Molecular materials with concomitant light-emissive and semiconducting properties have received increasing attention in recent years. Such dual functional materials ensure the development of multifunctional devices (e.g., organic light-emitting transistors) and the emergence of new technologies. However, owing to the fact that intermolecular interactions and dense packing have opposite effects on photoluminescence and charge-carrier mobility, it is still rather challenging to rationally design high-performance molecular materials that exhibit both semiconducting and light-emissive properties. In fact, only a limited number of such dual functional materials are available, and most of their performances need to be further improved. In this concept article we discuss the design strategies and perspectives of this challenging area with the introduction of representative examples of such dual functional materials reported in recent years.

In this paper, a new cruciform donor–acceptor molecule 2,2'-((5,5'-(3,7-dicyano-2,6-bis(dihexylamino)benzo[1,2-b:4,5-b']difuran-4,8-diyl)bis(thiophene-5,2-diyl))bis (methanylylidene))dimalononitrile (BDFTM) is reported. The compound exhibits both remarkable solid-state red emission and p-type semiconducting behavior. The dual functions of BDFTM are ascribed to its unique crystal structure, in which there are no intermolecular face-to-face π–π interactions, but the molecules are associated by intermolecular CN…π and H-bonding interactions. Firstly, BDFTM exhibits aggregation-induced emission; that is, in solution, it is almost non-emissive but becomes significantly fluorescent after aggregation. The emission quantum yield and average lifetime are measured to be 0.16 and 2.02 ns, respectively. Crystalline microrods and microplates of BDFTM show typical optical waveguiding behaviors with a rather low optical loss coefficient. Moreover, microplates of BDFTM can function as planar optical microcavities which can confine the emitted photons by the reflection at the crystal edges. Thin films show an air-stable p-type semiconducting property with a hole mobility up to 0.0015 cm²V⁻¹s⁻¹. Notably, an OFET with a thin film of BDFTM is successfully utilized for highly sensitive and selective detection of H₂S gas (down to ppb levels).

Two-dimensional covalent organic frameworks (2D COFs) provide a unique platform for the molecular design of electronic and optoelectronic materials. Here, the synthesis and characterization of an electroactive COF containing the well-known tetrathiafulvalene (TTF) unit is reported. The TTF-COF crystallizes into 2D sheets with an eclipsed AA stacking motif, and shows high thermal stability and permanent porosity. The presence of TTF units endows the TTF-COF with electron-donating ability, which is characterized by cyclic voltammetry. In addition, the open frameworks of TTF-COF are amenable to doping with electron acceptors (e.g., iodine), and the conductivity of TTF-COF bulk samples can be improved by doping. Our results open up a reliable route for the preparation of well-ordered conjugated TTF polymers, which hold great potential for applications in fields from molecular electronics to energy storage.

Smart molecular probes and flexible methods are attracting remarkable interest for the visualization of cancer-related biological and chemical events. In this work, a new fluorescence turn-on probe with dual-recognition characteristics for the specific imaging of cancer cells is reported. This new bioprobe is rationally designed by linking tetraphenylethylene (TPE), an aggregation-induced emission (AIE) fluorophore, with the small peptide IHGHHIISVG (referred to as AP2H), a targeting ligand to the broad-spectrum cancer-related protein LAPTM4B. The binding of the probe TPE-AP2H with the target, both in solution and at the cellular level, switches on the fluorescence of TPE because of the inhibition of internal rotations within the TPE framework. Accordingly, this bioprobe allows the real-time monitoring and subcellular localization of LAPTM4B in cancer cells, with a very high target-to-background ratio for the imaging. Furthermore, brighter fluorescence images are detected after incubation of TPE-AP2H with tumor cells at lower pH values. Thus, this new bioprobe is more advantageous because it can simultaneously target the LAPTM4B protein and sense the characteristic low-pH environment of tumor cells. In addition, TPE-AP2H displays high photostability and low cytotoxicity. Therefore, this new bioprobe is promising for the more accurate and reliable imaging of tumor markers in live cancer cells.

