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Self-Organization of Polar Porphyrinoids [ChemPlusChem]
[October 28, 2014]

Self-Organization of Polar Porphyrinoids [ChemPlusChem]


(ChemPlusChem Via Acquire Media NewsEdge) This Minireview focuses on the very recent developments in the field of porphyrin-based self-assembled nanomaterials with a particular focus on the use of tetrapyrrolic macrocycles bearing amphiphilic and ionic functionalities. As one of the most studied molecular materials, the importance of porphyrin-derived nanomaterials has attracted wide interest in many applications like catalysis, photodynamic therapy, and organic solar cells to name a few. By using key examples that have recently appeared in the literature, the discussion unfolds through two sections: amphiphilic and ionic assemblies. Although it focuses on the nanostructuring methodologies used to obtain organized materials, the discussion will also target the physical characterization of the functional materials for their implementation in prototypes.



Keywords: macrocycles · nanostructures · porphyrinoids · self-assembly · supramolecular chemistry Introduction Photosynthesis has always been a motivation for researchers seeking to understand fundamental natural processes by de- signing simpler molecular mimics.[1] In this context, under- standing and mimicking the role of chlorophylls as light-har- vesting antennae to collect photons and to efficiently transfer energy to the reaction center has recently attracted great at- tention.[1a, 2] However, owing to the presence of two or more saturated carbon atoms, the chemical synthesis and modifica- tion of such macrocyclic scaffolds is less accessible for engi- neering artificial photosynthetic systems.[3a] Synthetically acces- sible structures such as fully conjugated tetrapyrrolic macrocy- cles, that is, porphyrins, were revealed to be better candidates to replace chlorins and their congeners for mimicking natural photosynthesis despite the fact that their Q-bands are weak and the excitonic coupling not as strong as that required for fast exciton migration.[3b] Hence, enormous efforts have been devoted to the design of porphyrins that undergo self-assem- bly into nanostructures featuring unique spectral characteris- tics like those of chlorophylls in natural systems.[3] Specifically, self-organization into J-aggregates is of particular interest as organic materials displaying highly favorable exciton migration and 2D percolation pathways for both hole and electron charge carriers feature this arrangement.[4] Similar to naturally occurring conjugated heteroaromatic chlorophyll macrocycles, porphyrins exhibit a very intense light-absorption profile, accessible oxidation and reduction po- tentials, fast energy and/or electron-transfer donor abilities, and so forth.[3, 5] Porphyrins serve as unique molecular compo- nents in technologies such as sensors, photonics, electronics, and catalysts.[5, 6] All this has prompted an enormous interest in developing new synthetic methodologies[1b, 7] and self-assem- bly protocols[2a, 8-11] for engineering functional porphyrin-based materials, in which the tetrapyrrolic macrocycles are organized into J-aggregates.

Among the different approaches, the use of noncovalent in- teractions for governing the structural properties of porphyrin- based materials is certainly the most versatile and exploited.[12] Among the different tetramacrocyclic derivatives, amphiphilic porphyrins self-assemble under diverse conditions to form exotic nanostructures.[13, 14] Another important strategy is based on the exploitation of ionic interactions to order porphyrinoids. In this context, much effort has been devoted to the synthesis and self-organization of amphiphilic and ionic porphyrins. The present Minireview addresses the very recent advancements, exclusively from 2010 onwards in the area of amphiphilic and ionic self-assemblies of porphyrins.


Amphiphilic Self-Assembly In supramolecular assemblies, the controlled balance between two competing interactions has been regarded as one of the successful methods for creating nanostructures.[13] The subtle balance between hydrophilic and hydrophobic interactions, provided by programmed molecular structures, has resulted in various supramolecular materials featuring structure-depen- dent properties.[15] Amphiphilicity can be defined by the way in which molecules arrange themselves to form initial layered assemblies through a hydrophobic and hydrophilic balance of the structural properties, which in turn lead to diverse hier- archical supramolecular assemblies. The versatility and tunabili- ty of the structure of organic molecules allowed the amphiphil- ic approach to become a widely used method to engineer con- trolled supramolecular nanostructures.[13c, 15] In this section, we describe the very recent studies dealing with amphiphilic por- phyrin conjugates.

