Two L-phenylalanine derivatives with 5,8-bis(2-(carbazol-3-yl)vinyl)quinoxaline (PCQ) and 5,8-bis[2-(carbazol-3-yl)]-2,3-dimethylquinoxaline (DCQ) as fluorophores were synthesized, and their photophysical properties were measured and compared. The two compounds were found to gelate some organic solvents and self-assemble into 1D nanofibers in gels. The wet gel of PCQ emitted a weak orange fluorescence, but the DCQ gel had a strong green one. This result can be due to the presence of two methyl groups and the nonplanar conformation of fluorophore in DCQ. The gel film of DCQ also showed significantly stronger fluorescence than that of PCQ. Thus, the wet gel and xerogel film of DCQ were selected to study their sensing properties to acids. The yellow wet gel of DCQ transformed into a brown sol upon the addition of 0.2 equiv trifluoroacetic acid (TFA), accompanied by emission quenching. The xerogel film of DCQ rapidly responded to volatile acids, such as TFA, HCl, and HOAc. The fluorescence of the xerogel film was gradually quenched with increased concentration of volatile acid vapors. The fibrous film exhibited low detection limits for volatile acid. The detection limits of the thin films for TFA, HCl, and HOAc reached 43, 122, and 950 ppb, respectively.

Nanofibers based on phenanthroimidazole derivatives PCC, PDC, and PSC were fabricated by organogelation processes, and their fluorescence sensory properties towards acid were investigated. It was found that the emission of PCC in the nanofiber-based film could be quenched significantly upon exposure to gaseous TFA due to the formation of protonated PCC, in which ICT (intramolecular charge transfer) would occur. On the other hand, TFA vapor led to the emitting colors of PDC and PSC in the nanofiber-based films to turn to yellow and green from sky blue and blue, respectively. Additionally, we found that the decay times of PCC were 0.1 s and 1.9 s in probing the saturated vapor of TFA in nanofiber-based film and in spin-coated film, respectively. The results suggested that the high surface-to-volume ratio and large interspace in the nanofiber-based networks favored the enhanced adsorption, accumulation, and diffusion of gaseous molecules, resulting in such a high performance.

Fluorescent organic molecules with C₃-symmetry consisting of tris{2-cyano-2-[4-(dodecyloxybenzoylamino)phenyl]-1-ethenyl}phenylbenzene (CN-DBAPPBn, n = 1, 2, 3) were synthesized. It was observed that these compounds can spontaneously self-assemble into organogels in many organic solvents. Scanning electron microscopy (SEM), light microscopy, and fluorescence microscopy images of the air-dried gels showed the presence of either heavily entangled amorphous or fibrous structures, or rods. FTIR, UV/Vis absorption, excitation and emission spectra suggest that π–π interactions and H-bonding are the driving forces for the formation of the gel phases. Moreover, spherical or cubic fluorescent nanoparticles based on CN-DBAPPBn were prepared by using a reprecipitation method in a mixture of tetrahydrofuran and water. It is interesting that aggregation-induced emission behavior of CN-DBAPPBn was detected in both the gel phase and in the nanoparticle suspensions. The fluorescent molecular aggregates of CN-DBAPPBn with different architectures and emission properties fabricated by using these self-assembling methods could find potential applications in sensors and optoelectronic devices.

The simplest carbazole-based organogelator C1 (9-hexadecyl-9H-carbazole) has been synthesized and can self-assemble into nanofibers in the gel phase directed by balanced π–π interactions. To extend the conjugation of the π gelator, we prepared linear carbazole-based trimer C3 and pentamer C5, which also exhibited gelation behavior in some organic solvents upon ultrasound stimulation. It is found that the xerogel of C3 emits strong blue light under UV irradiation. Notably, the emission of C3 in nanofiber-based films can be quenched upon exposure to vapors of TNT and DNT. The steady-state Stern–Volmer plots of C3 in toluene revealed that the fluorescent quenching induced by aromatic nitro compounds is due to photoinduced electron transfer. Therefore the emitting nanofibers fabricated from linear carbazole by organogelation can be used as fluorescent sensors to detect explosives.

A series of new triphenylamine-functionalized bis(β-diketone)s bridged by a carbazole (CnBDKC, n=1, 4, 8, 16) with twisted intramolecular charge-transfer emission in polar solvents has been synthesized. The length of the carbon chains has a significant effect on the self-assembling properties of the compounds. Well-defined 1D nanowires were easily generated from C1BDKC with a methyl group by a reprecipitation approach directed by π-stacking interaction, and the molecules packed into J-aggregates in the nanowires. In addition, 1D nanofibers based on C16BDKC bearing a long hexadecyl chain were prepared through the organogelation process, and H-aggregates were formed driven by the synergistic effect of π-stacking interaction and van der Waals force in the gel phase. C4BDKC and C8BDKC containing butyl and octyl side chains, respectively, cannot arrange into dispersed nanostructures, probably because π–π interaction between conjugated moieties might be disturbed by the interaction between the side chains, which is, however, not strong enough to dominate the self-assembling process. Notably, the nanowires based on C1BDKC and the gel nanofibers from C16BDKC can emit strong green light under irradiation, which suggests that these 1D nanomaterials may have potential applications in emitting materials as well as photonic devices.

Novel star-shaped subporphyrins with monodisperse oligocarbazole arms were prepared by using pyridine-tri-N-pyrrolylborane as a template. It was found that photoinduced energy transfer took place from the oligocarbazole arms to the subporphyrin core, and the energy transfer efficiency decreased with an increase in the number of carbazole units in the arms. These subporphyrins could emit intense yellow-green light when they were excited at 295 nm. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

A series of novel dendritic carbazole-functionalized subporphyrins, T(Cz-Gn)SubPs (n = 1–3), have been synthesized from pyridine–tri(pyrrol-1-yl)borane and the corresponding aldehydes. This study has demonstrated that intramolecular energy transfer from the carbazole dendron to the subporphyrin core occurs with a high efficiency which decreases with increasing dendron generation, in accord with the Förster mechanism of energy transfer. In addition, the carbazole dendron can lead to a blueshift of the absorption and emission bands of the subporphyrin core. The light-harvesting abilities of these compounds increase with increasing generation. Meanwhile, these dendritic macromolecules emit intense yellow-green light and may be good candidates for photonic devices. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)