Synthesis of Chiral Donor-Acceptor Dyes to Study Electron Transfer Across a Chiral Bridge.

Chiral organic dyes comprising a donor (D), spacer (S), primary acceptor (A1), chiral bridge (B(S)), and final acceptor/radical (A2)/(R) have been synthesized and fully characterized. The goal behind this synthetic pursuit is to study whether the chiral dyes can impart a chiral-induced spin selectivity (CISS) spin-filtering effect during an intramolecular charge-transfer (CT) process. Additionally, appending a stable free radical (SFR) allows the study of how an unpaired spin influences the CT state. The dyes are reported to vary in the position of (A1) with respect to (B(S)). Two series of dyes have been synthesized: one series incorporates (A1) before (B(S)) and the second series places (A1) after (B(S)). In the case where (A1) is before (B(S)), CT is observed between (D) and (A1), but the CT state does not transverse over the chiral bridge to the final (A2)/(R) termini. However, when (A1) is placed after (B(S)), CT over or through the bridge occurs. Computations support the experimental data, which indicate that it is necessary to have (A1) located after (B(S)) to achieve CT over the chiral bridge. Hence, the second set of dyes are optimal candidates to explore intramolecular CISS.