In a recent report, Numata et al. described the formation of droplet-templated morphologies using amphiphilic zinc chlorin (ZnChl) 1 (Figure 1) bearing a dendritic tetra(ethylene glycol) (TEG) unit and an isonicotinic acid moiety appended on the chlorophyll ring.[16] In a water/tetrahydrofuran (THF) mixture, modified chlorophyll 1 undergoes self-assembly through effec- tive ZnII-pyridine coordination interactions to form one-dimen- sional rodlike structures, with a characteristic redshift for the Soret and Q electronic transitions from 424 to 447 nm and from 651 to 668 nm, respectively, followed by a dramatic in- crease in the circular dichroism (CD) signal intensity (Figure 1).

In a ClCH2CH2Cl (DCE)/water emulsion, ZnChl amphiphile 1 perpendicularly organizes at the interface between the two immiscible liquid phases, guided by the strong water solvation of the hydrophilic TEG tails. As the concentration increases, the morphology of the nanostructures changes from a spherical to a multilayer tubular structure (Figure 1), with the former shape templated by the DCE droplets dispersed in the aqueous solu- tions. The hydrophobic environment within the tubes has been effectively exploited to trap guest functional molecules such as cyanine dye. A decrease in the fluorescence intensity of the cyanine dye at 568 nm and appearance of a new peak at 668 nm deriving from the chlorophyll unit indicated possible energy transfer from the entrapped dye to the chlorophyll.

Simultaneously, the group of Wrthner engineered microme- ter-sized nanotubes in water by using modified ZnChl bearing hydrophilic dendron wedges (molecule 2a, Figure 2a).[17a,b] Ex- ceptionally, the aggregates exhibited extraordinary stability in solution owing to the ideal interface provided by the TEG chains as shown by the transmission electron microscope (TEM) and cryo-TEM imaging techniques, which indicated the clear formation of isolated indi- vidual and bundled nanorods, respectively (Figure 2b, c). An in- trinsic charge-carrier mobility of 0.03 cm2 V1 s1 was observed for the morphologies of 2a in the solid state. In addition, pulse-ra- diolysis time-resolved microwave conductivity (PR-TRMC) indicated great thermally activated charge- carrier mobility in the tempera- ture range between 25 and 100 8C. The high charge-carrier mobilities of the tubular mor- phologies are attributed to the maximized overlap between the ZnChl monomers within the ag- gregates through p-p stacking interactions. Conductive atomic force microscopy (AFM) investi- gations have also been used to study the transport of charges along individual nanowires and an exceptionally high conductivi- ty value of (0.480.07) Sm1 for a 6 nm-wide wire was measured. A clear correlation between charge-transport properties and self-assembled nanostructures of ZnChls 2b,c in the solid state have been investigated by PR- TRMC measurements.[18a] The one-dimensional (1D) tubular as- semblies of 2b exhibited efficient charge-transport mobilities (0.07 cm2 V1s1 for 31-hydroxy ZnChls), whereas the corre- sponding 31-methylated derivative (31-methoxy ZnChls) fol- lowed a two-dimensional brickwork-type slipped-stack ar- rangement with a charge mobility of about 0.28 cm2 V1 s1. The noncovalent rodlike structures formed by multichromo- phoric dyads of chlorin and naphthalene diimide (NDI), be- haved as light-harvesting antennae.[18b] An efficient energy transfer was observed from the enveloped NDI to the inner ZnChl backbone, upon selective photoexcitation of the former.

Ariga et al. reported the self-assembly of trigeminal porphyr- ins 3a,b (Figure 3) to form nanowires.[19] Thick-walled microtu- bules were formed upon addition of 3a into a CH2Cl2/MeOH mixture, whereas spherical particles were obtained with conju- gate 3b (as hollow capsules in the precipitate and thin-walled vesicles in the supernatant solution). However, an aligned pat- tern of nanowires was obtained when a solution of porphyrin 3b in CH2Cl2/MeOH was deposited on a mica surface (Fig- ure 3a). Each nanowire exhibited a consistent height of 3.2 nm and width of 8.5 nm, in line with the strong interaction of the hydrophilic ethylene glycol groups with the hydrated mica substrate keeping the hydrophobic n-dodecyl chains normal to the surface (see schematic representation in Figure 3b). De- tailed AFM investigations revealed that both substituents, that is, the flexible tripodal amphiphilic and the Br functions, are the basic structural requirements for nanowire formation. The detailed AFM analyses have indicated that the nanowires formed on the mica substrate could be broken or its growth could be stimulated through scratching of the already formed nanowires. Hence, sequential erasure/regrowth processes could lead to the formation of new nanowire structures.