We report a method for the rapid and efficient identification of bacteria making use of five probes having fluorescent characteristics (F-array) and subsequent statistical analysis. Eight kinds of bacteria, including normal and multidrug-resistant bacteria, are differentiated successfully. Our easy-to-perform and time-saving method consists of mixing bacteria and probes, recording fluorescent intensity data by automated flow cytometry, and statistical analysis. No washing steps are required in order to identify the different bacteria simultaneously.

The synthesis of a new tetrathiafulvalene derivative with an electron-withdrawing benzothiadiazole moiety and its use in thin-film organic field-effect transistors (OFETs) are reported. Compared to reported OFETs with other TTF derivatives, a high hole mobility up to 0.73 cm² V⁻¹ s⁻¹, low off-current and high on/off ratio up to 10⁵ are demonstrated. In addition, the developed OFETs show fast responsiveness toward chemical vapors of DECP (diethyl chlorophosphate) or POCl₃ which are simulants of phosphate-based nerve agents. In contrast to previously reported OFET-based sensors, off-current is used as the output signal, which increases quickly upon exposure to either DECP or POCl₃ vapors. High sensitivity is demonstrated toward DECP and POCl₃ vapors, with concentrations as low as 10 ppb being detected. These OFETs are also responsive to TNT vapor. The sensing mechanisms for the new type of OFET are discussed.

The simple one-pot syntheses of sulfur-rich thiepin-fused heteroacences with an alkylidene–fluorene framework, THA1 and THA6 (thiepin-fused heteroacene 1 or 6, in which the thiepin is conjugated at both ortho positions with SCH₃ or SC₆H₁₃, respectively), is reported. Based on electrochemical studies and theoretical calculations, their LUMO energies are relatively low (−3.26 eV), and their HOMO and HOMO−1 orbitals are nearly degenerate. The thiepin ring contributes mainly to HOMO−1 and LUMO orbitals, however, HOMO orbitals dominantly reside on thienoacence rings. Within the crystal of THA1, the molecules adopt a herringbone arrangement and multiple intermolecular interactions lead to the formation of a 2D network. Interestingly, THA6 shows totally different intermolecular arrangements. Organic field-effect transistor (OFET) devices show both compounds exhibiting p-type semiconducting behavior. Thin films or microcrystals of THA1 possess relatively high hole mobility. Moreover, the mobilities of the microcrystal of THA1 along three directions are in the same order, thus the hole-carrier transporting within the hexagonal-plane of microcrystal of THA1 exhibits less anisotropic behavior. In comparison, both thin films and microrods of THA6 show low hole mobilities. This agrees well with the intermolecular arrangements and interactions within crystal of THA6. Further theoretical calculations reveal that significant intermolecular electronic coupling among HOMO−1 orbitals and sulfur atoms play an important role in intermolecular electronic coupling for THA1.

Herein, we report the synthesis of new tetraphenylethylene derivatives 1, 2, 3, 4, 5 that feature electron-donating (methoxy) and -accepting (dicyanomethane) groups as AIE-active molecules with tunable emission colors. The crystal structures of compounds 3 and 4 are described and the intermolecular interactions within their crystals agree with the observation that they exhibit strong solid-state emission. Compounds 1, 2, 3, 4 exhibit typical AIE behavior and their emission maxima are red-shifted in the order: 1<2<3<4. Such red-shifts are ascribed to the fact that intramolecular interactions between the electron donor and the electron acceptor become stronger with increasing number of methoxy groups. The solid-state emission colors of compounds 1, 2, 3, 4 are successfully tuned from yellow-green to red. Compound 5 shows AIE behavior, but its emission is only slightly enhanced after aggregation and its solid shows a low quantum yield. Furthermore, microplates of compound 3 exhibit 2D optical-waveguide behavior.

