Principle of the PCT chemically driven luminescent molecular switch based on the donor-spacer-acceptor architecture. Binding of cationic trigger to the donor (green) moiety results in the hypsochromic shift of absorption (emission) band (a), and binding of the same trigger to the acceptor moiety (red) results in bathochromic shift of the corresponding transition (b). The multireceptor system may exhibit both bathochromic and hypsochromic shifts upon binding different trigger ions (c), which results in a multistate molecular switch.