Bhosale et al. investigated the solvent-dependent self-assem- bly of protoporphyrin 4a functionalized with triethylene glycol chains.[20a] The presence of triethylene glycol drives mole- cule 4a to selectively form two different nanosized spherical aggregates in different solutions. Upon addition of cyclohex- ane (C6H12) to a solution of CHCl3, steady-state visible-absorp- tion measurements displayed the appearance of broad and asymmetric absorption bands due to aggregation phenomena. AFM and TEM images clearly demonstrated that in the C6H12/ CHCl3 solution (10:1 v/v), amphiphile 4aforms uniform multila- mellar microvesicles with an average diameter of approximate- ly 65 nm and a membrane thickness of 2.5-3 nm. As shown in Figure 4a, bilayer vesicles, in which the polyether chains form the main body and the porphyrin append is exohedrally ex- posed, are formed. In a CHCl3/MeOH solution, protoporphyrin 4a forms micellar aggregates with smaller diameters and heights of approximately 6 nm.

Another protoporphyrin amphiphile bearing hydrophobic (alkyl) and hydrophilic (glycol) solubilizing chains, 4b, has been prepared by double-cross metathesis using second-generation Grubb's catalyst.[20b] A tunable assembly formation has been achieved by taking advantage of the solvophobic character of the side chains. Interestingly, the aggregation of protoporphyin 4b resulted in wormlike fibrils and nanoparticles (50-60 nm di- ameter) when obtained from a solution of CHCl3/MeOH (1:1, v/ v) and CHCl3/MeOH (1:9, v/v), respectively. Protoporphyrin de- rivative 5 bearing linear alkyl chains equipped as minidendrons also behaved as an amphiphile to form rodlike nanostructures in a C6H12/CHCl3 mixture and a honeycomb-like morphology in DMSO.[20c] The morphological transformation is most likely con- trolled by the solvent composition, lamellar-phase p stacking of the porphyrin and by the change of the hydrogen-bonding and van der Waals interactions.

A peptide amphiphile c16-AHL3K3-CO2H, containing a histi- dine unit to bind Zn protoporphyrin 6 has been also report- ed.[21] The b-sheet structure of the peptide allows the porphy- rin unit to adopt a perfect organization. The presence of red- shifted B- and Q-bands of the porphyrin in the UV/Vis spec- trum and a strong exciton-coupled CD signal in the visible region clearly indicated the his- tidyl axial binding of the chro- mophore in the presence of NH4OH. The peptide acts as a light-harvesting fiber with por- phyrin 6 and an oxygen-activat- ing fiber with a reduced hemin.

Aggregation of porphyrin de- rivatives 7a,b bearing steroidal moieties further conjugated with glucosyl groups in the meso po- sition led to supramolecular chiral architectures in a dimethyl acetamide (DMAc)/water mix- ture.[22] The overall chirality of the architectures is controlled by the structure of the steroidal moieties. In addition, long fi- brous networks and smaller rods formed by the coalescence of smaller globular structures could be also obtained at lower (0.8 mm) and higher (2.4 mm) concentrations of 7a in DMAc/ H2O (87:13). For protoporphyrin 7b, the least CD-active, nano- particle-like random aggregates were formed under the same conditions as those used for nanostructuring molecule 7a. The observed differences in the CD intensity for molecules 7a and 7b are attributed to the strong interchromophoric aromatic in- teractions. Moreover, aggregates of 7a formed a coagulated gel owing to the synergic effect of both cholesterol and sugar moieties.

By exploiting 1,3-dipolar cycloaddition reactions, nonlipid- type p-electronic amphiphile 8 (Figure 5), consisting of a por- phyrin-fullerene dyad appended to triethylene glycol chains, in aqueous media forms uniformly sized stable and robust multilamellar vesicles.[23a] A modified racemic mixture of dyad 9 (Figure 5) also self-assembles to form spherical morphologies exhibiting very poor photoconductivity in the I-V profile of its casted film.[23b] But enantiopure dyad 9 formed photoconduc- tive nanofibers with an optimum donor-accepter (D/A) orien- tation. The suspension in CH2Cl2/MeOH solution displayed a broad Soret band with a redshifted shoulder having a highly enhanced split Cotton effect, which is significantly different from that obtained with racemate 9. This points to an efficient exciton coupling in the organized structure. Ambipolar charge transport was observed for the nanofibers in the time-of-flight measurement under positive and negative electric fields upon photoexcitation with a 355 nm laser pulse. The hole (mh) and electron (me) mobility values of the nanofibers were found to be 0.08 and 0.06 cm2 V1 s1, respectively. The nanofibers of enantiopure molecule 9 showed intrinsic charge-carrier mobili- ty with one order of magnitude higher than that measured for the spherical morphologies formed by the racemate molecule.

