The poly(p-phenylezthynylene) molecules, PI-PIII, synthesized by a palladium-catalyzed cross-coupling reaction of diiodobenzene derivatives and derivatives of 1,4-diethynylbenzene, are highly luminescent materials. The polymers are soluble by virtue of the -OC16H33 groups introduced on the aromatic rings and by controlling their molecular weight. The fluorescent quantum yields are between 0.35 and 0.40 depending on the material. The excited-state Lifetimes of the polymers are 1-2 ns, slightly shorter than that of the model compound, 1,4-diphenylethynyl-2,5-dibutoxybenzene, which has a lifetime of 3 ns. Incorporation of anthracene, coupled at the 9,10-positions by using 9,10-bibromoanthracene, into the polymer backbone decreases the quantum yield to between 0.05 and 0.27 depending on the anthracene content. In addition, low-energy electronic transitions and longer wavelength emission bands associated with the anthracene group are produced. The polymers harvest optical energy and transfer it to the anthracene resulting in emission from this chromophore. In the case where only terminal anthracene units, introduced by using 9-bromo-10-phenylethynylanthracene, are present, the process is very efficient with >95% of the energy being transferred to the end groups.

Energy and electron transfer processes at the surface-electrolyte interface were studied using monolayers of Re(I) carbonyl complexes chemically immobilized on gold surfaces. Cyclic voltammetry, Chromoamperometry, grazing-angle specular-reflectance infrared spectroscopy and fluorescence spectroscopy were used to characterize the complexes and explore the rates of energy transfer to the gold surfaces.

Like the metallocenes themselves, metallocene-based polymers exhibit near-UV (280-370 nm) charge-transfer-to-solvent (CTTS) absorption in the presence of CCl4, CHCl3, CH2Cl2, CBr4, and CHBr3. The photoelectrochemistry of charge transfer complexes of two ferrocene-containing polymers and one cobaltocene-containing polymer has been studied. The polymers are poly(2-ferrocenylethyl methacrylate), poly(3-(octamethylferrocenyl)propyl methacrylate), and poly(1,1'-bis[((3-(triethoxysilyl)propyl)amino)carbonyl]cobaltocene). Photoexcitation of metallocenes and metallocene-based polymers in the presence of many halocarbons yields oxidation of the metallocene and reduction of the halocarbon. When the metallocene-based polymer is confined to the surface of an electrode that is held at a potential negative of the formal potential of the metallocene, near-UV excitation results in sustained cathodic current in electrolyte solutions containing halocarbons. The wavelength, acceptor, and potential dependences are in accord with a sustained current that is due to a metallocene-to-halocarbon CTTS absorption where the photoprocess results in the reduction of the halocarbon at an electrode potential significantly positive of where electrochemical reduction occurs in the dark. The octamethylferrocene-based system shows a more negative potential onset and a longer wavelength offset of photocurrent than the simple ferrocene-based system, consistent with the electron-releasing nature of the methyl substituents. The onset of photocurrent in the cobaltocene-based system occurs at the most negative potential of the three, consistent with the cobaltocene-based system having the most negative formal potential of the metallocenes studied.

Derivatives of (eta5-C5H5)Mn(CO)3 attached to SiO2, Si, or Au surfaces undergo photoreactions that allow the surface to be tailored in a rational manner. Photosubstitution of functionalized phosphines for CO occurs on all substrates, although the scope of the reaction is more limited for the surface-confined species than for the analogous complexes in solution. Flat surfaces modified with the derivatives of (eta5-C5H5)Mn(CO)3 can be patterned photochemically, because no thermal CO substitution occurs.

Polymers play an important role in the field of photochemical applications and photo-electrical applications. In this article we will focus on some typical examples of using polymers in modern technologies taken from the field of photoconductivity, photochemistry, and nonlinear optical applications. The latter field points towards a new direction, namely using polymers for optoelectronic applications. It will be shown that the technical material requirements for optoelectronic applications are rather different from the requirements which have to be fulfilled for conventional photochemistry and photophysics. It will be more and more the solid-state and semiconductor aspects which will enter the field of research, and developement and these new aspects will be as important as the aspects of conventional polymer physics. Special Photochemical Reactions in Polymers Light-Induced Structural Changes of Polymers Light-Induced Conductivity Changes of Polymers (Photoconductivity) Light-Driven Nonlinear Processes in Polymers Current-Driven Luminescence Properties of Polymers (Electroluminescence). Along with the above photonic properties there is a whole series of applications which are based on the various photoreactions as summarized above. These applications are: Photochemistry: Photo-lithography, Printing Techniques, Photoresist Applications, Optical Memories, etc. Structural Changes: Holographic Applications, Optical Memories, etc.

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 I-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 I-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.

