benzoselenete (5a) was found to be labile and revert to dibenzodiselenocin derivative, dimer of selenoquinone methide (6a).Recently, we have reported the reaction of thiones with benzynes, which provided a convenient method for the synthesis of 2H-benzothietes (1). 6 These results prompted us to investigate the possibility to synthesize 2H-benzoselenete (5) from selones (7) and benzyne. We herein report the first isolation of substituted benzoselenete derivatives, 5, in the reaction of selones, 7, with benzyne.A solution of 1,1,3,3-tetramethylindane-2-selone (7a) 7 and o-trimethylsilylphenyl trifluoromethanesulfonate (8) 8 in dichloromethane was treated with tetrabutylammonium fluoride in THF at room temperature, and then the solvent was removed in vacuo. Separation on silica gel chromatography and recrystallization from methanol led to the colorless crystals (mp 83-84 °C), which was found to be benzoselenete (5b) in 70% yield. The structure of 5b was determined by its 1 H NMR, 13 C NMR (Table 1).When 7a was treated with benzenediazonium 2-carboxylate (9) in refluxing benzene, compound 5b was obtained in 27% along with the rearranged product (10) in 7% yield (Scheme 2).
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