Photoinduced Charge Separation in Linked Donor-acceptor-chromophore Systems . Final Report


Book Description

A major experimental challenge in any study of intramolecular donor/acceptor (D/A) interactions is separating the variables which affect coupling. This is especially difficult when trying to evaluate the extent of through-bond superexchange. The systems of dinuclear complexes described below are unique in that the D/A connectivity can be varied without concomitant changes in D/A separation and relative orientation. Consequently, it has been possible to experimentally evaluate the effect of D/A linkage on coupling without introducing ambiguities from other structural changes. Furthermore, some of these systems are amenable to detailed theoretical treatment which allows quantitative comparisons between experiment and theory. A much more detailed picture of the D/A interaction is, thus, provided. Sections of this report include: unique structural aspects of[M(BBA)[sub 3]M[prime]] complexes; energy transfer in photoexcited[Ru(II)(BBA)[sub 3]Fe(II)][sup 4+] complexes; electrochemical investigation of[Fe(BBA)[sub 3]Fe][sup 4+]; optically-induced electron transfer in[Fe(II)(BBA)[sub 3]Fe(III)][sup 5+] mixed-valent complexes, where BBA=[alpha], [omega]-bisbipyridylalkane.




Photoinduced Charge Separation in Linked Donor-chromophore-acceptor Systems. Progress Report, September 1, 1993--May 31, 1993


Book Description

Focus has been mainly on preparation and characterization of triply bridged dinuclear complexes containing a tris-2-2'- bipyridineruthenium chromophore and a second tris-bipyridine metal complex which is to serve as electron donor or acceptor, and of linked RuL3-containing D-C-A complexes where D is a phenothiazine donor and A is a diquat type acceptor. (DLC).




Photoinduced Charge Separation in Linked Donor-chromophore-acceptor Systems


Book Description

Focus has been mainly on preparation and characterization of triply bridged dinuclear complexes containing a tris-2-2'- bipyridineruthenium chromophore and a second tris-bipyridine metal complex which is to serve as electron donor or acceptor, and of linked RuL[sub 3]-containing D-C-A complexes where D is a phenothiazine donor and A is a diquat type acceptor. (DLC).







Charge Separation in Covalently Bound and Self-assembled Donor Chromophore Acceptor Systems


Book Description

Covalently bound donor-acceptor species were synthesized in an attempt to extend the self assembly concept to a free chromophore system. A wide variety of DA species were studied, but ultimately triad-like behavior was not observed with free chromophore systems. Though attempts were made to control solvent effects, coulombic interactions, and DA flexibility, simple self assembled triad like behavior did not arise.










Photoinduced Charge Separation by Polymer-bound Chromophores


Book Description

This project has examined the photodynamic behavior of water-soluble polymers that have covalently linked hydrophobic chromophores spaced along the chains. These polymeric systems have been examined for photoinduced charge separation with electron-accepting ions having different total charge. Focus has been on the excited singlet (S1) state formed by laser flash absorption. The effects of pH and ionic strength -- factors that govern the conformational nature of the polymer in solution -- have been studied. A second major effort has been to study photoinduced redox processes involving excited states of water-soluble variants of anthracene and acridine. 27 refs., 16 figs., 2 tabs.




Photoinduced Electron Transfer in Ordered Polymers


Book Description

The present report gives a brief account of the following elements of work related to photochemical electron transfer themes: (1) the synthesis and Photochemical characterization of chromophore-bound peptides and amino acid model compounds based on the amino acids, tryptophan and the spacer residue, alanine (Ala); (2) the study of binding of cationic organic dyes to a peptide electrolyte, for which cooperative dye loading and helix formation is important; (3) the completion of work on a new series of acridinium chromophores that have rod-like'' arrangements of linked aryl rings for assembly of electron donor-acceptor systems that exhibit long lived charge separation; and (4) use of the modified form of the peptide, poly-L-histidine, as a template for sulfide oxidation.




Synthesis and Studies of AzaBODIPY Derived Donor-Acceptor Systems for Light Induced Charge Separation


Book Description

The efficiency and mechanism of electron- and energy transfer events occurring in both in natural and synthetic donor-acceptor systems depend on their distance, relative orientation, and the nature of the surrounding media. Fundamental knowledge gained from model studies is key in building efficient energy harvesting and optoelectronic devices. Faster charge separation and slower charge recombination in donor-acceptor systems is often sought out. In our continued effort to build donor-acceptor systems using near-IR sensitizers, in the present study, we report ground and excited state charge transfer in newly synthesized, directly linked, tetrads featuring bisdonor (donor = phenothiazine and ferrocene), BF2-chelated azadipyrromethane (azaBODIPY) and C60 entities. The tetrads synthesized using multi-step synthetic procedure revealed strong charge transfer interactions in the ground state involving the donor and azaBODIPY entities. The near-IR emitting azaBODIPY acted as a photosensitizing electron acceptor along with fullerene while the phenothiazine and ferrocene entities acted as electron donors. The triads (bisdonor-azaBODIPY) and tetrads revealed ultrafast photoinduced charge separation leading to D•+-azaBODIPY•--C60 and D•+-azaBODIPY-C60•- (D = phenothiazine or ferrocene) charge separated states from the femtosecond transient absorption spectral studies in both polar and nonpolar solvent media. The charge separated states populated the triplet excited state of azaBODIPY prior returning to the ground state.