Twisted intramolecular charge‐transfer state of trans‐3‐(N,N‐Dimethylamino)‐4'‐cyanostilbene: The C−C bond twisting

Abstract

Whether a twisted intramolecular charge‐transfer (TICT) state is formed is an important issue for understanding the fluorescence properties of a push‐pull organic dye. Here we report a position effect of the donor substituent on the TICT state formation of aminostilbenes: namely, trans‐3‐(N,N‐dimethylamino)‐4′‐cyanostilbene (mDCS) behaves differently from its TICT‐free para isomer DCS and forms a TICT state in acetonitrile (MeCN). The TICT state of mDCS also differs from that of many previously reported aminostilbenes by twisting a C−C bond instead of a C−N bond. In addition, among the ring‐bridged model compounds mDCS‐N, mDCS‐C1, and mDCS‐C2, we observed an unusual electronic effect of the ring‐bridging in mDCS‐C2 that mitigates the impact of the TICT state on the fluorescence properties. Both the C−C bond twisting in mDCS and the ring‐bridging electronic effect in mDCS‐C2 provide new insights into the TICT chemistry of aminostilbenes.