Electronic, Spectroscopic, and Ion-Sensing Properties of a Dehydro[<i>m</i>]pyrido[14]- and [15]annulene Isomer Library

An isomeric series of dehydro­[<i>m</i>]­pyrido­[<i>n</i>]­annulenes incorporating strained 1,4-buta-1,3-diyne units have been synthesized, where <i>m</i> = 2, <i>n</i> = 14 (<b>1a</b>–<b>d</b>); <i>m</i> = 2, <i>n</i> = 15 (<b>2a</b>,<b>b</b>); and <i>m</i> = 3, <i>n</i> = 15 (<b>3</b>). The number of pyridine rings and annulene ring π-electrons are denoted by <i>m</i> and <i>n</i>, respectively. The X-ray crystal structures of <b>1b</b> and <b>1c</b> confirmed their cyclic formulation. All macrocycles were found to be luminescent chromophores with differing isomer-dependent proton and metal ion-sensory emission responses, which appear collectively as analyte-specific color patterns. Within the series studied, <b>1a</b> was singular in displaying the highest luminescence quantum yield and sharing the strongest emission energy and molar absorption changes upon protonation and Hg^II binding. Spectroscopic and electrochemical results were supported by density functional theory calculations in showing <b>1a</b>, <b>2a</b>, and <b>3</b> to be low bandgap materials with lowest unoccupied molecular orbitals delocalized over the 1,4-di­(pyridin-4-yl)­buta-1,3-diyne bridges that provide a pathway for electronic communication between the nitrogens. Overall, the investigations suggest that <b>1a</b>, <b>2a</b>, and <b>3</b> would be excellent ligands for the construction of novel conjugated hybrid metallosupramolecular nanostructures, polymers, and ion-sensory systems

Synthesis and Properties of Arylvinylidene-Bridged Triphenylamines

A series of arylvinylidene-bridged triphenylamines were efficiently synthesized through the thionation/Barton–Kellogg olefination sequence from their corresponding carbonyl precursors. The electrochemical investigations identified these highly distorted scaffolds as fairly strong electron donors capable of several reversible oxidation steps with the first oxidation occurring at a potential comparable to that of ferrocene for the <i>n</i>-hexyl-substituted diphenylvinylidene-bridged compound

Electronic, Spectroscopic, and Ion-Sensing Properties of a Dehydro[<i>m</i>]pyrido[14]- and [15]annulene Isomer Library

An isomeric series of dehydro­[<i>m</i>]­pyrido­[<i>n</i>]­annulenes incorporating strained 1,4-buta-1,3-diyne units have been synthesized, where <i>m</i> = 2, <i>n</i> = 14 (<b>1a</b>–<b>d</b>); <i>m</i> = 2, <i>n</i> = 15 (<b>2a</b>,<b>b</b>); and <i>m</i> = 3, <i>n</i> = 15 (<b>3</b>). The number of pyridine rings and annulene ring π-electrons are denoted by <i>m</i> and <i>n</i>, respectively. The X-ray crystal structures of <b>1b</b> and <b>1c</b> confirmed their cyclic formulation. All macrocycles were found to be luminescent chromophores with differing isomer-dependent proton and metal ion-sensory emission responses, which appear collectively as analyte-specific color patterns. Within the series studied, <b>1a</b> was singular in displaying the highest luminescence quantum yield and sharing the strongest emission energy and molar absorption changes upon protonation and Hg^II binding. Spectroscopic and electrochemical results were supported by density functional theory calculations in showing <b>1a</b>, <b>2a</b>, and <b>3</b> to be low bandgap materials with lowest unoccupied molecular orbitals delocalized over the 1,4-di­(pyridin-4-yl)­buta-1,3-diyne bridges that provide a pathway for electronic communication between the nitrogens. Overall, the investigations suggest that <b>1a</b>, <b>2a</b>, and <b>3</b> would be excellent ligands for the construction of novel conjugated hybrid metallosupramolecular nanostructures, polymers, and ion-sensory systems

Electronic, Spectroscopic, and Ion-Sensing Properties of a Dehydro[<i>m</i>]pyrido[14]- and [15]annulene Isomer Library

An isomeric series of dehydro­[<i>m</i>]­pyrido­[<i>n</i>]­annulenes incorporating strained 1,4-buta-1,3-diyne units have been synthesized, where <i>m</i> = 2, <i>n</i> = 14 (<b>1a</b>–<b>d</b>); <i>m</i> = 2, <i>n</i> = 15 (<b>2a</b>,<b>b</b>); and <i>m</i> = 3, <i>n</i> = 15 (<b>3</b>). The number of pyridine rings and annulene ring π-electrons are denoted by <i>m</i> and <i>n</i>, respectively. The X-ray crystal structures of <b>1b</b> and <b>1c</b> confirmed their cyclic formulation. All macrocycles were found to be luminescent chromophores with differing isomer-dependent proton and metal ion-sensory emission responses, which appear collectively as analyte-specific color patterns. Within the series studied, <b>1a</b> was singular in displaying the highest luminescence quantum yield and sharing the strongest emission energy and molar absorption changes upon protonation and Hg^II binding. Spectroscopic and electrochemical results were supported by density functional theory calculations in showing <b>1a</b>, <b>2a</b>, and <b>3</b> to be low bandgap materials with lowest unoccupied molecular orbitals delocalized over the 1,4-di­(pyridin-4-yl)­buta-1,3-diyne bridges that provide a pathway for electronic communication between the nitrogens. Overall, the investigations suggest that <b>1a</b>, <b>2a</b>, and <b>3</b> would be excellent ligands for the construction of novel conjugated hybrid metallosupramolecular nanostructures, polymers, and ion-sensory systems

