Influence of π-conjugation structural changes on intramolecular charge transfer and photoinduced electron transfer in donor-π-acceptor dyads

The influence of π-conjugation structural changes on photoinduced electron transfer (PET) and intramolecular charge transfer (ICT) processes in π-conjugated donor (D)-acceptor (A) dyads (D-π-A) was investigated. Three types of D-π-A dyads were prepared through the modification of the structure of their π-conjugated linker, including D-π-A (1) and D-π -A (2) having a twisted π-conjugation, and D-π-Si-π-A (3) with a π-conjugation severed by a Si-atom. In these dyads, carbazole (Cz) and oxadiazole (Oz) moieties act as an electron donor and acceptor, respectively. The emission maxima of dyads 1 and 3 red-shifted with the increase in polarity, which could be attributed to the ICT process. The fluorescence lifetimes of dyads 1 and 3 were 2.64 and 4.29 ns in CH Cl , respectively. In contrast, dyad 2 showed dual emission at 350 and 470 nm in CH Cl . The emission of dyad 2 at 380 nm corresponded to the monomer fluorescence in the locally excited state. Moreover, the emission at 470 nm increased simultaneously with the diminishing of the fluorescence at 380 nm. This emission band can be assigned as the intramolecular exciplex emission, and showed a strong solvatochromic shift. The low emission quantum yield (