Self-Assembly Monolayers (SAMs) are considered a promising route for solving technolog- ical hind... more Self-Assembly Monolayers (SAMs) are considered a promising route for solving technolog- ical hindrances (such as bias-stress, contact resistance, charge trapping) affecting the elec- trical performances of the Organic Field-Effect Transistors (OFETs). Here we use an OFET based on pentacene thin film to investigate the charge transport across conjugated SAMs at the Au/pentacene interface. We synthesized a homolog series of p-conjugated mole- cules, termed Tn-C8-SH, consisting of a n-unit oligothienyl Tn (n=1...4) bound to an octane-1-thiol (C8-SH) chain that self-assembles on the Au electrodes. The multi-paramet- ric response of such devices yields an exponential behavior of the field-effect mobility (l), current density (J), and total resistivity (R), due to the SAM at the charge injection interface (i.e. Au-SAM-pentacene). The surface treatment of the OFETs induces a clear stabilization of different parameters, like sub-threshold slope and threshold voltage, thanks to standard- ized steps in the fabrication process.
Azomethine liquid crystals (LCs), constituted by symmetric and asymmetric bithiophene or fluorene... more Azomethine liquid crystals (LCs), constituted by symmetric and asymmetric bithiophene or fluorene units as chromophores, were designed and synthesised. Their thermotropic behaviour was investigated using optical microscopy, differential scanning calorimetry, and wide angle X-ray diffraction. A lowering of transition temperatures was obtained by the introduction of the lateral methyl group as compared with unsubstituted compounds. The observed LC phases possess the classical textures of calamitic LCs. The optical properties of the target compounds were evaluated, both in solution and in solid state. A blue fluorescence was observed for fluorene containing compounds and a green fluorescence was observed for analogous bithiophene containing compounds. The introduction of a methyl lateral group onto the aromatic rings led to a remarkable increase in the solution emission properties.
The application of poly(p-xylylene)s as barrier and passivation layer is limited by the high tens... more The application of poly(p-xylylene)s as barrier and passivation layer is limited by the high tensile modulus of this class of materials. In this view, we propose a modified chemical vapor deposition approach to realize a series of copolymers based on parylene C, where linear alkyl chains partially replace the chlorides substituents. Thanks to the efficacious inclusion of bulky alkyl chains into the parylene layer, these modified materials show clear differences in both thermal and mechanical properties with respect to pristine parylene C. In particular, by following this approach, a decrease of the Young's modulus up to 0.3 GPa (13 times reduction of parylene C modulus) is observed, indicating a neat enhancement of the elastic behavior. Besides the improved mechanical performance, the modified materials retain both barrier and biocompatibility properties typical of neat parylene C. The results presented support copolymerization as a valuable approach for tuning parylene properties, which enlarges further the field of application of this excellent multipurpose material.
A detailed structural and orientational study on thin films of poly([n,n 0 -bis(2-octyldodecyl)-1... more A detailed structural and orientational study on thin films of poly([n,n 0 -bis(2-octyldodecyl)-11naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5 0 -(2,2 0 -12 bithiophene)) (P(NDI2OD-T2)) with low molecular weight is reported. The combination of grazing incidence diffraction with varied depth sensitivity and powder diffraction using synchrotron radiation provide new insights on the unit cell, confirming polymorphic behavior, and configuration ratio, i.e. face-versus edge-on. The effect of thermal treatment on microstructure is also presented. Insights of the macromolecule configuration, specifically the reciprocal position of bis-dicarboximide and bi-thiophene residues, are derived from simulation of 2D images based on reliable models.
The morphology and structure of the overlying poly(3-hexylthiophene) (P3HT) layer onto differentl... more The morphology and structure of the overlying poly(3-hexylthiophene) (P3HT) layer onto differently silanized silicon oxide has been studied by Atomic Force Microscopy (AFM) and X-Ray Diffraction (XRD) techniques. By increasing the silanizer alkyl chain length, the layer morphology evolves from a filament like to globular needle like as a consequence of the different SAM organization, while the P3HT conformation remains edge-on. For each case the effect of the annealing temperature has been studied. For all the cases a particular attention has been paid to the first thin layers close to the interface P3HT/SiOx. The effect of a polar substituent and presence of aromatic ring has been also studied.