The main difference in dyads 9-11 is the linker parts con- necting the porphyrin to the fullerene moieties.[23c] In contrast to the nanofibers formed by enantiopure dyad 9, self-assembly of molecules 10 and 11 yielded nanotubular assemblies (Figure 5). Morphologies of molecule 10 are formed by a coaxial donor-acceptor assembly in which the fullerene moieties are localized in the inner part of the structure as clusters coated by layers of J-type aggregated porphyrin derivatives (Figure 5a). The inner and outer surfaces of the nanotube are decorated with hydrophilic glycol chains. In the case of molecule 11, the dyad adopts a tilted orientation in which the porphyrin and the fullerene moieties stack with an alternate geometry (Figure 5b). The TRMC (fSmmax) value of nanotubes formed from mole- cule 10 (1.02103 cm2V1s1) was found to be 6.5-fold greater than that obtained from nano- structures solely formed by 11 (0.16103 cm2V1s1).

The Langmuir-Blodgett tech- nique has been used to create unidirectionally aligned photo- conductive porphyrin-C60 heter- ojunction molecular wires.[24] Amphiphilic porphyrin-C60 dyad 12, with tapered hydrophilic glycol units, forms molecular wires through J-type aggrega- tion of the porphyrin appendag- es, by the p-p stacking interac- tions between C60 and intermo- lecular hydrogen-bonding con- tacts between glycol chains (Figure 6a). The AFM image (Fig- ure 6b) showed that the molecu- lar wires are composed of unidir- ectionally aligned triangular blocks. These triangular units re- sulted from the adjacent stack- ing of trigonal packed fullerenes and the conelike hydrophilic chains under surface pressure. In addition, the unidirectionally aligned wires display robust pho- tocurrent properties upon illumination with white light.

Ionic Self-Assemblies As one of the successful strat- egies in crafting supramolecular architectures, ionic interactions recently attracted deep inter- est.[25] The electrostatic attraction between oppositely charged ionic species has provided room for tunable assemblies.[25b] The electrostatic interaction drives the molecules to form unique solvo-selective structures, aided by p-p stacking between the porphyrin cores.

Parquette and co-workers re- ported the self-assembly of bo- laamphiphile 13 into nanotubes composed of electron-donor and -acceptor units resulting in het- erojunctions.[26] The strong J- type p-p interactions in 10 % MeOH/H2O solutions leads to the formation of monolayer rings that further stack into nanotube assemblies (Figure 7, Cond. A). In pure MeOH, or at pH 1 or 11 in 10 % MeOH/H2O, porphyrin-driven nonspecific ag- gregation occurs (Figure 7, Cond. B). AFM and TEM images of the nanotubes confirmed the presence of nanorings, which stacked in a columnar fashion. The formation of a chiral assem- bly is revealed by the excitonic couplets due to both the naph- thalene diimide (NDI) and the porphyrin segments through NDI-NDI and porphyrin-porphy- rin interactions. In addition, the tendency of porphyrin conjugate 13 to form multilamellar nano- tubes is essentially driven by hy- drophobicity. Fluorescence and transient absorption spectrosco- py studies revealed that the nature of the assemblies has a tremendous influence on the electron-transfer/charge-recom- bination time constants. Time- correlated single-photon count- ing experiments in solution of MeOH with 580 nm excitation exhibited a triexponential decay, with lifetimes (tFl) of 1.96 ns (19%), 389 ps (63%), and 72 ps (18%). In a 10% MeOH/H2O so- lution, the low-intensity porphyrin-centered fluorescence emis- sion led to no detectable lifetime data. This could be attribut- ed to the slower charge separation in the 10 % MeOH/H2O so- lution ( 45-50 ps) than in pure MeOH, which leads to a signifi- cantly shorter-lived charge-separated state. Femtosecond tran- sient absorption experiments in MeOH showed the presence of NDI radical anion signals at 485 or 570-680 nm, however, the corresponding signals were missing in the MeOH/H2O mix- ture.

