acentric nanostructured assembly as a strategy for the design of organic electrooptic materials

The rational utilization of the paradigms of self-assembly and self-organization, essential requisites for the building up of the architectural complexity found in natural systems, is becoming an unavoidable strategy in the world of nanosciences. Recent developments in the field of organic materials for second-order nonlinear optics have focused in the recent past not only towards the optimization of the molecular engineering translating into ultrahigh molecular hyperpo- larizabilities, but also, and more fundamentally, towards the realization of acentric assemblies of such chromophores into nanomaterials with high electrooptic responses. Selected, recent examples dealing with these concepts are discussed

Synthesis of binaphthyl-based push-pull chromophores with supramolecularly polarizable acceptor ends

We report on the design and synthesis of new enantiopure binaphthyl derivatives in which electron-donating and electron-withdrawing substituents are placed in direct conjugation, to create push-pull dyes potentially active for NLO applications. The dyes, unprecedentedly, extend their π-bridge from the 3,3′ positions of the binaphthyl units and incorporate as acceptors 1,3-dicarbonyl and tetrafluorobenzene units, useful for further supramolecular polarization of the chiral dyes

Conformational Studies by Dynamic NMR. 100. Enantiomerization Process of Stereolabile Atropisomers in Pyridine-Substituted Adamantane Derivatives.

CAN 141:224907 AN 2004:566825 CAPLUS (COPYRIGHT (C) 2008 ACS ON SCIFINDER (R)) ABSTRACT THE BARRIERS FOR INTERCONVERTING THE CONFORMATIONAL ENANTIOMERS (STEREOLABILE ATROPISOMERS) OF PYRIDINE-SUBSTITUTED ADAMANTANE DERIVS. HAVE BEEN DETD. BY DYNAMIC 13C NMR SPECTROSCOPY. THE TREND OF THESE VALUES PARALLELS THAT ANTICIPATED BY MM CALCNS. IN AT LEAST ONE CASE, THE COMPUTED STRUCTURE WAS FOUND TO AGREE WITH THAT OBTAINED BY SINGLE-CRYSTAL X-RAY DIFFRACTION. IN ADDN., IT HAS BEEN POSSIBLE TO ACHIEVE A PHYS. SEPN. OF A PAIR OF THESE STEREOLABILE ATROPISOMERS AT -60 °C BY MEANS OF THE ENANTIOSELECTIVE CRYOGENIC HPLC TECHNIQUE

Quaterpyridine Ligands for Panchromatic Ru(II) Dye Sensitizers

A new general synthetic access to carboxylated quaterpyridines (qpy), of interest as ligands for panchromatic dyesensitized solar cell organometallic sensitizers, is presented. The strategic step is a Suzuki−Miyaura cross-coupling reaction, which has allowed the preparation of a number of representative unsubstituted and alkyl and (hetero)aromatic substituted qpys. To bypass the poor inherent stability of 2-pyridylboronic acid derivatives, we successfully applied N-methyliminodiacetic acid (MIDA) boronates as key reagents, obtaining the qpy ligands in good yields up to (quasi)gram quantities. The structural, spectroscopic (NMR and UV−vis), electrochemical, and electronic characteristics of the qpy have been experimentally and computationally (DFT) investigated. The easy access to the bis-thiocyanato Ru(II) complex of the parent species of the qpy series, through an efficient route which bypasses the use of Sephadex column chromatography, is shown. The bis-thiocyanato Ru(II) complex has been spectroscopically (NMR and UV−vis), electrochemically, and computationally investigated, relating its properties to those of previously reported Ru(II)−qpy complexes.“This document is the Accepted Manuscript version of a Published Work that appeared in final form in [The Journal of Organic Chemistry], copyright © American Chemical Society after peer review and technical editing by the publisher

From red to blue shift: switching the binding affinity from the acceptor to the donor end by increasing the π-bridge in push–pull chromophores with coordinative ends

