Effect of peripheral hydrophobic alkoxy substitution on the organic field effect transistor performance of amphiphilic tris(phthalocyaninato) europium triple-decker complexes

A series of four amphiphilic heteroleptic tris(phthalocyaninato) europium complexes with different lengths of hydrophobic alkoxy substituents on one outer phthalocyanine ligand [Pc(15C5)4]Eu[Pc(15C5)4]Eu[Pc(OCnH(2n+1))8] (n = 4, 6, 10,12) (1, 2, 4, and 5) was designed and prepared. Their film forming and organic field effect transistor properties have been systematically studied in comparison with analogous [Pc(15C5)4]Eu[Pc(15C5)4]Eu[Pc(OC8H17)8] (3). Experimental results showed that all these typical amphiphilic sandwich triple-decker molecules have been fabricated into highly ordered films by the Langmuir-Blodgett (LB) technique, which displays carrier mobility in the direction parallel to the aromatic phthalocyanine rings in the range of 0.0032-0.60 cm2 V(-1) s(-1) depending on the length of the hydrophobic alkoxy substituents. This is rationalized on the basis of comparative morphology analysis results of the LB films by the atomic force microscopy technique.     

Thin-film transistors based on Langmuir-Blodgett films of heteroleptic bis(phthalocyaninato) rare earth complexes

An ordered molecular assembly of heteroleptic bis(phthalocyaninato) rare earth complexes M(Pc)[Pc(OC8H17)8] [M = Tb, Lu; H2Pc = phthalocyanine; H2Pc(OC8H17)8 = 2,3,9,10,16,17,23,24-octakis(octyloxy)phthalocyanine] has been fabricated by the Langmuir-Blodgett (LB) technique and characterized by surface pressure-area isotherms, electronic absorption and polarized electronic absorption spectroscopy, low-angle X-ray diffraction, and atomic force microscopy. The molecular ordering in the LB multilayer film on SiO2 substrate was made into a p-channel field effect transistor (FET), which was generally operated in the enhanced mode. The energy levels of the highest occupied molecular orbital and the lowest unoccupied molecular orbital as well as the energy band diagram can be deduced from the electrochemical measurement results. The charge mobilities of Tb(Pc)[Pc(OC8H17)8] and Lu(Pc)[Pc(OC8H17)8] were calculated to be about 6.4 x 10(-4) and 1.7 x 10(-3) cm2 V(-1) s(-1), respectively.     

Arrangement of tris(phthalocyaninato) gadolinium triple-decker complexes with multi-octyloxy groups on water surface

A series of five carefully designed tris(phthalocyaninato) gadolinium triple-decker complexes [Pc(R)8]Gd[Pc(R')8]Gd[Pc(R')8] (R=R'=R'=H; R=R'=H, R'=OC8H17; R=R'=H, R'=OC8H17; R=H, R'=R'=OC8H17; R=R'=R'=OC8H17) (1-5) were prepared and the film forming properties on water surface were systematically investigated. The limited mean molecular area obtained by pi-A isotherms revealed an "edge-on" conformation for all these compounds. UV-vis absorption spectra showed red-shifted Q bands, indicating the formation of J aggregates and effective intermolecular interaction in solid film. Phthalocyanine rings were found to take tilted orientation with respect to the normal of substrate according to the polarized absorption spectroscopic measurements. Low angle X-ray diffraction results provide direct evidence and therefore clearly clarify the point, for the first time, that unsymmetrical triple-decker molecules pack on the water surface with the unsubstituted phthalocyanine ring set close to the water surface and the substituted phthalocyanine ligand with octyloxy groups lies on the top.     

Ferrocene-decorated (phthalocyaninato)(porphyrinato) double- and triple-decker rare earth complexes: synthesis, structure, and electrochemical properties