Cycloolefin oligomers and polymers have attracted attention for functional materials, but they ar... more Cycloolefin oligomers and polymers have attracted attention for functional materials, but they are rarely seen in crystalline state. A new crystalline cycloolefin dicyclopentadiene tetramer, having a 2,3-exo-disyndiotactic structure, is presented. By combining global optimization techniques based on configurational sampling in generalized statistical ensembles, with very high quality synchrotron XRD data, the molecular mass of the crystallizing oligomer was first singled out, and its structure was then determined with a high degree of accuracy. The original procedures and methods developed for this particular case, can be considered a suitable reference to tackle the difficult characterization problems posed by the crystalline powders of organic materials in general.
Journal of Inorganic and Organometallic Polymers, 1996
The photochemistry of poly[bis(4-isopropylphenoxy)phosphazene] (PIPP) sensitized by hexakis(4-ben... more The photochemistry of poly[bis(4-isopropylphenoxy)phosphazene] (PIPP) sensitized by hexakis(4-benzoylphenoxy)cyclophosphazene and by poly[bis(4-benzoylphenoxy)phosphazene] was investigated both in solution and in film. Air-equilibrated CH2CI 2 solutions of this polymer, also containing the above-mentioned benzophenone-containing phosphazene substrates, were irradiated with light absorbed exclusively by the carbonyl substituent. The irradiation causes a sharp decrease of the viscosity, attributed to chain scission of the PIPP backbone. In this process the solvent plays a key role. On the other hand, no photochemical change was observed for the same pair of molecules in the solid state. X-ray diffraction studies and DSC investigations on PIPP films, doped with benzophenone-substituted cycloor poly-phosphazenes, reveal that the lack of photoreactivity is due to phase segregation in these systems.
The preparation and characterization of oligothienylene dialdehydes and related soluble copolymer... more The preparation and characterization of oligothienylene dialdehydes and related soluble copolymers in which thenylenic segments regularly alternate with phenylenic portions linked by azomethine moieties is presented. The polymer series with three, six and eight thienylenic residues showed interesting evidences of electronic confinement in low-gap segments (thienylenic). Self-assembled structures of oligomers can be obtained either by evaporation in high vacuum or by a proper thermal treatment of spin coated films, depending on the molecule length. Polymers prepared by different synthetic routes show different thermal and structural properties as a function of the ratio of two possible isomers at imino linkage. The order degree also influences the optical properties in fact luminescence data are strictly related to the percentage of the two isomers. 0 1998 Elsevier Science B.V.
An exemplary system suitable for optoelectronics applications, i.e. poly(3-hexylthiophene), herei... more An exemplary system suitable for optoelectronics applications, i.e. poly(3-hexylthiophene), hereinafter P3HT, deposited by spin casting onto silicon substrates functionalised by three selected molecules and then properly annealed, has been examined. Grazing Incidence X-ray Scattering (GIXS) measurements have been performed with 4-circle diffractometer, allowing for a fine control of sample axes movement.