Synthesis and Electrochemical Studies of Porphyrin Dimers Linked by Metallocarbenes

The functionalization of porphyrins at the <i>meso</i> positions by azoles led, after subsequent alkylation, to several precursors of N-heterocyclic carbenes. Porphyrin dimers linked by palladium (or rhodium) bis-carbene spacers were prepared and characterized. Spectroscopic data and X-ray structures showed that the coordination geometry for the two carbenes around the palladium linker was <i>trans-anti</i>. Electrochemical studies revealed significant electronic communication between the two porphyrins, despite the absence of conjugation pathways

Synthesis and Electrochemical Studies of Porphyrin Dimers Linked by Metallocarbenes

The functionalization of porphyrins at the <i>meso</i> positions by azoles led, after subsequent alkylation, to several precursors of N-heterocyclic carbenes. Porphyrin dimers linked by palladium (or rhodium) bis-carbene spacers were prepared and characterized. Spectroscopic data and X-ray structures showed that the coordination geometry for the two carbenes around the palladium linker was <i>trans-anti</i>. Electrochemical studies revealed significant electronic communication between the two porphyrins, despite the absence of conjugation pathways

One-Pot Access to Push–Pull Oligoenes by Sequential [2 + 2] Cycloaddition–Retroelectrocyclization Reactions

The formal [2 + 2] cycloaddition–retroelectrocyclization reaction was employed as the key transformation to obtain donor-substituted, π-conjugated polycyanohexa-1,3,5-trienes (TCHTs and PCHTs) and polycyanoocta-1,3,5,7-tetraenes from donor-substituted tetracyanobuta-1,3-dienes (TCBDs) and electron-rich alkynes. These push–pull-substituted oligoene chromophores were also accessed in good yield from tetracyanoethylene and donor-substituted alkynes by using a one-pot protocol. All bis-(<i>N</i>,<i>N</i>-dialkylanilino) donor-substituted push–pull trienes and tetraenes showed better electron-accepting potency and lower HOMO–LUMO gaps than the corresponding TCBDs, as evidenced by optical and electrochemical studies

Redox-Switchable Resorcin[4]arene Cavitands: Molecular Grippers

Diquinone-based resorcin[4]­arene cavitands that open to a kite and close to a vase form upon changing their redox state, thereby releasing and binding guests, have been prepared and studied. The switching mechanism is based on intramolecular H-bonding interactions that stabilize the vase form and are only present in the reduced hydroquinone state. The intramolecular H-bonds were characterized using X-ray, IR, and NMR spectroscopies. Guests were bound in the closed, reduced state and fully released in the open, oxidized state

Synthesis and Optoelectronic Properties of <i>Janus</i>-Dendrimer-Type Multivalent Donor–Acceptor Systems

A convergent, multistep protocol was employed for the synthesis of a <i>Janus</i>-type multivalent donor–acceptor system. The synthetic approach is based on a Sonogashira cross-coupling of two differently ferrocene-(Fc) substituted dendrons and a final sixfold [2 + 2] cycloaddition−retroelectrocyclization (CA−RE) reaction with tetracyanoethene, which occurs regioselectively at only one of the rigidly linked dendrons. The structural and optoelectronic properties of the compounds were investigated by X-ray analysis, UV/vis spectroscopy, and electrochemistry. The target <i>Janus</i>-system displays redox-amphoteric behavior. The nonalkynylated Fc end groups in one dendron are readily and reversibly oxidized. The second dendron, in which the terminal Fc-activated alkynes underwent the CA−RE reaction to give tetracyanobuta-1,3-dienes in the final step of the synthesis, undergoes four reversible 3-e^– reductions in the very narrow potential range of 1 V. A spontaneous intramolecular charge transfer from the donor into the acceptor hemisphere was not observed. Furthermore, the oxidation potential of the Fc donors in one hemisphere is hardly perturbed by the push–pull acceptors in the other, which suggests that electronic communication along the π-system, with several <i>meta</i>-connectivities, is not efficient. Therefore, the charge-transfer bands seen in the <i>Janus</i>-type system originate from the interaction of the Fc donors with the directly connected tetracyanobuta-1,3-diene acceptors in the same hemisphere

Cascade Carbopalladation Reaction between Alkynes and <i>gem</i>-Dibromoolefins: Facile Access to Monoannelated Pentalenes

A carbopalladation cascade reaction of easily accessible <i>gem</i>-dibromoolefins and alkynes furnishes monobenzo- and mononaphthopentalenes. The new chromophores accessed by this short route exhibit small HOMO–LUMO gaps and redox amphoteric behavior with tunable redox potentials