Photoinduced ElectronTransfer as a Probe for theFolding Behavior of Dimethylsilylene-Spaced Alternating Donor–AcceptorOligomers and Polymers.

A series of oligomers and polymers having dimethylsilylene-spacedalternating 4-aminostyrene donor and stilbene acceptor chromophores(two to one) are regioselectively synthesized, and the two donor chromophoresare separated by different bridges between two donors. Photophysicaltools have been used to examine the folding behavior of these copolymers.Both steady-state and time-resolved fluorescence spectroscopic measurementswere examined. The relative intensities (ICT/ILE) between emission from charge-separatedstate (CT emission) and local excited emission of acceptor chromophore(LE emission) increase with increasing number of repeating units,and reach a plateau, when the linkers between the two aminostyrenechromophores are trimethylene bridges. Replacements of these by dimethyleneor tetramethylene linker reduce the relative intensities of CT emissionof the polymers, owing to the different folding behavior of thesepolymers. The CT emission intensity of the polymer with rigid piperazinelinkers is much lower than that with trimethylene-bridged copolymerof the same degree of polymerization. Slight conformational changeof these polymers would lead to slight variation of the distance betweendonor and acceptor chromophores so that the nonadiabatic interactionsin the excited state between donor–acceptor pairs in theseoligomers and polymers would be perturbed by such change of conformations. [ABSTRACT FROM AUTHOR]