Another strategy adopted in assembling porphyrins is to use a host-guest strategy, and in this respect, cucurbit[n]urils occupy a central role.[27] Zhang et al. studied the self-organiza- tion of porphyrin 14, equipped with a naphthalene-methylpyr- idinium moiety (Figure 8a) and its co-assembly with cucurbi- t[7]uril (CB[7]) for preparing a supramolecular photosensitizer (Figure 8b).[28] The noncovalent assembly of 14/(CB[7])4 was found to be an effective genera- tor of 1O2 and thereby useful for the construction of supramolec- ular photosensitizers. As indicat- ed by the TEM images (Fig- ure 8c), molecule 14 self-assem- bles into spherelike aggregates. The absence of a clear contrast between the rim and the center of the spherical aggregates has shown that the aggregates are micellelike structures rather than hollow vesicles. The average hy- drodynamic diameter of the nanostructures, as determined by dynamic light scattering stud- ies, was found to be around 100 nm. The host-guest interac- tion between CB[7] and the naphthalene-methylpyridinium moiety of molecule 14 has been used as a tool to change the morphology from sphere to sheets (Figure 8d). The strong stacking tendency of hydropho- bic porphyrin chromophores using hydrophobic and p-p in- teractions is prevented by the hindering CB[7] molecules. The fluorescence intensity and the molar extinction coefficient of the porphyrin moiety increased upon addition of CB[7] to the aqueous solution of 14.

In a parallel investigation, Jiang and co-workers created a host-guest supramolecular polymer through assembly of a four-armed guest molecule, 5,10,15,20-tetrakis(N-carboxy- methyl-4-pyridinium)porphyrin tetrabromide (15) with tetramethylcucurbit[6]uril.[29] The strong host-guest interaction and hydrogen-bonding interactions be- tween the tetramethylcucurbit[6]uril molecules led to the for- mation of a two-dimensional supramolecular polymer network. A photocontrollable supramolecular hierarchical assembly has been created using orthogonal host-guest interaction of azo- benzene modified with water-soluble porphyrin 16 and differ- ent types of cyclodextrins.[30] The inclusion complex formed by azobenzene-porphyrin 16 with a permethyl b-cyclodextrin could be reversibly controlled by the addition of naphthyl- bridged bis(a-cyclodextrin). In addition, photoisomerization of the azobenzene moiety upon UV-light irradiation enabled re- versible control of the assembly and thereby resulted in a mor- phological transition from larger to smaller spheres.

An ionic solid is obtained when porphyrins have equal but opposite charges (see SnIV-tetrakis(4-sulfonatophenyl)porphyr- in 17 a and ZnII-tetrakis(N-ethanol-4-pyridinium)porphyrin 18 a).[31] These ionic solids exhibit microscale four-leaf-clover- shaped structures (Figure 9). The four combinations of the two metals in anionic (17 a and 17 b) and cationic (18 a and 18b) porphyrin have resulted in similar cloverlike structures with identical crystalline packing structures (Figure 9a-d). This clear- ly indicates that the intermolecular interactions due to the metals in the porphyrin play only a minor role and hence simi- lar cloverlike structures are obtained regardless of the metals within the porphyrin. The ionic strength of NaCl added to the solutions has a significant influence on the morphology of the clovers. Besides the ionic strength, the temperature was re- vealed to have a dramatic effect on the morphology. Upon in- creasing the temperature, the structures retain the basic four- fold symmetry of the clovers but with less-pronounced nano- scale features (Figure 9e-h). At 80 8C, the four-leaf-clover- shaped structure has been completely transformed into a smooth and podlike shape (Figure 9h). By varying the central metal ion, the porphyrin core can act either as an electron donor or electron acceptor. The photoconductive properties of the clovers obtained from the 1:1 assembly of the electron- donor ZnII-porphyrins and electron-acceptor SnIV-porphyrins have also been investigated by using conductive AFM. The clo- vers derived from the anionic ZnII-porphyrins and cationic SnIV-porphyrins exhibit strong photoconductivity. A fivefold in- crease in the current signal between the substrate and the tip was observed upon illumination conditions of the Zn/Sn clover. Notably, insulators were obtained when the metals of the two porphyrins were reversed.

A series of zwitterionic porphyrin diacids 19 a - c that self- and co-assembled to form J-type aggregates with distinct pho- tophysical properties and supramolecular nanostructures have also been reported.[32] Specifically, when molecules 19 a and 19 b are co-assembled, J-type aggregates with different types of binary excitonic bands have been obtained.[32b] The mixing of porphyrin 19 a and 19 b forms rod-shaped nanostructures, the height of which discontinuously changes upon varying the mixing ratio, and the length of which shortens with increasing percentage of 19 b until 50 %. In the mixed nanorods, non- or slightly overlapped bilayers correspond to those obtained for 19 a whereas the 19 b types are attributed to highly over- lapped bilayers. The occurrence of overlapping linear arrays of the porphyrins rather than the level of the monomers is the reason for the observed height difference in the co-assembly. The optical spectral features of the mixed J-aggregates indi- cate that the co-assembly is formed even at relatively low con- centrations and hence the products are formed under thermo- dynamic control rather than kinetic. The co-assembly involving 19 c and other porphyrins was different and always resulted in individual J-type aggregates.

