A key intermediate compound, 2,5,8,11-tetrabromo-1,6,7,12-tetrabutoxyperylene (Per-4Br), was synthesized from 3,6-dibromo-2,7-dioxylnaphthalene via simple regioselective oxidative radical–radical coupling, followed by reduction and nucleophilic substitution. Various bay- and ortho-octasubstituted perylenes containing cyano, methoxy and aryl groups were then obtained by nucleophilic substitution or Pd-catalyzed coupling reactions. X-ray crystallographic analyses reveal that these new perylene molecules process a twisted structure due to steric congestion at the bay-regions and there is no obvious intermolecular π–π interaction. As a result, they exhibit moderate fluorescence quantum yields even in solid state. Therefore, Per-4Br can serve as a versatile building block for various functional perylene dyes with tunable optoelectronic property.

Despite the great potential of heteroatom-containing polycyclic aromatic hydrocarbons in organic optoelectronics, there are very limited reports on heteroaromatics containing a B–N–B bond in the π-scaffold. Herein, stable 1,9-dibora-9a-azaphenalenyl (DBAP) derivatives, named BNB-embedded phenalenyls, are presented. The DBAP skeleton contains a three-center two-π-electron B–N–B moiety with 12 π-electrons and can be regarded as the isoelectronic structure of the phenalenyl cation. Chemical reduction of the phenyl derivative of DBAP by potassium generated the dianion containing 14 delocalized π-electrons, which can be regarded as the isoelectronic structure of the phenalenyl anion. The dianion is sandwiched and stabilized by two bulky [K([18]crown-6)]+ counterions according to its X-ray structure. However, its monoanion (an isoelectronic structure of the henalenyl radical) generated by mixing equal moles of neutral compound and dianion gave an unusual B–N–B-embedded benzo[cd]fluoranthene dianion, which again was confirmed by X-ray crystallographic analysis. The new dianion containing 20 π-electrons is highly aromatic and is further stabilized by [K([18]crown-6)]+ counterions. An aromaticity driven rearrangement mechanism was proposed for this unusual transformation. Based on X-ray structures and theoretical calculations, the B–N–B moiety in the neutral and anionic DBAP participates in the π-electron delocalization along the whole DBAP skeleton like their phenalenyl cation/radical/anion counterparts, but with more localized character. Therefore, our studies report the first synthesis and characterization of a B–N–B-embedded phenalenyl and its anionic species, which show unique electronic structure and unusual reactivity different from that of their all-carbon phenalenyl analogues.

A new class of pyridazine fused aromatics, 1,2-diazabenzo[ghi]perylenes, is conveniently synthesized from 2,7-dihydroxynaphthalene via intermolecular oxidative coupling followed by a condensation reaction. These new compounds are fully characterized via X-ray crystallographic analysis, optical spectroscopy and electrochemistry, in addition to DFT calculations. They show a twisted structure and unique P-/P- and M-/M-enantiomer pairs are observed in their single crystals. They exhibit intramolecular charge transfer character and emit at a longer wavelength with a larger Stokes shift compared with their all-carbon analog.

D 3h symmetric hexa-peri-hexabenzocoronene substituted by three carboxylic acid groups (HBC-COOH) was synthesized. HBC-COOH formed a rigid two-dimensional (2D) honeycomb network at a solid–liquid interface via intermolecular hydrogen bonding interactions. Guest molecules such as coronene can fill the cavities of this porous 2D network.

•A dihydroxy perylenequinonoid dye (DHPQ) is exploited as an effective probe for hydrogen persulfide detection.•DHPQ is found to be reversible fluorescent probe due to the excited state intramolecular hydrogen transfer process.•DHPQ exhibits a highly sensitive turn-on fluorescence (600-fold enhanced response) and low detection limit (18.2 nM).•The reversible detection method has been successfully used in both solvents and living HeLa cells.Hydrogen persulfide (H2S2), as a direct redox form of H2S, may have its own physiological processes in maintaining intracellular redox homeostasis. The research on hydrogen persulfide was rapidly growing. As it is the actual signalling molecules derived from hydrogen sulfide, reversible detection of hydrogen persulfide changes in cells is of great significance. To address this critical need, we present a reversible fluorescent switch-on H2S2 probe, the tautomeric of 6, 7-dihydroxyperylene-1, 12-quinone (DHPQ), capable of tracking H2S2 in solvents and living cells. The probe can be applied to quantified H2S2 expressions ranging linearly from 2.0×10−62.0×10−6 to 2.0×10−52.0×10−5 M. The limit of detection was found to be 1.82×10−81.82×10−8 M. In addition, the fluorescent alterations are remarkably specific for H2S2 in the presence of other reactive sulfur species. These features are favorable for imaging application. Taking advantage of favorable cycle stability and admirable selectivity, the DHPQ dye can be used as a reversible fluorescent platform to construct novel H2S2 probes. Since such reversible H2S2 probes are rare, this work provide a potential approach for reversible probing fluctuation of hydrogen persulfide in biological systems.

