Endowing external, remote, and dynamic control to self-organized superstructures with
desired functionalities is a principal driving force in the bottom-up nanofabrication
of molecular devices. Light-driven chiral molecular switches or motors in liquid crystal
(LC) media capable of self-organizing into optically tunable one-dimensional (1D)
and three-dimensional (3D) superstructures represent such an elegant system. As a
consequence, photoresponsive cholesteric LCs (CLCs), i.e., self-organized 1D helical
superstructures, and LC blue phases (BPs), i.e., self-organized 3D periodic cubic
lattices, are emerging as a new generation of multifunctional supramolecular 1D and
3D photonic materials in their own right because of their fundamental academic interest
and technological significance. These smart stimuli-responsive materials can be facilely
fabricated from achiral LC hosts by the addition of a small amount of a light-driven
chiral molecular switch or motor. The photoresponsiveness of these materials is a
result of both molecular interaction and geometry changes in the chiral molecular
switch upon light irradiation. The doped photoresponsive CLCs undergo light-driven
pitch modulation and/or helix inversion, which has many applications in color filters,
polarizers, all-optical displays, optical lasers, sensors, energy-saving smart devices,
and so on. Recently, we have conceptualized and rationally synthesized different light-driven
chiral molecular switches that have very high helical twisting powers (HTPs) and exhibit
large changes in HTP in different states, thereby enabling wide phototunability of
the systems by the addition of very small amounts of the molecular switches into commercially
available achiral LCs. The light-driven chiral molecular switches are based on well-recognized
azobenzene, dithienylcyclopentene, and spirooxazine derivatives. We have demonstrated
high-resolution and lightweight photoaddressable displays without patterned electronics
on flexible substrates. The wide tunability of the HTP furnishes reflection colors
encompassing the whole visible spectrum and beyond in a reversible manner. Photomodulation
of the helical pitch of the CLCs has been achieved by UV, visible, and near-infrared
(NIR) light irradiation. NIR-light-induced red, green, and blue (RGB) reflections
have been leveraged only by varying the power density of the IR laser. Some chiral
switches are found to confer helix inversion to the cholesteric systems, which qualifies
the CLCs for applications where circularly polarized light is involved. Dynamic and
static primary RGB reflection colors have been achieved in a single film. LC BPs have
been fabricated and investigated in the context of self-organized 3D photonic band
gap (PBG) materials, and dynamic phototuning of the PBG over the visible region has
been achieved. Omnidirectional lasing and tuning of the laser emission wavelength
have also been attained in monodisperse photoresponsive CLC microshells fabricated
by a capillary-based microfluidic technique. This Account covers the research and
development in our laboratory starting from the design concepts and synthesis of photodynamic
chiral molecular switches to their applications in the fabrication of photoresponsive
CLCs and BPs. Potential and demonstrated practical applications of photoresponsive
CLCs, microshells, and BPs are discussed, and the Account concludes with a brief forecast
of what lies beyond the horizon in this rapidly expanding and fascinating field.