The synthesis and optical investigations of di(p-methoxylphenyl)dibenzofulvene (1) and its analogues 2, 3, 4, 5, 6, and 7 with different lengths of alkoxyl chains are presented. All of these molecules exhibit emission in the solid state. The following interesting properties are reported for compound 1: 1) the solid-state fluorescence of 1 is dependent on the polymorphism forms; the two crystalline forms 1a and 1b are strongly blue- and yellow-green-emissive, whereas the amorphous solid is weakly fluorescent with orange emission; 2) on the basis of crystal-structural analysis, the intermolecular interactions will restrict the internal rotations, leading to fluorescence enhancement for the two crystalline forms 1a and 1b; however, the difference in emission color between 1a and 1b is ascribed to the molecular conformational alteration; 3) the solid-state fluorescence of 1 can be tuned by heating and cooling as well as grinding. Importantly, microrods of 1a and 1b exhibit outstanding optical waveguide behaviors. Moreover, amplified spontaneous emission for 1b and multimode-lasing behavior for 1a are presented. Besides the studies of compound 1, the crystal structures and solid-state fluorescence behaviors of 2, 3, 4, 5, 6, and 7 are also described.

Green fluorescent protein (GFP)-like chromophores 1–5, in which the p-hydroxylphenyl group is substituted with large aromatic moieties, were synthesized and their crystal structures were determined. Compared with that of p-hydroxybenzylideneimidazolinone (GFP chromophore), the fluorescence spectra of 1–5 are red-shifted because of elongated of π-conjugation. However, the incorporation of large aromatic moieties cannot inhibit the intramolecular torsional motions and, thus, 1–5 are generally weakly fluorescent in solution. The results manifest that the solid-state emission of these GFP-like chromophores is significantly influenced by the intermolecular packing. The emission spectra of 1–5 are further red-shifted in the solid-state, and 5 in the crystalline state emits in at red wavelengths with an emission maximum at 624 nm. 1, 3, and 4 are weakly emissive in both crystalline and powder forms. Interestingly, one crystalline state of 2 (2 B) emits relatively strongly, whereas another crystalline state 2 A emits rather weakly.

A triptycene-based cylindrical macrotricyclic molecule 1, which contains one tetrathiafulvalene (TTF) unit and four glycol chains, is reported. Both absorption and ESR spectroscopic studies clearly indicate that intermolecular electron transfer occurs from TTF in 1 to tetrachloroquinone in the presence of certain metal ions (e.g. Sc³⁺, Pb²⁺, and Zn²⁺). Based on comparative studies with 3 and 5, the close intermolecular alignment between 1 and tetrachloroquinone is proposed to occur by the synergic coordination of metal ions with oxygen atoms of the glycol chains and tetrachloroquinone (as well as the sulfur atoms of TTF). The intermolecular electron transfer is facilitated by the positive shift of the reduction potentials of tetrachloroquinone through coordination with metal ions, and the close alignment of 1 and tetrachloroquinone, which is beneficial for stabilizing the electron-transfer state.

A new electroactive polymer 1 with alternating NDI (naphthalene diimide) moieties and fluorinated alkyl chains was prepared and characterized. Gels of polymer 1 were formed in several solvents. Interestingly, gels of polymer 1 exhibited responsiveness toward N₂H₄, F⁻ and CN⁻. Absorption and ESR spectroscopic studies revealed that such responsiveness is owing to the reduction of NDI moieties into the respective NDI^.−. In addition, thin films of polymer 1 were easily prepared with spin-coating technique and the electrical conductivity of thin films reached 52.4 S/m after exposure to N₂H₄ vapor.

A new calix[4]arene 1 with tetrathiafulvalene (TTF), quinone, and crown ether units in the lower rim was designed and synthesized with the aim to investigate the possibility to tune the metal-ion promoted electron transfer by coordination of the crown ether unit with additional metal ions. Both absorption and electron spin resonance (ESR) spectroscopic studies clearly indicate that electron transfer occurs efficiently from TTF to the quinone units in the presence of Sc³⁺/Pb²⁺/Zn²⁺. Moreover, the intramolecular electron transfer within 1 induced by Zn²⁺ can be switched off by addition of Na⁺ and further turned on by addition of either Sc³⁺ or Pb²⁺.