A series of four mixed (phthalocyaninato)(porphyrinato) rare earth double-decker complexes (Pc)M[Por(Fc)(2)] [Pc = phthalocyaninate; Por(Fc)(2) = 5,15-di(ferrocenyl)-porphyrinate; M = Eu (1), Y (2), Ho (3), Lu (4)] and their europium(III) triple-decker counterpart (Pc)Eu(Pc)Eu[Por(Fc)(2)] (5), each with two ferrocenyl units at the meso-positions of their porphyrin ligands, have been designed and prepared. The double- and triple-decker complexes 1-5 were characterized by elemental analysis and various spectroscopic methods. The molecular structures of two double-deckers 1 and 4 were also determined by single-crystal X-ray diffraction analysis. Electrochemical studies of these novel sandwich complexes revealed two consecutive ferrocene-based one-electron oxidation waves, suggesting the effective electronic coupling between the two ferrocenyl units. Nevertheless, the separation between the two consecutive ferrocene-based oxidation waves increases from 1 to 4, along with the decrease of rare earth ionic radius, indicating the effect of rare earth size on tuning the coupling between the two ferrocenyl units. Furthermore, the splitting between the two ferrocene-based one-electron oxidations for triple-decker 5 is even smaller than that for 1, showing that the electronic interaction between the two ferrocene centers can also be tuned through changing the linking sandwich framework from double-decker to triple-decker. For further understanding of the electronic coupling between ferrocenyl groups, DFT calculation is carried out to clarify the electronic delocalization and the molecular orbital distribution in these double-decker complexes.     

High performance n-type organic field-effect transistors based on pi-electronic systems with trifluoromethylphenyl groups

Novel pi-electron systems with trifluoromethylphenyl groups and/or a thiazolothiazole unit were developed as n-type semiconductors for OFETs. They showed excellent n-type performances with high electron mobilities. The trifluoromethylphenyl group was found to be very effective in inducing n-type behavior. The thiazolothiazole unit was favorable for forming stacking structures leading to efficient intermolecular pi-pi interactions.     

Optically active mixed (phthalocyaninato)(porphyrinato) rare earth triple-decker complexes. Synthesis, spectroscopy, and effective chiral information transfer

With the view to creating novel sandwich-type tetrapyrrole rare earth complexes toward potential applications in material science and chiral catalysis, two new optically active mixed (phthalocyaninato)(porphyrinato) rare earth triple-decker complexes with both (R)- and (S)-enantiomers [M(2)(Pc)(2)(TCBP)] {TCBP = Meso-tetrakis [3,4-(11,12:13,14-di(1',2'-naphtho)-1,4,7,10,15,18-hexaoxacycloeicosa-2,11,13-triene)-phenyl] porphyrinate; M = Eu (1), Y (2)} have been designed and prepared by treating optically active metal free porphyrin (R)-/(S)-H(2)TCBP with M(Pc)(2) in the presence of corresponding M(acac)(3)·nH(2)O (acac = acetylacetonate) in refluxing 1,2,4-trichlorobenzene (TCB). These novel mixed ring rare earth triple-decker compounds were characterized by a wide range of spectroscopic methods including MS, (1)H NMR, IR, electronic absorption, and magnetic circular-dichroism (MCD) spectroscopic measurements in addition to elemental analysis. Perfect mirror image relationship was observed in the Soret and Q absorption regions in the circular-dichroism (CD) spectra of the (R)- and (S)-enantiomers, indicating the optically active nature of these two mixed (phthalocyaninato)(porphyrinato) rare earth triple-decker complexes. This result reveals the effective chiral information transfer from the peripheral chiral binaphthyl units to the porphyrin and phthalocyanine chromophores in the triple-decker molecule because of the intense π-π interaction between porphyrin and phthalocyanine rings. In addition, their electrochemical properties have also been investigated by cyclic voltammetry (CV).     

High performance n- and p-type field-effect transistors based on tetrathiafulvalene derivatives

The first n-type FET based on TTF derivatives was prepared. TTF derivatives with halogeno-substituted quinoxaline rings showed excellent n- or p-type performances with high carrier mobilities. Introduction of halogen groups determined the FET polarity by controlling the HOMO and LUMO levels of the molecules. The pi-stacking structures were observed in the single crystals of tetrahalogeno-TTFs.     

High-performance organic field-effect transistors based on pi-extended tetrathiafulvalene derivatives

Aromatic ring-condensed TTF derivatives exhibited excellent p-type FET performances in thin films. Introduction of fused benzene and pyrazine rings to the TTF skeleton was effective to enhance the intermolecular interactions and stability to oxygen. Ordered molecular alignment was confirmed by XRD studies. A pi-stacking structure was observed in the single crystal of diquinoxalinoTTF.     

