Giant Shape-Persistent Tetrahedral Porphyrin System: Light-Induced Charge Separation

Tetraphenylmethane appended with four pyridylpyridinium units works as a scaffold to self-assemble four ruthenium porphyrins in a tetrahedral shape-persistent giant architecture. The resulting supramolecular structure has been characterised in the solid state by X-ray single crystal analysis and in solution by various techniques. Multinuclear NMR spectroscopy confirms the 1 : 4 stoichiometry with the formation of a highly symmetric structure. The self-assembly process can be monitored by changes of the redox potentials, as well as by modifications in the visible absorption spectrum of the ruthenium porphyrin and by a complete quenching of both the bright fluorescence of the tetracationic scaffold and the weak phosphorescence of the ruthenium porphyrin. An ultrafast photoinduced electron transfer is responsible for this quenching process. The lifetime of the resulting charge separated state (800 ps) is about four times longer in the giant supramolecular structure compared to the model 1 : 1 complex formed by the ruthenium porphyrin and a single pyridylpyridinium unit. Electron delocalization over the tetrameric pyridinium structure is likely to be responsible for this effect

Non-phenomenological description of the time-resolved emission in solution with quantum-classical vibronic approaches-application to coumarin C153 in methanol

We report a joint experimental and theoretical work on the steady-state spectroscopy and time-resolved emission of the coumarin C153 dye in methanol. The lowest energy excited state of this molecule is characterized by an intramolecular charge transfer thus leading to remarkable shifts of the time-resolved emission spectra, dictated by the methanol reorganization dynamics. We selected this system as a prototypical test case for the first application of a novel computational protocol aimed at the prediction of transient emission spectral shapes, including both vibronic and solvent effects, without applying any phenomenological broadening. It combines a recently developed quantum–classical approach, the adiabatic molecular dynamics generalized vertical Hessian method (Ad-MD (Formula presented.) VH), with nonequilibrium molecular dynamics simulations. For the steady-state spectra we show that the Ad-MD|gVH approach is able to reproduce quite accurately the spectral shapes and the Stokes shift, while a ∼0.15 eV error is found on the prediction of the solvent shift going from gas phase to methanol. The spectral shape of the time-resolved emission signals is, overall, well reproduced, although the simulated spectra are slightly too broad and asymmetric at low energies with respect to experiments. As far as the spectral shift is concerned, the calculated spectra from 4 ps to 100 ps are in excellent agreement with experiments, correctly predicting the end of the solvent reorganization after about 20 ps. On the other hand, before 4 ps solvent dynamics is predicted to be too fast in the simulations and, in the sub-ps timescale, the uncertainty due to the experimental time resolution (300 fs) makes the comparison less straightforward. Finally, analysis of the reorganization of the first solvation shell surrounding the excited solute, based on atomic radial distribution functions and orientational correlations, indicates a fast solvent response (≈100 fs) characterized by the strengthening of the carbonyl–methanol hydrogen bond interactions, followed by the solvent reorientation, occurring on the ps timescale, to maximize local dipolar interactionsThis research was funded by ICSC—Centro Nazionale di Ricerca in High Performance Computing, Big Data and Quantum Computing, funded by European Union—NextGenerationEU— PNRR, Missione 4 Componente 2 Investimento 1.4 (F.S and G.P); MICINN Project PID2019-110091GBI00 (JC); H2020-LC-SC3-2020-RES-RIA-101006839 project “CONDOR” and MUR-PNRR (NEST— Network 4 Energy Sustainable Transition, Estended Partnership—PE000002 (SG, BV and NA

The electronic properties of a homoleptic bisphosphine Cu(I) complex: a joint theoretical and experimental insight

The origin of the optical properties of the firstly reported stable luminescent [Cu(PP)_2]^+ complex [Cu(dppb)_2]+ [dppb = 1,2-bis(diphenylphosphino) benzene] is investigated using the exchange-correlation functional PBE0. The choice of the basis set used is discussed and a comparison with the results obtained by other functionals is performed. The role played by the bisphosphine ligands within the complex is elucidated by considering the electronic properties of the ligand alone to evidence how both the geometrical changes and the electronic interactions, induced by the inclusion of the metal cation, affect the electronic behavior of the whole system. The NBO analysis shows how the aryl groups of the ligands act as a reservoir of electrons within the complex. The electronic excitations of both the complex and of the ligand, calculated by including the solvation effects, allow to assign the lowest energy absorption broad band, recorded in CH_2Cl_2 solution. The peculiar contribution of the phosphorus atoms to the description of the high occupied MOs and the participation of the copper cation to the description of the lowest singlet excited state, is pointed out. The origin of the observed phosphorescence of the complex is attributed to a triplet state, whose SOMO is characterized by the contributions of the valence 4s and of the Rydberg 5s AOs of the metal cation, along with the lone pair orbitals of the P atoms.Si sono studiate le proprieta` ottiche del primo complesso stabile e luminescente di tipo [Cu(PP}]^+ [[Cu(dppb)$_2]^+$ [dppb = 1,2-bis(difenilfosfino) benzene], riportato in letteratura utilizzando il metodo PBE0. Si e` discussa la scelta della base orbitale utilizzata nello studio e si e` effettuato un confronto con altri metodi DFT. Si e` illustrato il ruolo dei leganti bisfosfinici nel complesso esaminando come cambia la loro geometria e configurazione elettronica con l\u27inclusione del metallo per formare il complesso. Sono state studiate le eccitazioni elettroniche del complessso e del legante includendo gli effetti di solvatazione. per assegnare la prima banda di assorbimento osservata negli spettri con i campioni in soluzioni di diclorometano. Sono stati evidenziati i contributi dell\u27atomo di fosforo alla descrizione degli orbitali occupati ad alta energia del complesso e del Cu^+ a quelli virtuali a piu` bassa energia. L\u27origine della fosforescenza del complesso e` attribuita ad uno stato di tripletto il cui SOMO e` caratterizzato dagli orbitali atomici di valenza di tipo 4s e da un orbitale di Rydberg 5s di Cu^+ e dagli orbitali atomici singolarmente occupati del fosforo

