Carmine Coluccini

Thiocyanate-free cyclometalated ruthenium sensitizers for solar cells based on heteroaromatic-substituted 2-arylpyridines

The first examples of thiocyanate-free thiophene-substituted Ru(II) cyclometalated complexes, based on thiophene-derived 2-(2,4-difluorophenyl)pyridine ligands, are presented and investigated as photosensitizers in DSCs. Upon thiophene substitution the complexes presented enhanced optical properties compared to the reference dye with no thiophene substitution. DSCs based on the dithienyl-derived dye showed power conversion efficiencies up to 5.7%, more than twice that containing the complex without the thiophene substitution.

Structurally-variable, rigid and optically-active D2 and D3 macrocycles possessing recognition properties towards C60.

The reactivity of aromatic dicarboxylic acids, in combination with an axially-chiral, suitable dibenzylic alcohol, derived from BINOL, has been exploited in one-pot esterification reactions for the direct formation of several rigid, homochiral macrocycles. Cyclic adducts possessing, respectively, average molecular D(2) and D(3) symmetries, have been characterized in pure forms, with isolated yields and selectivities which are substantially different from those rising from purely statistical arguments. NMR and CD spectroscopies detect the structural and shape variability in the scaffolds, reflected both in terms of large changes in chemical shifts of selected proton resonances, and in terms of the variation of the CD signature related to the dihedral angle defined by the binaphthyl units embedded in the rigid cyclic skeleton. The crystal structure of two homochiral D(2) macrocycles show the formation of ordered nanostructures in the solid state, with the naphthyl rings of the binaphthyl units packing intermolecularly in an eclipsed-like conformation to yield nonhelical tubular arrangements. The larger D(3) cyclic adducts are able to afford stable complexes with C(60) in toluene solution, with comparable binding strengths, yet whose stoichiometries are dependent on small variations in the spacing units and therefore in the shapes of the internal cavities of the cyclic structures.

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 Cu(2+), when compared with Zn(2+) and Ni(2+), 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 Cu(2+) using three different and potentially orthogonal techniques, namely UV, CD and fluorescence spectroscopies.

Synthesis, chiroptical and SHG properties of polarizable push–pull dyes built on π-extended binaphthyls

We report on new enantiopure binaphthyl derivatives in which electron-donating and electron-withdrawing substituents are placed in direct conjugation, to create active push–pull dyes for NLO applications. The dyes, unprecedentedly, extend their π-bridge from the 3,3′ positions of the binaphthyl units, and incorporate as acceptors pyridine units, possessing a coordinating nitrogen atom useful for further supramolecular polarization of the chiral dyes. The π-bridge is constructed by the sequential attachment of phenylenevinylene units to the enantiopure binaphthyl derivatives through Horner–Wadsworth–Emmons olefination, which proceed with high stereoselectivity, affording stereodefined chiral dyes. The polarization of the terminal pyridine units by means of labile complexation with Pd2+ ions has been demonstrated using both optical and chiroptical methods. The polarization by protonation can be made reversible in solution and solid state by exposure to ammonia vapors, as shown by absorption and emission spectroscopies. NLO properties, as determined by EFISH generation measurements in solution, are significant for the bisprotonated species when compared to previously reported binaphthyl substrates. TDDFT calculations show that the hyperpolarizability tensor contribution is responsible for enhancing SHG values upon protonation up to one order of magnitude, highlighting the potential of such ortho related, axially-chiral push–pull dyes for functional NLO applications.

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.

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.

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.