The deposition of thin ®lms of 3,3 HH ,4 HHH ,3 HHHHH -tetrahexyl-2,2 H :5 H ,2 HH :5 HH ,2 HHH :... more The deposition of thin ®lms of 3,3 HH ,4 HHH ,3 HHHHH -tetrahexyl-2,2 H :5 H ,2 HH :5 HH ,2 HHH :5 HHH ,2 HHHH :5 HHHH ,2 HHHHH -sexithiophene (4H6T) has been performed in ultra-high vacuum conditions by using organic molecular beam deposition (OMBD). Once temperature and pressure are optimized, the substrate choice is the key factor in determining the properties of the deposited ®lms. From the structural analysis of samples deposited on dierent inorganic and organic substrates as well as from the comparison with crystalline polymorphs of 4H6T, useful information for the control of both structural order and molecular orientation in the ®lms are inferred. The results of structural investigations by X-ray diraction, compared with optical analyses (electronic absorption and photoluminescence), are indicative of either intermolecular or sub-strate±4H6T interactions. Ó
We report on the intercalation of a cationic fluorescent oligo(fluorene) in between the 2D interl... more We report on the intercalation of a cationic fluorescent oligo(fluorene) in between the 2D interlayer region of a fluoromica type silicate. The formation of intercalated structures with different fluorophore contents is observed in powders by synchrotron radiation XRD. Successively, the hybrids are dispersed in poly(styrene) through in situ polymerization. Such a procedure allows us to synthesize the materials from solution, to achieve solid films, and to characterize them by optical and morphologic techniques. The polymeric films with homogeneous distribution of the hybrids exhibit ultraviolet-blue photoluminescence with a significantly enhanced photostability compared to the bare oligo(fluorene)s. Finally, under specific conditions, the polymer hybrid with higher oligo(fluorene) content spontaneously assembles into highly ordered microporous films.
ABSTRACT Molecular beam deposition of quaterthiophene oligomer on a single crystal of potassium a... more ABSTRACT Molecular beam deposition of quaterthiophene oligomer on a single crystal of potassium acid phtalate yields thin films exhibiting a novel supramolecular organisation which has been determined by a combined study of X-ray diffraction and polarized optical transmission measurements. In this structure consisting of stacks of tilted H aggregates, a commensurate ratio between the KAP substrate and the overgrown oligothiophene layer (quasi-epitaxial growth) is attained. The samples are optically extremely anisotropic, with the projection of the molecular axis on the substrate surface perfectly aligned along the b crystallographic axis. Using these novel structural data, the optical properties are interpreted within the framework of the transition density approach.
Self-Assembly Monolayers (SAMs) are considered a promising route for solving technolog- ical hind... more Self-Assembly Monolayers (SAMs) are considered a promising route for solving technolog- ical hindrances (such as bias-stress, contact resistance, charge trapping) affecting the elec- trical performances of the Organic Field-Effect Transistors (OFETs). Here we use an OFET based on pentacene thin film to investigate the charge transport across conjugated SAMs at the Au/pentacene interface. We synthesized a homolog series of p-conjugated mole- cules, termed Tn-C8-SH, consisting of a n-unit oligothienyl Tn (n=1...4) bound to an octane-1-thiol (C8-SH) chain that self-assembles on the Au electrodes. The multi-paramet- ric response of such devices yields an exponential behavior of the field-effect mobility (l), current density (J), and total resistivity (R), due to the SAM at the charge injection interface (i.e. Au-SAM-pentacene). The surface treatment of the OFETs induces a clear stabilization of different parameters, like sub-threshold slope and threshold voltage, thanks to standard- ized steps in the fabrication process.
Azomethine liquid crystals (LCs), constituted by symmetric and asymmetric bithiophene or fluorene... more Azomethine liquid crystals (LCs), constituted by symmetric and asymmetric bithiophene or fluorene units as chromophores, were designed and synthesised. Their thermotropic behaviour was investigated using optical microscopy, differential scanning calorimetry, and wide angle X-ray diffraction. A lowering of transition temperatures was obtained by the introduction of the lateral methyl group as compared with unsubstituted compounds. The observed LC phases possess the classical textures of calamitic LCs. The optical properties of the target compounds were evaluated, both in solution and in solid state. A blue fluorescence was observed for fluorene containing compounds and a green fluorescence was observed for analogous bithiophene containing compounds. The introduction of a methyl lateral group onto the aromatic rings led to a remarkable increase in the solution emission properties.
