Long lived charge separated states in vinylbenzonitrile substituted derivatives of pyrene and anthracene

The present study investigates the photophysical properties of two highly conjugated pyrene and anthracene derivatives viz (E)-4-(2-(pyren-1-yl) vinyl) benzonitrile (PyCN) and (E)-4-(2-(anthracen-9-yl) vinyl) benzonitrile (AnCN) in the presence and absence of electron donors such as N,N-diethylaniline (DEA) and N,N-diphenylamine (DPA). The observed rates of back electron transfer (BET) in the case of PyCN-DEA and AnCN-DEA are 1.3 × 105 and 4.8 × 104 s−1, respectively, which are 3–4 orders of magnitude lower compared to the well-known pyrene–amine and anthracene–amine systems. Mechanistic investigations indicate that the donor-acceptor systems undergo different pathways in presence of tertiary and the secondary amine. The results indicate that the design strategy is highly efficient in reducing the rate of back electron transfer, which results in long lived charge-separated excited states.