Panchromatic and Perturbed Absorption Spectral Features and Multiredox Properties of Dicyanovinyl- and Dicyanobutadienyl-Appended Cobalt Corroles

Four new β-functionalized π-extended cobalt corroles with one and two dicyanovinyl (DCV) or dicyanobutadienyl (DCBD) moieties at the 3- and 3,17-positions have been synthesized and characterized by various spectroscopic techniques. Interestingly, the synthesized DCV- and DCBD-appended cobalt corroles displayed panchromatic and near-infrared absorption in the range 300-1100 nm in CH2Cl2 and pyridine solvents. (MN)2-(Cor)Co and A2MN2-(Cor)Co exhibited 8-9 times enhancement in the molar absorptivity of the Q band compared to the parent corrole ((Cor)Co). The unique absorption spectral features of these β-functionalized cobalt corroles are splitting, broadening, and red-shifting in the Soret and Q bands. One DCV unit brings a 30-46 nm red shift, whereas one DCBD unit brings a 40-75 nm red shift in the Q band compared to the corresponding precursors. This is rare that the intensity of the longest Q band is greater than or equal to the Soret-like bands. These corrole derivatives exhibit UV-vis spectral features similar to those of chlorophyll a. A 220 mV positive shift per DCV group and 160 mV positive shift per DCBD group were observed in the first oxidation potentials compared to (Cor)Co in the desired direction for the utility of these cobalt complexes in electrocatalysis. DFT studies revealed that HOMO and LUMO were stabilized after appending DCV and DCBD groups on the corrole macrocycle and exhibited a "push-pull" behavior leading to promising material applications in nonlinear optics (NLO) and catalysis.

Quantum dynamics of the photoinduced charge separation in a symmetric donor–acceptor–donor triad: The role of vibronic couplings, symmetry and temperature

The photoinduced charge separation in a symmetric donor–acceptor–donor (D–A–D) triad is studied quantum mechanically using a realistic diabatic vibronic coupling model. The model includes a locally excited DA*D state and two charge-transfer states D+A−D and DA−D+ and is constructed according to a procedure generally applicable to semirigid D–A–D structures and based on energies, forces, and force constants obtained by quantum chemical calculations. In this case, the electronic structure is described by time-dependent density functional theory, and the corrected linear response is used in conjunction with the polarizable continuum model to account for state-specific solvent effects. The multimode dynamics following the photoexcitation to the locally excited state are simulated by the hybrid Gaussian-multiconfigurational time-dependent Hartree method, and temperature effects are included using thermo field theory. The dynamics are connected to the transient absorption spectrum obtained in recent experiments, which is simulated and fully assigned from first principles. It is found that the charge separation is mediated by symmetry-breaking vibrations of relatively low frequency, which implies that temperature should be accounted for to obtain reliable estimates of the charge transfer rate.

Magnesium Phthalocyanines and Tetrapyrazinoporphyrazines: The Influence of a Solvent and a Delivery System on a Dissociation of Central Metal in Acidic Media

Magnesium complexes of phthalocyanines (Pcs) and their aza-analogues have a great potential in medical applications or fluorescence detection. They are known to demetallate to metal-free ligands in acidic environments, however, detailed investigation of this process and its possible prevention is lacking. In this work, a conversion of lipophilic and water-soluble magnesium complexes of Pcs and tetrapyrazinoporphyrazines (TPyzPzs) to metal-free ligands was studied in relation to the acidity of the environment (organic solvent, water) including the investigation of the role of delivery systems (microemulsion or liposomes) in improvement in their acido-stability. The mechanism of the demetallation in organic solvents was based on an acidoprotolytic mechanism with the protonation of the azomethine nitrogen as the first step and a subsequent conversion to non-protonated metal-free ligands. In water, the mechanism seemed to be solvoprotolytic without any protonated intermediate. The water-soluble magnesium complexes were stable in a buffer with a physiological pH 7.4 while a time-dependent demetallation was observed in acidic pH. The demetallation was immediate at pH < 2 while the full conversion to metal-free ligand was done within 10 min and 45 min for TPyzPzs at pH 3 and pH 4, respectively. Incorporation of lipophilic magnesium complexes into microemulsion or liposomes substantially decreased the rate of the demetallation with the latter delivery system being much more efficient in the protection from the acidic environment. A comparison of two different macrocyclic cores revealed significantly higher kinetic inertness of magnesium TPyzPz complexes than their Pc analogues.

Novel DBMBF2-BODIPY dyads connected via a flexible linker: synthesis and photophysical properties

Novel BODIPY and DBMBF2 dyads connected via a flexible trisiloxane linker were synthesized and their photophysical properties were investigated.

Efficient Synthesis of a Wide-Range Absorbing Azaphthalocyanine Dark Quencher and Its Application to Dual-Labeled Oligonucleotide Probes for Quantitative Real-Time Polymerase Chain Reactions

Unsymmetrical dialkylamino-substituted zinc azaphthalocyanine (AzaPc) exhibits unique spectral and photophysical properties for dark quenchers of fluorescence in DNA hybridization probes. The panchromatic light absorption of AzaPc from 300 nm up to at least 700 nm and its lack of fluorescence make it an ideal candidate for a universal dark quencher. To prove this experimentally, oligodeoxyribonucleotide probes were labeled at the 3'-end by this AzaPc and at the 5'-end by a fluorophore used in the polymerase chain reaction (PCR)-that is, fluorescein, CAL Fluor Red 610, and Cy5. AzaPc showed a significantly higher quenching efficiency compared to the commercially available dark quenchers (BHQ-1, BHQ-2, BBQ-650) in a developed model of TaqMan PCR assay. The AzaPc-labeled probe proved to also be useful in a practical PCR assay for the quantification of the SLCO2B1 transporter gene expression. The constructed calibration curves indicated linearity in the range from 10² to 10⁷ of target copies.

