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

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

New [1]benzothieno[3,2- b]benzothiophene-tetraoxide-based TADF emitters with a D–A–D structure for OLED applications

Luminescent organic molecules showing thermally activated delayed fluorescence (TADF) are appealing materials for high-efficiency OLEDs. Here, we report a new class of organic luminescent materials with TADF properties, and a D–A–D electronic structure based on [1]benzothieno[3,2-b]benzothiophene-tetraoxide BTBTOx4 as the acceptor unit A. Three donor units D were selected and coupled with BTBTOx4, using a straightforward synthetic protocol based on microwave-assisted Buchwald–Hartwig cross-coupling, to yield three organic luminescent molecules labelled PTz2-BTBTOx4, MPA2-BTBTOx4 and POCz2-BTBTOx4. Chemico-physical and structural properties were investigated by cyclic voltammetry, electrical measurements, crystallographic analysis, theoretical study and photophysical characterization. All three emitters showed high electrochemical stability with reversible oxidation waves. MPA2-BTBTOx4 was selected as the reference molecule for X-ray analysis, which revealed torsion angles of −59° and 86° between the donor (MPA) and acceptor (BTBTOx4) units supporting their appropriate structural configuration to have TADF properties. Photophysical studies highlighted a noteworthy increase in PL efficiency upon deoxygenation for all three compounds. The oxygen-induced quenching of delayed fluorescence and time-resolved photoluminescence studies supported the presence of the TADF properties, further corroborated for PTz2-BTBTOx4 and MPA2-BTBTOx4 by DFT studies. Preliminary steady-state photophysical studies were also carried out on neat films of all three emitters, revealing a pronounced self-quenching of photoluminescence for PTz2-BTBTOx4 and MPA2-BTBTOx4 and a minimal self-quenching for POCz2-BTBTOx4, which maintains a high ΦPL (22%) comparable to that in Zeonex and half of that in PMMA. As a proof of concept, the three emitting molecules were tested as neat films in simple-structure OLED devices. In accordance with the photoluminescence data, POCz2-BTBTOx4, thanks to its sterically bulky structure, retains a good emission capacity even in a neat film and was also selected as an active matrix to build OLED devices by using two different deposition techniques: inkjet-printing and spin coating

Neuroimaging in cluster headache and other trigeminal autonomic cephalalgias

The central nervous system mechanisms involved in trigeminal autonomic cephalalgias, a group of primary headaches characterized by strictly unilateral head pain that occurs in association with ipsilateral craniofacial autonomic features, are still not comprehensively understood. However, functional imaging methods have revolutionized our understanding of mechanisms involved in these primary headache syndromes. The present review provides a brief overview of the major modern functional neuroimaging techniques used to examine brain structure, biochemistry, metabolic state, and functional capacity. The available functional neuroimaging data in cluster headache and other TACs will thus be summarized. Although the precise brain structures responsible for these primary headache syndromes still remain to be determined, neuroimaging data suggest a major role for posterior hypothalamus activation in initiating and maintaining attacks. Furthermore, pathophysiological involvement of the pain neuromatrix and of the central descending opiatergic pain control system was observed. Given the rapid advances in functional and structural neuroimaging methodologies, it can be expected that these non-invasive techniques will continue to improve our understanding into the nature of the brain dysfunction in cluster headache and other trigeminal autonomic cephalalgias

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

Light-Induced Processes in Fullerene Multicomponent System

Novel phenanthroline ligands and their kinetically locked copper(I) complexes with unexpected photophysical properties

The new, sterically encumbered phenanthroline ligands 1a,b, both characterized by the presence of bulky aryl substituents (3,5-di-tert-butyl-4- methoxyphenyl, 2,4,6-trimethylphenyl) in the 2,9-position, were prepared along with their homoleptic [Cu(1a,b)2]+ and heteroleptic complexes [Cu(1a,b)(phen)]+ (phen = parent 1,10-phenanthroline). Due to the pronounced steric shielding, particularly effective in ligand 1a, the formation of the homoleptic complex [Cu(1a)2]+ becomes very slow (5 days). Once formed, the homoleptic complexes [Cu(1a,b) 2]+ do not exchange ligands even with phen added in excess because they are kinetically locked due to the large tert-butylphenyl substituents at the phenanthroline unit. The electronic absorption spectra of the homoleptic complexes [Cu(1a)2]+ and [Cu(1b) 2]+ evidence a strongly different ground state geometry of the two compounds, the former being substantially more distorted. This trend is also observed in the excited-state geometry, as derived by emission spectra and lifetimes in CH2Cl2 solution. The less distorted [Cu(1b)2]+, compared to [Cu(1a)2]+, is characterized by a 15- and over 100-fold stronger emission at 298 and 77 K, respectively. Noticeably, the excited-state lifetime of [Cu(1a) 2]+ in solution is unaffected by the presence of molecular oxygen and only slightly shortened in nucleophilic solvents. This unusual behavior supports the idea of a complex characterized by a "locked" coordination environment. © 2006 American Chemical Society