Recent advances in subphthalocyanines and related subporphyrinoids

Subporphyrinoids constitute a class of extremely versatile and attractive compounds. Herein, a comprehensive review of the most recent advances in the fundamentals and applications of these cone-shaped aromatic macrocycles is presented.

Modulating the dynamics of Förster resonance energy transfer and singlet fission by variable molecular spacers

In contrast to previous work, the synergy between panchromatic absorption and molecular singlet fission (SF) is exploited to optimize solar energy conversion through evaluation of the distance dependence of intramolecular Förster Resonance Energy Transfer (i-FRET) in a series of subphthalocyanines (SubPcs) linked to pentacene dimers (Pnc2s). To provide control over i-FRET, the molecular spacer rather than the energy donating SubPc is tailored in the corresponding SubPc-Pnc2 conjugates in terms of length (i.e., the number of aryl units) and flexibility (i.e., presence or absence of a CH2 group). AM1-CIS calculations support the experiments, which underline the importance of the molecular spacer to impact not only the i-FRET dynamics, but also the dynamics of intramolecular singlet fission (i-SF). For example, an additional phenyl group slows down both i-FRET and i-SF by a factor of ∼3.8 and ∼1.6, respectively, by a quinone-like conjugation pattern that affords a pentacene acceptor orbital that is fairly delocalized over both pentacenes and the bridging phenyl.

Molecular and Supramolecular Multiredox Systems

The design and synthesis of molecular and supramolecular multiredox systems have been summarized. These systems are of great importance as they can be employed in the next generation of materials for energy storage, energy transport, and solar fuel production. Nature provides guiding pathways and insights to judiciously incorporate and tune the various molecular and supramolecular design aspects that result in the formation of complex and efficient systems. In this review, we have classified molecular multiredox systems into organic and organic-inorganic hybrid systems. The organic multiredox systems are further classified into multielectron acceptors, multielectron donors and ambipolar molecules. Synthetic chemists have integrated different electron donating and electron withdrawing groups to realize these complex molecular systems. Further, we have reviewed supramolecular multiredox systems, redox-active host-guest recognition, including mechanically interlocked systems. Finally, the review provides a discussion on the diverse applications, e. g. in artificial photosynthesis, water splitting, dynamic random access memory, etc. that can be realized from these artificial molecular or supramolecular multiredox systems.

Subphthalocyanine-tetracyanobuta-1,3-diene-aniline conjugates: stereoisomerism and photophysical properties

Two subphthalocyanines (SubPcs) decorated at their peripheral (SubPc 1) or peripheral and axial (SubPc 2) positions with tetracyanobuta-1,3-diene (TCBD)-aniline moieties have been prepared as novel electron donor-acceptor (D-A) conjugates. In 1 and 2, the multiple functionalization of C 3-symmetric SubPcs by TCBD moieties, each of them having a chiral axis, results in the formation of several stereoisomers. Variable temperature 1H-NMR studies in chlorinated solvents suggest that these latter species, which are detected at low temperatures, rapidly interconvert - on the NMR timescale - into each other at room temperature. Beside their unique structural and stereochemical features, 1 and 2 present interesting physicochemical properties. Steady-state absorption and fluorescence, as well as electrochemical studies on 1 and 2 clearly point to an important degree of electronic communication between the SubPc, the TCBD and the aniline subunits. Moreover, in both derivatives, photoexcitation of the SubPc moiety yields charge transfer products involving the electron-rich SubPc moiety and the electron-withdrawing TCBD fragment. Interestingly, such polarized excited state species evolve in 1 and 2 in different ways. While in the former compound, it directly decays to the ground state, the fourth axial TCBD moiety in 2 leads to the formation of an intermediate fully charge separated state prior to the ground state deactivation.

Electronic Energy Transfer in a Subphthalocyanine-Zn Porphyrin Dimer Studied by Linear and Nonlinear Ultrafast Spectroscopy

The efficient harvesting and transport of visible light by electronic energy transfer (EET) are critical to solar energy conversion in both nature and molecular electronics. In this work, we study EET in a synthetic dyad comprising a visible absorbing subphthalocyanine (SubPc) donor and a Zn tetraphenyl porphyrin (ZnTPP) acceptor. Energy transfer is probed by steady-state spectroscopy, ultrafast transient absorption, and two-dimensional electronic spectroscopy. Steady-state and time-resolved experiments point to only weak electronic coupling between the components of the dimer. The weak coupling supports energy transfer from the SubPc to the zinc porphyrin in 7 ps, which itself subsequently undergoes intersystem crossing to populate the triplet state. The rate of the forward energy transfer is discussed in terms of the structure of the dimer, which is calculated by density functional theory. There is evidence of back energy transfer from the ZnTPP on the hundreds of picoseconds time scale. Sub-picosecond spectral diffusion was also observed and characterized, but it does not influence the picosecond energy transfer.