Azophenine as Central Core for Efficient Light Harvesting Devices

The notoriously non-luminescent uncycled azophenine (Q) was harnessed with Bodipy and zinc(II)porphyrin antennas to probe its fluorescence properties, its ability to act as a singlet excited state energy acceptor and to mediate the transfer. Two near-IR emissions are depicted from time-resolved fluorescence spectroscopy, which are most likely due to the presence of tautomers of very similar calculated total energies (350 cm^-1 ; DFT; B3LYP). The rates for energy transfer, k_ET (S₁ ), for ¹ Bodipy*→Q are in the order of 10¹⁰ -10¹¹  s^-1 and are surprisingly fast when considering the low absorptivity properties of the lowest energy charge transfer excited state of azophenine. The rational is provided by the calculated frontier molecular orbitals (MOs) which show atomic contributions in the C₆ H₄ C≡CC₆ H₄ arms, thus favoring the double electron exchange mechanism. In the mixed-antenna Bodipy-porphyrin star molecule, the rate for ¹ Bodipy*→porphyrin has also been evaluated (≈16×10¹⁰  s^-1 ) and is among the fastest rates reported for Bodipy-zinc(II)porphyrin pairs. This astonishing result is again explained from the atomic contributions of the C₆ H₄ C≡CC₆ H₄ and C≡CC₆ H₄ arms thus favouring the Dexter process. Here, for the first time, this process is found to be sensitively temperature-dependent. The azophenine turns out to be excellent for electronic communication.

Rational molecular design enhancing the photonic performance of red-emitting perylene bisimide dyes

We report the synthesis of novel multichromophoric organic architectures, where perylene red is decorated with BODIPY and/or hydroxycoumarin dyes acting as light harvesters and energy donors. The computationally-aided photophysical study of these molecular assemblies reveals a broadband absorption which, regardless of the excitation wavelength, leads solely to a bright red-edge emission from perylene bisimide after efficient intramolecular energy transfer hops. The increase of the absorbance of these molecular antennas at key pumping wavelengths enhances the laser action of the commercial perylene red. The herein applied strategy based on energy transfer dye lasers should boost the use of perylene-based dyes as active media for red-emitting lasers.

Modelling excitation energy transfer in covalently linked molecular dyads containing a BODIPY unit and a macrocycle

We model the singlet–singlet Excitation Energy Transfer (EET) process in a panel of large BODIPY–macrocycle dyads, including some azacalixphyrin derivatives.

n- versus p-doping of graphite: what drives its wet-chemical exfoliation?

We have performed the syntheses of a novel pyrene-porphyrazine conjugate (ZnPzPy) and a reference porphyrazine (ZnPz) to promote the wet-chemical exfoliation of graphite based on the synergetic use of ultrasonication, centrifugation, and doping. ZnPzPy features, on one hand, a hydrophobic pyrene to anchor onto the basal plane of graphene, and, on the other hand, an amphoteric porphyrazine to either p- or n-dope graphene. To this end, we have characterized individual building blocks, that is, ZnPzPy and exfoliated graphite, and the resulting electron donor-acceptor nanohybrid, that is, ZnPzPy/graphene (ZnPzPy-G), by means of an arsenal of microscopic and spectroscopic techniques. From a full-fledged characterization we conclude that ZnPzPy facilitates the exfoliation of graphite affording suspensions featuring 9.5% of single- or few-layered ZnPzPy-G with a mean average size of 200 ± 140 nm. Importantly, a notable shift of charge density from graphene to ZnPzPy in the ground state of ZnPzPy-G corroborates the preference of exfoliated graphite to undergo p-doping rather than n-doping. As an immediate consequence, a full charge separation leads in the excited state to a 750 ± 150 ps lived charge separated state.

OFF-ON-OFF Red-Emitting Fluorescent Indicators for a Narrow pH Window

A unique combination of two independent mechanisms of fluorescence quenching, namely intramolecular charge transfer (ICT) from a peripheral donor and protonation of azomethine nitrogen atoms in zinc tetrapyrazinoporphyrazines (TPyzPz), provides a new possibility for sensing pH in a specific range. The pH selectivity was controlled by the different basicities of the donor for ICT (dimethylaminoaryl), which was connected to the macrocycle by π-extended linkers of different lengths. ICT and protonation have been studied in detail by photophysical, spectral (UV/Vis and MCD spectra), and electrochemical measurements, and further supported by theoretical calculations (DFT, TDDFT). The pH-sensing properties of the TPyzPzs have been investigated in THF and in water after anchoring the TPyzPzs to liposomes. The salient pK_a values were around 1.3 (azomethine nitrogen) and 2.29-4.76 (donor for ICT). The lead indicators (sensing over a pH range of 1.0-2.5) with fairly steep sensing profiles exhibited increases in fluorescence between the OFF/ON states of more than 20-fold and strong absorption in the red region (Q-band maximum >650 nm, ϵ≈2×10⁶  m^-1  cm^-1 ).

Synthesis and properties of novel star-shaped oligofluorene conjugated systems with BODIPY cores

Star-shaped conjugated systems with varying oligofluorene arm length and substitution patterns of the central BODIPY core have been synthesised, leading to two families of compounds, T-B1–T-B4 and Y-B1–Y-B4, with T- and Y-shaped motifs, respectively. Thermal stability, cyclic voltammetry, absorption and photoluminescence spectroscopy of each member of these two families were studied in order to determine their suitability as emissive materials in photonic applications.

An asymmetric BODIPY triad with panchromatic absorption for high-performance red-edge laser emission

From a judicious synthetic design based on BODIPY scaffolds UV-vis panchromatic absorption with valuable red laser emission is achieved.