Redox-active polymers and block polymers containing terminal groups for covalent attachment to surfaces have been prepared and characterized. Ferrocene- and phenothiazine-based redox-active polymers were prepared by ring-opening metathesis polymerization (ROMP) using Mo initiators of the type Mo(CHR)(NAr)(O-t-Bu)2 (R = tert-butyl or ferrocenyl, Ar = 2,6-diisopropylphenyl). The functional end groups introduced for surface attachment chemistry were Si(OEt)3, pyridyl, bromobenzyl, and pyrenyl derivatives. Polymers containing Si(OEt)3 were successfully used to derivatize Pt, In2(Sn)O3, and n-Si electrodes, whereas analogues of those same polymers lacking Si(OEt)3 groups do not bind to these surfaces. Polymers terminated with pyridyl or bromobenzyl groups, introduced in the capping reaction using the appropriate aldehydes, react with electrodes pretreated with benzyl chloride or pyridine groups, respectively, to give polymer-derivatized surfaces. Pyrene-capped polymers were made in an attempt to bind the polymers to carbon electrodes via selective pyrene adsorption. However, the polymer itself strongly adsorbs, precluding a specific role for the pyrene group. On the basis of the surface coverage found for the redox-active groups (approximately 1 X 10(-10) mol cm-2) and polymers (approximately 8 X 10(-12) mol cm-2) at the electrode surfaces, bound polymer chains hinder the access of unbound polymers to portions of the surface, thereby yielding a lower density of bound polymer than would be expected were the chain to extend away from the electrode surface.

Mo(CH-t-Bu)(NAr)(O-t-BU)2 (1a) in THf/0.1 M [n-Bu4N]AsF6 is not oxidized at potentials up to 1.0 V and undergoes a reversible, one electron reduction at -2.16 V vs SCE at a Pt electrode. An analogous intiator containing a ferrocenylmethylidene ligand (1b) can be synthesized by treating la with vinylferrocene. Redox-active derivatives of norbornene, containing ferrocene (2) or phenothiazine (3), were prepared and polymerized by 1a or 1b to give living block copolymers containing the ring-opened norbornene derivatives. The living polymer was cleaved from the metal in a Wittig-like reaction with pivaldehyde, trimethylsilylbenzaldehyde, or octamethylferrocenecarboxaldehyde. Polydispersities for the longer block copolymers containing up to approximately 80 monomer units were found to be as low as 1.05 by GPC. In one case the polydispersity of a homopolymer made from the ferrocene-containing monomer was determined by FD-mass spectroscopy to be 1.06. DSC studies suggest that microphase formation occurs in the block copolymers, even in the case of relatively low molecular weight materials. Solution voltammetric studies of homo and block copolymers showed that the redox centers were electrochemically independent and that all centers exchanged electrons with the electrode. Neutral polymers became insoluble upon oxidation to a polycation, yielding an adsorbed polymer layer on the electrode that could then be cathodically stripped. This oxidative deposition process depended on the electrolyte and the polymer molecular weight but also could be controlled by the size of a nonelectroactive block in the block copolymers. Problems resulting from precipitation of the redox polymers could be circumvented by employing normal pulse voltammetry. Polymers containing redox centers in both end groups as well as in the polymer chain itself have been prepared and their nature confirmed in electrochemical studies.

The controlled ring-opening metathesis polymerization of 7,8-bis(trifluoromethyl)tricyclo[4.2.2.02,5]-deca-3,7,9-triene has been employed to prepare soluble polymers of low polydispersity that are precursors to polyenes. Films of these precursor polymers have been cast from solution onto platinum microelectrode arrays and have been heated to form films of polyacetylene in the molecular weight range 400-6500. These films have been characterized by in situ measurements of conductivity as a function of electrochemical potential in liquid SO2/electrolyte. The results show a steady increase in conductivity with average chain length for samples with chain lengths in the range 11-60 double bonds, above which conductivity levels off as chain length continues to increase. All samples exhibit a finite potential window of conductivity which increases in width in the range 11-60 double bonds and does not change further with increasing chain length.

Microelectrode arrays, consisting of six or eight individually addressable Au or Pt microelectrodes about 2 μm wide, 50 μm long, and 0.1 μm thick separated by about 2 μm on a Si3N4 substrate, can be modified by immersion into a solution containing molecules having thiol, dithiocarbamate, or disulfide functional groups. The functional groups yield selective modification of the Au or Pt, not the Si3N4, with about one monolayer of molecular reagents. Electrochemical and Auger electron spectroscopy (AES) data are summarized to illustrate that the dithiocarbamate functional group can be used to link redox active molecules to Au or Pt surfaces. Results are presented to illustrate that secondary ion mass spectrometry (SIMS) can be used to characterize organic monolayers on the microelectrodes. Preliminary findings are presented showing the esters of lipoic acid, a five-membered cyclic disulfide, will selectively modify Au surfaces versus Si3N4, and the cyclic disulfide will kinetically compete with a linear disulfide for sites on a Au surfaces. In a competition with the linear disulfide, the cyclic disulfide is at least ten times more reactive towards Au. Overall, the studies define classes of experiments needed to develop rational approaches to the modification of surfaces using spontaneous self-assembly methods by taking advantage of selective surface coordination chemistry of molecules having appropriate functional groups.

New kinds of microelectrochemical sensors are described involving two redox active molecules immobilized onto a microelectrode. One redox species is chemically insensitive with respect to variation in E1/2, e.g. a ferrocene derivative, and serves as an internal reference in a linear sweep voltammogram. The second species is chemically sensitive, e.g. a pH sensitive quinone or a CO sensitive ferraazetine derivative, which has an E1/2 that varies with the changes in the chemical environment. A linear sweep voltammogram thus shows two waves, one for the reference molecule and one for the indicator molecule. The shift for the indicator wave along the potential or current axis provides a method for analyte detection. Surface derivatization, proof-of-structure, and proof-of-concept sensor functions are demonstrated.