The application of poly(p-xylylene)s as barrier and passivation layer is limited by the high tens... more The application of poly(p-xylylene)s as barrier and passivation layer is limited by the high tensile modulus of this class of materials. In this view, we propose a modified chemical vapor deposition approach to realize a series of copolymers based on parylene C, where linear alkyl chains partially replace the chlorides substituents. Thanks to the efficacious inclusion of bulky alkyl chains into the parylene layer, these modified materials show clear differences in both thermal and mechanical properties with respect to pristine parylene C. In particular, by following this approach, a decrease of the Young's modulus up to 0.3 GPa (13 times reduction of parylene C modulus) is observed, indicating a neat enhancement of the elastic behavior. Besides the improved mechanical performance, the modified materials retain both barrier and biocompatibility properties typical of neat parylene C. The results presented support copolymerization as a valuable approach for tuning parylene properties, which enlarges further the field of application of this excellent multipurpose material.
A detailed structural and orientational study on thin films of poly([n,n 0 -bis(2-octyldodecyl)-1... more A detailed structural and orientational study on thin films of poly([n,n 0 -bis(2-octyldodecyl)-11naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5 0 -(2,2 0 -12 bithiophene)) (P(NDI2OD-T2)) with low molecular weight is reported. The combination of grazing incidence diffraction with varied depth sensitivity and powder diffraction using synchrotron radiation provide new insights on the unit cell, confirming polymorphic behavior, and configuration ratio, i.e. face-versus edge-on. The effect of thermal treatment on microstructure is also presented. Insights of the macromolecule configuration, specifically the reciprocal position of bis-dicarboximide and bi-thiophene residues, are derived from simulation of 2D images based on reliable models.
The morphology and structure of the overlying poly(3-hexylthiophene) (P3HT) layer onto differentl... more The morphology and structure of the overlying poly(3-hexylthiophene) (P3HT) layer onto differently silanized silicon oxide has been studied by Atomic Force Microscopy (AFM) and X-Ray Diffraction (XRD) techniques. By increasing the silanizer alkyl chain length, the layer morphology evolves from a filament like to globular needle like as a consequence of the different SAM organization, while the P3HT conformation remains edge-on. For each case the effect of the annealing temperature has been studied. For all the cases a particular attention has been paid to the first thin layers close to the interface P3HT/SiOx. The effect of a polar substituent and presence of aromatic ring has been also studied.
Cycloolefin oligomers and polymers have attracted attention for functional materials, but they ar... more Cycloolefin oligomers and polymers have attracted attention for functional materials, but they are rarely seen in crystalline state. A new crystalline cycloolefin dicyclopentadiene tetramer, having a 2,3-exo-disyndiotactic structure, is presented. By combining global optimization techniques based on configurational sampling in generalized statistical ensembles, with very high quality synchrotron XRD data, the molecular mass of the crystallizing oligomer was first singled out, and its structure was then determined with a high degree of accuracy. The original procedures and methods developed for this particular case, can be considered a suitable reference to tackle the difficult characterization problems posed by the crystalline powders of organic materials in general.
Journal of Inorganic and Organometallic Polymers, 1996
The photochemistry of poly[bis(4-isopropylphenoxy)phosphazene] (PIPP) sensitized by hexakis(4-ben... more The photochemistry of poly[bis(4-isopropylphenoxy)phosphazene] (PIPP) sensitized by hexakis(4-benzoylphenoxy)cyclophosphazene and by poly[bis(4-benzoylphenoxy)phosphazene] was investigated both in solution and in film. Air-equilibrated CH2CI 2 solutions of this polymer, also containing the above-mentioned benzophenone-containing phosphazene substrates, were irradiated with light absorbed exclusively by the carbonyl substituent. The irradiation causes a sharp decrease of the viscosity, attributed to chain scission of the PIPP backbone. In this process the solvent plays a key role. On the other hand, no photochemical change was observed for the same pair of molecules in the solid state. X-ray diffraction studies and DSC investigations on PIPP films, doped with benzophenone-substituted cycloor poly-phosphazenes, reveal that the lack of photoreactivity is due to phase segregation in these systems.
