We report a transparent, fluorescent gel assembled from a cyanostilbene-containing material (compound 1), which incorporates bulky and flexible spacers via an amide group and exhibits aggregation-induced enhanced emission (AIEE). The photoinduced morphological change (gel-to-sol) upon the photoisomerization of 1 was successfully demonstrated, which was accompanied by a fluorescence color switching from the aggregate emission (490 nm) to the monomer emission (465 nm). It is notable that the photoisomerization of the cyanostilbene moiety in our innovative system induces both the gel-to-sol transition and the fluorescence color.

　We report herein a new class of piezochromic luminescence (PCL) material with an acid stimulus response based on a donor (D)–acceptor (A)–donor (D) molecular triad, m-BHHDCS (1), synthesized via a rational design strategy. Acid-responsive harmane derivatives were rationally introduced into the unique D–A–D platform to obtain dual-stimuli responsive properties, i.e. acidochromic and piezochromic behaviors. Upon exposure to mechanical force and/or acid treatment, the pristine powders of 1 showed rapid and instant fluorescence turn-on with discernible intensity (Φ1B = 9% and Φ1C = 5%, respectively). In order to test more practical applications, we utilized light as a stimulus source using a photo-acid generator (PAG) instead of acid, and thus successfully demonstrated an intriguing optical recording medium orthogonally activated by mechanical force and light. Moreover, based on the in-depth combined experimental and computational studies, we could conclude that the dual-stimuli responsive properties of 1 originated from a structurally controlled photo-induced electron transfer (PET) process in the molecular assemblies, that is inhibited by mechanical force and acid. Mechanical force destroys the characteristic stacked structure, so that the ultrafast PET is inhibited and fluorescence is recovered. In contrast, acid covalently binds to the harmane appendages in the specific stacked arrangement of 1, which efficiently blocks PET. We believe that this system will inspire the development of a new class of smart PCL materials, and furthermore provide important insights into solid-state emission and stimuli-response behaviors.

　Enhanced DC conductivity and photoconductivity of cationic carbazole tethered deoxyribonucleic acid (Cz-DNA) in film devices is achieved by incorporating mobility enhancers. An anthracene-based organic semiconductor (namely 4HPA-Ant) and the inorganic semiconductor cadmium sulfide (CdS) multipod nanocrystal (NC) were used as the mobility enhancers. Space charge limited current (SCLC) experiments show that hole mobility in CdS:Cz-DNA composite film is improved significantly, by about an order of magnitude, compared to the Cz-DNA film. Similarly, the DC conductivity of the composite film is slightly enhanced by 4HPA-Ant. The photoconductivity is also improved in the Cz-DNA composite, with both 4HPA-Ant and CdS multipod NCs. The enhancement in photocurrent is by more than an order of magnitude, as demonstrated by current–voltage (I–V) characterization using DNA composite photodetectors.

　Nanochemistry and nanomaterials provide numerous opportunities for a new generation of photovoltaics with high solar energy conversion efficiencies at low fabrication cost. Quantum-confined nanomaterials and polymer–inorganic nanocomposites can be tailored to harvest sun light over a broad range of the spectrum, while plasmonic structures offer effective ways to reduce the thickness of light-absorbing layers. Multiple exciton generation, singlet exciton fission, photon down-conversion, and photon up-conversion realized in nanostructures, create significant interest for harvesting underutilized ultraviolet and currently unutilized infrared photons. Nanochemical interface engineering of nanoparticle surfaces and junction-interfaces enable enhanced charge separation and collection. In this review, we survey these recent advances employed to introduce new concepts for improving the solar energy conversion efficiency, and reduce the device fabrication cost in photovoltaic technologies. The review concludes with a summary of contributions already made by nanochemistry. It then describes the challenges and opportunities in photovoltaics where the chemical community can play a vital role.