A series of homologous push–pull compounds, in which identical donor (a dimethylamino) and acceptor (a malonate ester) functionalities endcap crescent PPV fragments, exhibit striking differences in their supramolecular recognition of cations acting as Lewis acids. The shorter conjugated compound (one phenyl ring) coordinates a wide variety of lanthanide cations (Eu3+, Yb3+ and Er3+) in MeCN solutions to the 1,3-dicarbonyl acceptor end, resulting in an overall supramolecular polarization of the system (red shift of the intramolecular charge-transfer ICT band). With the “hard” cation Sc3+, recognition switches to the tertiary amine donor end, turning the conjugated system from D–π–A to A–π–A, and resulting in a blue shift of the ICT band upon complexation. Interestingly, increasing the conjugation by means of the insertion of sequential p-phenylenevinylene units into the ligand results in coordination to the donor end regardless of cation “hardness” (Sc3+, Eu3+ and Er3+), suggesting a relative change in the nucleophilicity of the two coordinating ends when increasing the length of the conjugated π-bridge. Such a hypothesis is supported by quantum chemical calculations on the ligands and subsequent atomic charges determination using two independent approaches (QTAIM and CHelpG). The characterization of the thermodynamic stabilities and the dimensionalities of the ligand–cation complexes in solution reveals striking differences from case to case, yet increasing affinities (from log Kav = 2.5 to log Kav = 4.9) are recorded with the increase of the π-conjugated bridge

Locked Chromophores as CD and NMR Probes for the Helical Conformation of Tetraamidic Macrocycles

A series of tetraamidic homochiral macrocycles have been built convergently upon the introduction in the covalent scaffold of two 1,1-binaphthyl-2,2-diol derivatives, joined by aromatic spacers of differing shapes and rigidity (p-phenyl, 4,4-biphenyl, 3,3-biphenyl) through aromatic amide functionalities, perfectly positioned to intramolecularly hydrogen bond the naphtholic oxygen acceptors of the binaphthyl units, in order to effectively lock the central chromophores in spatial proximity. The combination of several techniques, namely NMR and CD spectroscopies, and computational modeling, allows for a clear depiction of the structure and conformation of the macrocycles in solution. In the case of the shape unstable 3,3-biphenyl spacer, the preferred conformation of a wrapped form in a relatively polar (EtOH) solvent is clearly signalled by CD spectroscopy by analyzing the changes in the shape of the induced CD signal deriving from the central, achiral chromophore absorption band. The rigid, covalent scaffold in which the two central 3,3-biphenyl spacers are embedded raises the energetic barrier for the rotation around the aryl–aryl bonds of the spacers to a value (8.0 kcal mol-1) much higher than the value calculated in the case of unlocked biphenyls

Chemoselective Functionalization of 3,3'-Substituted BINOL Derivatives

An efficient chemoselective differentiation of vicinal phenolic and benzylic alcohols on optically active binaphthyl skeletons has been achieved via TBS protection of the less sterically hindered, external 3,3' benzylic positions. Further manipulation of functionalities either in the 2,2' or 3,3' positions is then easily achieved in high yields via the use of BOC protecting groups, functioning orthogonally to TBS

A Chiral Probe for the Detection of Cu(II) by UV, CD and Emission Spectroscopies

The synthesis and characterization of the new chiral ligand 2, based on a BINOL-tren (tren = tris(2-aminoethyl) amine) conjugate, in enantiomerically pure form, are reported. UV-Vis spectrophotometric and spectrofluorimetric studies at variable pH show that the incorporation of a phenolic functionality in close proximity to the polyamino fragment of the molecule causes a dramatic variation of the acid-base and coordination properties of the molecule; the major role of this functionality in determining the selectivity observed in the complexation of Cu2+, when compared with Zn2+ and Ni2+, at pH = 5 in aqueous MeOH, has been clarified, also by comparison with the spectroscopic and coordination properties of model compound 3, bearing protected OMe functionalities. The peculiar absorbance, emission and chiroptical properties of the binaphthyl fragment incorporated in compound 2 can be used for the selective detection of Cu2+ using three different and potentially orthogonal techniques, namely UV, CD and fluorescence spectroscopies