Chiral supramolecular assemblies of porphyrins have been intensively explored to develop methodologies and protocols capable of transferring molecular chirality at the nano- and macroscopic level, by creating, for example, helical assemblie- s.[33a] As a strategy, the interaction of chiral metal complexes with 19 a resulted in the transfer of chirality from the metal complex to porphyrin J-aggregates.[31b] In another report, the handedness of the helical aggregates of trianionic porphyrin 20 could be controlled by rotational, gravitational, and orienta- tional forces.[34] The supramolecular chirality of the assembly is determined by both the chiral sign of the hydrodynamic flow and the magnetically tuned effective gravity. The application of these external forces at the nucleation step during the ag- gregation is found to be effective for chiral selection. Other ex- amples such as DNA,[35] peptides,[36] chiral templates,[37] surfac- tants,[38] and viruses[39] have also been used to organize por- phyrins.

Summary and Outlook The examples reported in this Minireview show once more how there is still "plenty of room" for the supramolecular ap- proach to engineer functional assemblies. The rational molecu- lar design and programming of appropriate interactions are the key components for creating functional materials. In this respect, a large series of architectures with unconventional structural morphologies composed of porphyrins have been prepared through the aid of various noncovalent polar interac- tions. In particular, the exploitation of columbic interactions and of the amphiphilic properties has been described to pre- pare functional morphologies in aqueous media. Some of the nanostructured materials displayed tunable and enhanced con- ductive properties, which are very attractive for engineering first devices.

Although prototypes of various functional devices have been proposed, the materials described in this study represent only a few examples of the efforts aimed at the design and preparation of porphyrin-based nanostructured materials that possess all the necessary characteristics for technological appli- cations. Owing to their ease in tuning electronic and structural properties, new porphyrin-based materials will continue to be developed, as more types of tetrapyrrolic macrocycles are manufactured to a high degree of performance for advanced energy applications such as photovoltaics or solar fuel cells. All of this will add a new degree of sophistication of materials based on the extraordinary as well as beautiful, flat tetrapyrrol- ic-based derivative.

Acknowledgements S.S.B. acknowledges the Marie Curie co-funding actions and the AUL for his Incoming Postdoctoral Fellowship. D.B. thanks the Eu- ropean Research Council (ERC) for supporting this research (COL- ORLANDS), the Science Policy Office of the Belgian Federal Gov- ernment (BELSPO-IAP 7/05 project), the EU through the FP7-NMP- 2012-SMALL-6 "SACS" project (contract no. GA-310651), the FRS- FNRS (FRFC contract no. 2.4.550.09), the "Loterie Nationale", the "TINTIN" ARC project (09/14-023), the MIUR through the FIRB "Futuro in Ricerca" ("SUPRACARBON'', contract no. RBFR10DAK6), and the University of Namur (internal funding).

After obtaining the ''Laurea'' from the University of Parma, and working with Enrico Dalcanale, Davide Bonifazi joined the group of Francois Diederich at the Swiss Federal Institute of Tech- nology, Zurich. After a one-year post- doctoral fellowship with Maurizio Prato at the University of Trieste, he joined the Department of Pharmaceut- ical Science at the same University. In September 2006, he joined the Depart- ment of Chemistry at the University of Namur, where he currently is a professor in organic chemistry. His research interests focus on the organic synthesis of electronically and optically active molecules and their self-assembly and self-or- ganization at interfaces, porphyrin chemistry, functionalization, and materials exploitation of carbon nanostructures.

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Received : March 4, 2014 Published online on June 12, 2014 Sukumaran Santhosh Babu[a] and Davide Bonifazi*[a, b] [a] Dr. S. S. Babu, Prof. D. Bonifazi Department of Chemistry and Namur Research College (NARC) University of Namur Rue de Bruxelles 61, 5000 Namur (Belgium) E-mail : [email protected] [b] Prof. D. Bonifazi Dipartimento di Scienze Chimiche e Farmaceutiche and UdR INSTM, Universit di Trieste Piazzale Europa 1, 34127 Trieste (Italy) (c) 2014 Blackwell Publishing Ltd.

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