The binding of pseudoisocyanine (PIC+) to the polyelectrolyte poly(methacry1ic acid) (PMAA) has profound effects on the photophysical and photochemical properties of this prototypical cyanine dye. The hydrophobic dye was bound in the microdomain of the compact conformation of the polymer in its (uncharged, "hypercoiled") acid form at pH < 4.0 in water. Under these conditions, the fluorescence quantum yield for PIC+ was increased 600-fold and its lifetime is extended to 2.7 ns. The dye triplet state observed by flash photolysis provided a very long-lived phototransient (Amx = 640 nm, 50-100-ps decay time). Electron-transfer quenching was investigated using the oxidant tetranitromethane (TNM) which provided thesemioxidized dye radical intermediate (440-nm transient) on cobinding within PMAA hypercoils. The dye was also bound to a covalently modified form of PMAA in which polymer chains were end-labeled with 9-methylanthracene moieties. Electron transfer between anthracene chromophores and PIC+ within the polymer domain was observed.

For a series of alanine-based peptides having 1-3 amino acid residues as spacers, the chromophore, pyrenesulfonyl (Pyr), has been attached at the N-terminus and an electron donor, dimethyl-1,4-benzenediamine (DMPD), covalently bound at the C-terminus. Evidence for an intramolecular charge-transfer interaction involving the electron donor and acceptor groups has been obtained from absorption spectra. Intramolecular electron transfer involving the end groups, Pyr (electron acceptor) and DMPD (electron donor) has been confirmed by ultrafast pump-probe methods. The radical-ion pair states that are generated on Ti/sapphire laser excitation at 400 nm decay in the picosecond to nanosecond time domain and generally show multiexponential decay kinetics. These rates of charge recombination are among the fastest yet observed involving electron transfer between terminal groups for peptide oligomers. The falloff of rate constants for ion pair recombination is irregular in terms of the through-bond distance that separates Pyr and DMPD groups for the various peptide links; i.e., back electron transfer remains fast for the tripeptide, Pyr-Ala-Ala-Ala-DMPD, despite an average through-bond distance between photoactive groups that reaches 18 Å. Molecular modeling studies show that the peptides are free to adopt conformations in essentially random fashion, without showing evidence for long range ordering of the peptide chain.

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The electron-transfer photochemistry of the covalent derivatives of the dye eosin, in which the xanthene dye is covalently attached to the amino acid L-tryptophan via the thiohydantoin derivative, the tryptophan dipeptide, and an ethyl ester derivative, has been investigated. The singlet excited state of the dye is significantly quenched on attachment of the aromatic amino acid residue. Dye triplet states are also intercepted through intramolecular interaction of excited dye and amino acid pendants. Flash photolysis experiments verify that this interaction involves electron transfer from the indole side chains of tryptophan. Rate constants for electron transfer are discussed in terms of the distance relationships for the eosin chromophore and aromatic redox sites on peptide derivatives, the pathway for u--'IT through-bond interaction between redox sites, and the multiplicity and state of protonation for electron-transfer intermediates. Selected electron-transfer photoreactions were studied under conditions of binding of the peptide derivatives in a high molecular weight, water-soluble, globular polymer, poly(viny1-2-pyrrolidinone).

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