The preparation and characterization of oligothienylene dialdehydes and related soluble copolymer... more The preparation and characterization of oligothienylene dialdehydes and related soluble copolymers in which thenylenic segments regularly alternate with phenylenic portions linked by azomethine moieties is presented. The polymer series with three, six and eight thienylenic residues showed interesting evidences of electronic confinement in low-gap segments (thienylenic). Self-assembled structures of oligomers can be obtained either by evaporation in high vacuum or by a proper thermal treatment of spin coated films, depending on the molecule length. Polymers prepared by different synthetic routes show different thermal and structural properties as a function of the ratio of two possible isomers at imino linkage. The order degree also influences the optical properties in fact luminescence data are strictly related to the percentage of the two isomers. 0 1998 Elsevier Science B.V.
An exemplary system suitable for optoelectronics applications, i.e. poly(3-hexylthiophene), herei... more An exemplary system suitable for optoelectronics applications, i.e. poly(3-hexylthiophene), hereinafter P3HT, deposited by spin casting onto silicon substrates functionalised by three selected molecules and then properly annealed, has been examined. Grazing Incidence X-ray Scattering (GIXS) measurements have been performed with 4-circle diffractometer, allowing for a fine control of sample axes movement.
The deposition of thin ®lms of 3,3 HH ,4 HHH ,3 HHHHH -tetrahexyl-2,2 H :5 H ,2 HH :5 HH ,2 HHH :... more The deposition of thin ®lms of 3,3 HH ,4 HHH ,3 HHHHH -tetrahexyl-2,2 H :5 H ,2 HH :5 HH ,2 HHH :5 HHH ,2 HHHH :5 HHHH ,2 HHHHH -sexithiophene (4H6T) has been performed in ultra-high vacuum conditions by using organic molecular beam deposition (OMBD). Once temperature and pressure are optimized, the substrate choice is the key factor in determining the properties of the deposited ®lms. From the structural analysis of samples deposited on dierent inorganic and organic substrates as well as from the comparison with crystalline polymorphs of 4H6T, useful information for the control of both structural order and molecular orientation in the ®lms are inferred. The results of structural investigations by X-ray diraction, compared with optical analyses (electronic absorption and photoluminescence), are indicative of either intermolecular or sub-strate±4H6T interactions. Ó
We report on the intercalation of a cationic fluorescent oligo(fluorene) in between the 2D interl... more We report on the intercalation of a cationic fluorescent oligo(fluorene) in between the 2D interlayer region of a fluoromica type silicate. The formation of intercalated structures with different fluorophore contents is observed in powders by synchrotron radiation XRD. Successively, the hybrids are dispersed in poly(styrene) through in situ polymerization. Such a procedure allows us to synthesize the materials from solution, to achieve solid films, and to characterize them by optical and morphologic techniques. The polymeric films with homogeneous distribution of the hybrids exhibit ultraviolet-blue photoluminescence with a significantly enhanced photostability compared to the bare oligo(fluorene)s. Finally, under specific conditions, the polymer hybrid with higher oligo(fluorene) content spontaneously assembles into highly ordered microporous films.
ABSTRACT Molecular beam deposition of quaterthiophene oligomer on a single crystal of potassium a... more ABSTRACT Molecular beam deposition of quaterthiophene oligomer on a single crystal of potassium acid phtalate yields thin films exhibiting a novel supramolecular organisation which has been determined by a combined study of X-ray diffraction and polarized optical transmission measurements. In this structure consisting of stacks of tilted H aggregates, a commensurate ratio between the KAP substrate and the overgrown oligothiophene layer (quasi-epitaxial growth) is attained. The samples are optically extremely anisotropic, with the projection of the molecular axis on the substrate surface perfectly aligned along the b crystallographic axis. Using these novel structural data, the optical properties are interpreted within the framework of the transition density approach.
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Papers by William Porzio