Intermolecular packing and charge transfer in metallofullerene/porphyrin cocrystals

Charge transfer in metallofullerene/porphyrin cocrystals is revealed for the first time.

Synergy of light harvesting and energy transfer as well as short-range charge shift reactions in multicomponent conjugates

We report herein on the design, the synthesis, and the characterization of a panchromatic, charge stabilizing electron donor-acceptor conjugate: (BBPA)₃-ZnPor-ZnPc-SubPc 1. Each component, that is, bis(biphenyl)phenylamine (BBPA), Zn(ii) porphyrin (ZnPor), Zn(ii) phthalocyanine ZnPc, and subphthalocyanine (SubPc), has been carefully chosen and modified to enable a cascade of energy and charge transfer processes. On one hand, ZnPor, has been functionalized with three electron-donating BBPA as primary and secondary electron donors and to stabilize the final charge-separated state, and, on the other hand, a perfluorinated SubPc has been selected as ultimate electron acceptor. In addition, the ZnPc unit contains several trifluoromethylphenyl moieties to match its energy levels to those of the other components. In fact, irradiation of the heteroarray 1 triggers a cascade of light harvesting across the entire visible range, unidirectional energy transfer, exergonic charge separating, and short-range charge shifting to afford in 14% quantum yield a (BBPA)₃˙⁺-ZnPor-ZnPc-SubPc˙^- charge-separated state. The lifetime of the latter reaches well into the range of tens of nanoseconds.

A DFT analysis of the ground and charge-transfer excited states of Sc3N@Ih-C80 fullerene coupled with metal-free and zinc-phthalocyanine

Endohedral metallofullerenes and phthalocyanine derivatives are recognized as excellent active materials in organic photovoltaics (OPVs). The tri-metallic nitride endohedral C80 fullerenes have greater absorption coefficients in the visible region and electron-accepting abilities similar to C60, which can allow for higher efficiencies in OPV devices. In this work, we have investigated the ground and charge transfer excited states of two co-facial donor-acceptor (D-A) molecular conjugates formed by the non-covalent coupling of trimetallic nitride endohedral fullerene (Sc3N@Ih-C80) with metal-free (H2Pc) and zinc-phthalocyanine (ZnPc) chromophores using DFT calculations. The charge transfer (CT) excitation energies are calculated using the perturbative delta-SCF method that enforces orthogonality between the ground and excited states. The binding energies calculated using the PBE and DFT-D3 methods indicate that the dispersion effects play an important role in the stabilization of these complexes. The ground state dipole moment of the Sc3N@C80-H2Pc dyad is much larger than that of Sc3N@C80-ZnPc, but this is reversed in the excited state where the dipole moment of Sc3N@C80-ZnPc increases significantly. The lowest few excitation energies in the gas phase for the two complexes are very close, in the range of 1.51-2.66 eV for Sc3N@C80-ZnPc and 1.51-2.71 eV for the Sc3N@C80-H2Pc complex. However, the lower ionization potential and lower exciton binding energy make the Sc3N@C80-ZnPc dyad a better candidate for OPVs as compared to the Sc3N@C80-H2Pc dyad.

Tri- and hexaferrocenyl-substituted subphthalocyanines in the quest for the optimum electron donor–acceptor distances

Three and six ferrocenyl subunits have been attached to the periphery of subphthalocyanines (SubPcs).

A Colorful Life: Scientific Achievements of Tomás Torres in the Fields of Phthalocyanines, Molecular Materials and Nanoscience

Some of the most important achievements of Tomás Torres in the last few decades within the fields of Phthalocyanines and related compounds, Molecular Materials and Nanoscience are revised and his recognized international prestige in these areas highlighted on the occasion of his 65th birthday.

A multicomponent molecular approach to artificial photosynthesis – the role of fullerenes and endohedral metallofullerenes

In this review article, we highlight recent advances in the field of solar energy conversion at a molecular level.

Supramolecular electron transfer-based switching involving pyrrolic macrocycles. A new approach to sensor development?

The potential utility of energy transfer in the design of pyrrolic macrocycle-based molecular switches and ability to serve as the readout motif for molecular sensors development is discussed.