The synthesis and characterization of four dendron-containing tetraphenylethylenes (TPEs), 1₁–1₄, were synthesized, along with a TPE compound that contained four OCH₂Ph groups (referred to as 1₀) for comparison. Photophysical studies revealed that the TPE core became emissive after linking dendrons onto its periphery. Moreover, the fluorescence intensity was significantly enhanced when high-generation dendrons were linked onto the TPE core; the fluorescence intensity increased in the following order: 1₁<1₂<1₃<1₄. This phenomenon was tentatively attributed to an enhancement in the energy barrier for internal rotation and torsion of the TPE core to which four dendrons were connected. In addition, the photocyclization of the TPE core into the respective 9,10-diphenylphenanthrene was facilitated when high-generation dendrons were linked to the TPE core. Again, the photocycliztion reactivity increased in the following order: 1₁<1₂<1₃<1₄. We found that the fluorescence and photocyclization reactivity of TPE could be modulated by covalent interactions with dendrons, and such modulation was strongly dependent on the dendron-generation.

The synthesis, self-assembly, and spectroscopic investigations of spiropyran (SP)-functionalized dendron 1 are reported. Under UV light irradiation, assembly of 1 into nano-/microparticles occurs due to the transformation of the closed form of SP into the open merocyanine (MC) form. The formation of these nano-/microparticles is confirmed by transmission electron microscopy (TEM) and dynamic light scattering (DLS) experiments in addition to the confocal laser scanning microscopy (CLSM) measurements. These nano-/microparticles exhibit relatively strong red emission. It is interesting to note that the direct cooling of the toluene/benzene solution of 1 to 0 °C leads to gel formation. Multivalent π–π interactions due to the dendron in 1 may be the driving-force for the gelation. The UV light irradiation cannot destroy the gel phase, and in fact, the gel–gel transition is successfully realized. The purple-blue gel exhibits relatively strong red fluorescence; moreover, the fluorescence can be reversibly switched by alternating UV and visible light irradiation. The results clearly indicate that the MC form after aggregation becomes more stable and fluorescent.

A dendron-substituted tetraphenylethene low molecular weight gelator (LMWG)compound, LMWG1, is designed and investigated. Gelation-induced fluorescence enhancement is observed for the gel based on LMWG1 and its fluorescence can be reversibly tuned by varying the temperature of the ensemble. The photoinduced energy-transfer can occur between LMWG1 and PI2 (perylene diimide) in the gel phase, but it cannot occur in the corresponding solution. The emission color of the gel of LMWG1 and PI2 can be tuned from cyan, yellow, to red by varying the concentration of PI2. By taking advantage of the photochromic transformation of spiropyran, the emission color of the organogels based on LMWG1 and SP3 can be switched by alternating UV and visible-light irradiations. The emission color can also be tuned by varying the irradiation time. In this way, organogels based on LMWG1 with multiemission color can be achieved in the presence of SP3 after light irradiations.

A new tetrathiafulvalene (TTF) derivative with two cholesterol units (compound 1) was synthesized and characterized. Gelation of n-hexane occurred after the hot solution of 1 was subjected to ultrasonic treatment for a few minutes. The resulting organogel was characterized with SEM, XRD and AFM. Besides heating the gel-sol transition also occurred upon addition of I₂ which can oxidize the TTF unit in 1. This result provides a new example of organogels responding to redox reactions. Interestingly, gelation-induced CD signals were observed and the CD signals can be tuned with the gel-sol transition which can be effected by heating and chemical reaction with I₂.

A 2,2′-bipyridyl-bridged tetrathiafulvalene (TTF)-quinone dyad (1) was synthesized and characterized. Both absorption and ESR spectroscopic studies clearly indicate that electron transfer occurs from TTF to the quinone unit for dyad 1 in the presence of metal ions. The results manifest that the coordination of dyad 1 with metal ions plays a key role in facilitating the intramolecular electron transfer.

By integrating the features of anthracene, 1,3-dithiole-2-thione, and binaphthalene units, (S)-1 and its analogue (S)-2, which contains two 1,3-dithiole-2-one units instead of 1,3-dithiole-2-thione, were studied for creating a new molecular regulation system and building a gated chiral molecular switch. The results show that the photodimerization is controlled by the remote functional-group transformation of CS into CO, thus providing an elegant example of molecular regulation. The photodimerization of two anthracene units induces circular dichroism (CD) spectral variation. Overall, the CD spectrum can be remotely modulated by Hg²⁺ in (S)-1, which leads to an Hg²⁺-gated chiral molecular switch.