[60]Fullerene\u2013porphyrin [n]pseudorotaxanes: self-assembly, photophysics and third-order NLO response

By means of different spectroscopic techniques, we investigate a novel series of porphyrin derivatives (H2TPP), connected to dibenzo-24-crown-8 (DB24C8) moieties, which undergo self-assembly with different methano[60]fullerene units bearing dibenzylammonium (DBA) cations. The formation of both [2] and [3]pseudorotaxanes was proved by means of NMR, UV-Vis-NIR absorption and emission spectroscopies. With the support of molecular modelling studies, spectroscopic investigations showed the presence of a secondary interaction between the porphyrin and the C60 chromophores leading to the formation of different types of \u2018\u2018face-to-face\u2019\u2019 assemblies. Remarkably, investigations of the non-linear optical response of these supramolecular systems showed that individual porphyrin and fullerene derivatives exhibit significantly lower second hyperpolarizability values when compared to their pseudorotaxanes functionalised counterparts. This proves that this class of supramolecular materials possesses relevant NLO response, which strongly depends on the structural arrangement of the chromophores in solution. Introductio

Solvent Molding of Organic Morphologies Made of Supramolecular Chiral Polymers

12sihe self-assembly and self-organization behavior of uracil-conjugated enantiopure (R)- or (S)-1,1'-binaphthyl-2,2'-diol (BINOL) and a hydrophobic oligo(p-phenylene ethynylene) (OPE) chromophore exposing 2,6-di(acetylamino)pyridine termini are reported. Systematic spectroscopic (UVvis, CD, fluorescence, NMR, and SAXS) and microscopic studies (TEM and AFM) showed that BINOL and OPE compounds undergo triple H-bonding recognition, generating different organic nanostructures in solution. Depending on the solvophobic properties of the liquid media (toluene, CHCl3, CHCl3/CHX, and CHX/THF), spherical, rod-like, fibrous, and helical morphologies were obtained, with the latter being the only nanostructures expressing chirality at the microscopic level. SAXS analysis combined with molecular modeling simulations showed that the helical superstructures are composed of dimeric double-cable tape-like structures that, in turn, are supercoiled at the microscale. This behavior is interpreted as a consequence of an interplay among the degree of association of the H-bonded recognition, the vapor pressure of the solvent, and the solvophobic/solvophilic character of the supramolecular adducts in the different solutions under static and dynamic conditions, namely solvent evaporation conditions at room temperature.partially_openopenĐorđević, Luka; Marangoni, Tomas; Miletić, Tanja; Rubio-Magnieto, Jenifer; Mohanraj, John; Amenitsch, Heinz; Pasini, Dario; Liaros, Nikos; Couris, Stelios; Armaroli, Nicola; Surin, Mathieu; Bonifazi, DavideĐorđević, Luka; Marangoni, Tomas; Miletic, Tanja; Rubio Magnieto, Jenifer; Mohanraj, John; Amenitsch, Heinz; Pasini, Dario; Liaros, Nikos; Couris, Stelios; Armaroli, Nicola; Surin, Mathieu; Bonifazi, David

Calix[4]arene-Linked Bisporphyrin Hosts for Fullerenes: Binding Strength, Solvation Effects, and Porphyrin−Fullerene Charge Transfer Bands

A calix[4]arene scaffolding has been used to construct bisporphyrin ("jaws" porphyrin) hosts for supramolecular binding of fullerene guests. Fullerene affinities were optimized by varying the nature of the covalent linkage of the porphyrins to the calixarenes. Binding constants for C60 and C70 in toluene were explored as a function of substituents at the periphery of the porphyrin, and 3,5-di-tert-butylphenyl groups gave rise to the highest fullerene affinities (26,000 M(-1) for C60). The origin of this high fullerene affinity has been traced to differential solvation effects rather than to electronic effects. Studies of binding constants as a function of solvent (toluene < benzonitrile < dichloromethane < cyclohexane) correlate inversely with fullerene solubility, indicating that desolvation of the fullerene is a major factor determining the magnitude of binding constants. The energetics of fullerene binding have been determined in terms of DelatH and DeltaS and are consistent with an enthalpy-driven, solvation-dependent process. A direct relationship between supramolecular binding of a fullerene guest to a bisporphyrin host and the appearance of a broad NIR absorption band have been established. The energy of this band moves in a predictable manner as a function of the electronic structure of the porphyrin, thereby establishing its origin in porphyrin-to-fullerene charge transfer

Light-Induced Processes in Fullerene Multicomponent Systems in Fullerenes Principles and Applications

Light-Induced Processes in Fullerene Multicomponent System