9-Ethynylfluorenyl radical derivatives were readily prepared in situ and underwent simultaneous intermolecular coupling reactions. Interestingly, the dimerization process took place in either a head-to-tail or a head-to-head mode between the acetylenic or the allenic resonance forms dependent on the terminal substituents, which could be well explained by their different spin distribution and steric hindrance effects. The structures of the products were confirmed by X-ray crystallographic and other spectroscopic analyses. It was also found that the newly generated dipropinyl dimers underwent a rearrangement and ring-cyclization reaction at room temperature, eventually giving unique difluorenylidene cyclobutene derivatives.

Fast sulfonylation of pyridine/quinoline N-oxides induced by iodine is demonstrated herein. The regioselective protocol occurs under metal-free conditions in a short reaction time (10 min), exhibiting high efficiency (up to 92% yield) and good compatibility (up to 33 examples). A gram-scale reaction was conducted with only a slight loss of production.

Two-photon excitation (TPE) probe-based fluorescence imaging has become one of the most attractive diagnostic techniques to investigate biomolecules and biological events in live cells and tissues. At the current stage most of the TPE-based sensing is reflected by fluorescence intensity changes. Nevertheless the mere altering of intensity could be facilely affected by ambient conditions. On the other hand, TPE probes based on an intramolecular charge transfer (ICT) strategy could solve this problem to some extent with a morphology change-induced emission shift. However their applications are yet constrained due to the inherent limitation of ICT, e.g. the high degree of overlap of two emissions bands and shifts of the TPE maxima. To achieve the desired TPE-based sensing and to circumvent the problems stated above, we adapted a Förster resonance energy transfer (FRET) strategy to develop small molecule ratiometric TPE fluorescent probes. Our FRET-based ratiometric TPE fluorescent probe displays a remarkable emission shift (up to 125 nm) with two well-resolved emission bands. Hence the ratio of these two emission bands could enable the measurement of fluorescence changes more accurately, thus further improving imaging in live cells and deep tissues. To the best of our knowledge, the current reported probe has the largest emission shift among all the small molecule ratiometric TPE fluorescent probes while the maximum TPE wavelength remains unchanged. This work has provided a FRET approach to fabricate novel small molecule ratiometric TPE fluorescent probes that improve imaging in deep tissues.

A new class of pyridazine fused aromatics, 1,2-diazabenzo[ghi]perylenes, is conveniently synthesized from 2,7-dihydroxynaphthalene via intermolecular oxidative coupling followed by a condensation reaction. These new compounds are fully characterized via X-ray crystallographic analysis, optical spectroscopy and electrochemistry, in addition to DFT calculations. They show a twisted structure and unique P-/P- and M-/M-enantiomer pairs are observed in their single crystals. They exhibit intramolecular charge transfer character and emit at a longer wavelength with a larger Stokes shift compared with their all-carbon analog.

Two-photon excitation (TPE) probe-based fluorescence imaging has become one of the most attractive diagnostic techniques to investigate biomolecules and biological events in live cells and tissues. At the current stage most of the TPE-based sensing is reflected by fluorescence intensity changes. Nevertheless the mere altering of intensity could be facilely affected by ambient conditions. On the other hand, TPE probes based on an intramolecular charge transfer (ICT) strategy could solve this problem to some extent with a morphology change-induced emission shift. However their applications are yet constrained due to the inherent limitation of ICT, e.g. the high degree of overlap of two emissions bands and shifts of the TPE maxima. To achieve the desired TPE-based sensing and to circumvent the problems stated above, we adapted a Förster resonance energy transfer (FRET) strategy to develop small molecule ratiometric TPE fluorescent probes. Our FRET-based ratiometric TPE fluorescent probe displays a remarkable emission shift (up to 125 nm) with two well-resolved emission bands. Hence the ratio of these two emission bands could enable the measurement of fluorescence changes more accurately, thus further improving imaging in live cells and deep tissues. To the best of our knowledge, the current reported probe has the largest emission shift among all the small molecule ratiometric TPE fluorescent probes while the maximum TPE wavelength remains unchanged. This work has provided a FRET approach to fabricate novel small molecule ratiometric TPE fluorescent probes that improve imaging in deep tissues.

Fast sulfonylation of pyridine/quinoline N-oxides induced by iodine is demonstrated herein. The regioselective protocol occurs under metal-free conditions in a short reaction time (10 min), exhibiting high efficiency (up to 92% yield) and good compatibility (up to 33 examples). A gram-scale reaction was conducted with only a slight loss of production.