Self-Assembled Charge-Transfer Chiral π‑Materials: Stimuli-Responsive Circularly Polarized Luminescence and Chiroptical Photothermic Effects

Despite
significant achievements in the field of chiroptical organic
materials, the full utilization of both the excited state and ground
state chiroptical properties in a single supramolecular system is
still rarely disclosed. Here, we report that the rational combination
of the charge-transfer (CT) interaction with the spacer effect and
controlled protonation of π-histidine leads to chiroptical organic
π-materials with both circularly polarized luminescence (CPL)
and the supramolecular chirality-directed chiroptical photothermic
effect. Three pyrene-conjugated histidine derivatives with varied
acyl linkers (PyHis, PyC1His, and PyC3His) were designed to coassemble
with electron-deficient 1,2,4,5-tetracyanobenzene (TCNB), leading
to the formation of supramolecular CT complexes with intense orange
to red CPL depending on the linker length. The linker length also
affected the protonation-induced CPL responsiveness of the corresponding
CT assemblies. Upon protonation of the histidine moiety, PyC3His/TCNB
CT assemblies exhibited an inverted CPL signal, while PyHis/TCNB pairs
gave quenched CPL due to the disassembly. The protonation-controlled
PyC3His/TCNB CT assemblies at varied pH values showed different chiroptical
photothermic effects (CPEs) for the same incident chiral light despite
the molecular chirality of PyC3His remaining unchanged, supporting
an interesting supramolecular chirality-directed photothermic effect.