Synthesis, characterization, and OFET properties of amphiphilic heteroleptic tris(phthalocyaninato) europium(III) complexes with hydrophilic poly(oxyethylene) substituents

A series of amphiphilic heteroleptic tris(phthalocyaninato) europium complexes with hydrophilic poly(oxyethylene) heads and hydrophobic alkoxy tails {Pc[(OC2H4)2OCH3]8}Eu{Pc[(OC2H4)2OCH3]8}Eu[Pc(OCnH2n + 1)8] (n = 6, 8, 10,12) (1-4) were designed and prepared from the reaction between homoleptic bis(phthalocyaninato) europium compound {Pc[(OC2H4)2OCH3]8}Eu{Pc[(OC2H4)2OCH3]8} and metal-free 2,3,9,10,16,17,23,24-octakis(alkoxy)phthalocyanine H2Pc(OCnH2n + 1)8 (n = 6, 8, 10,12) in the presence of Eu(acac)3.H2O (Hacac = acetylacetone) in boiling 1,2,4-trichlorobenzene (TCB). These novel sandwich triple-decker complexes have been characterized by a wide range of spectroscopic methods and have been electrochemically studied. With the help of the Langmuir-Blodgett (LB) technique, these typical amphiphilic triple-decker complexes have been fabricated into organic field effect transistors (OFET) with an unusual bottom contact configuration. The devices display good OFET performance with the carrier mobility for holes in the direction parallel to the aromatic phthalocyanine rings, which shows dependence on the length of the hydrophobic alkoxy side chains, decreasing from 0.46 for 1 to 0.014 cm2 V(-1) s(-1) for 4 along with the increase in the carbon number in the hydrophobic alkoxy side chains.     

A novel efficient approach to heteronuclear triple-decker complexes of rare earth elements with phthalocyanines

A novel approach to heteroleptic heteronuclear rare earth metal(III) trisphthalocyaninates was proposed with the complexes [(15C5)₄Pc]M*[(15C5)₄Pc]M(Pc) as examples (15C5 is 15-crown-5, Pc^2? is the phthalocyaninate dianion, and M* ?? M = Yb and Y). Unsubstituted lanthanum bisphthalocyaninate, La(Pc)₂, was used for the first time as a Pc^2? donor in the synthesis of such complexes. This substantially increased the yields of the target heteronuclear complexes over the previous literature data.     

Infrared spectra of phthalocyanine and naphthalocyanine in sandwich-type (na)phthalocyaninato and porphyrinato rare earth complexes. Part 3. The effects of substituents and molecular symmetry on the infrared characteristics of phthalocyanine in bis(phthalocyaninato) rare earth complexes

The infra-red (IR) spectroscopic data for a series of 45 homoleptic unsubstituted and substituted bis(phthalocyaninato) rare earth complexes M(Pc)2 and M(Pc*)2 [M=Y, La...Lu except Pm; H2Pc=phthalocyanine; H2Pc*=2,3,9,10,16,17,24,25-octakis(octyloxy)phthalocyanine (H2OOPc) and 2(3),9(10),16(17),24(25)-tetra(tert-butyl)phthalocyanine (H2TBPc)] have been collected with resolution of 2 cm(-1). The IR spectra for M(Pc)2 and M(OOPc)2 are much simpler than those of M(TBPc)2, revealing the relatively higher symmetry of the former two compounds. For M(Pc)2 the Pc-* marker band at 1312-1323 cm(-1), attributed to the pyrrole stretching, and the isoindole stretching band at 1439-1454 cm(-1) are found to be dependent on the central rare earth size, shifting slightly to the higher energy along with the decrease of rare earth radius. The frequency of the vibration at 876-887 cm(-1) is also dependent on the rare earth ionic size. The metal size-sensitivity of this band and theoretical studies render it possible to re-assign it to the coupling of isoindole deformation and aza vibration. The nature of another metal-sensitive vibration mode at 1110-1116 cm(-1), which was previously assigned to the C-H bending, is now re-assigned as an isoindole breathing mode with some small contribution also from C-H in-plane bending. These assignments are supported by comparative studies of the IR spectra of substituted bis(phthalocyaninato) analogues M(OOPc)2 and M(TBPc)2. By comparison between the IR spectra of unsubstituted and substituted bis(phthalocyaninato) rare earth analogues and according to the IR characteristics of alkyl groups, some characteristic vibrational fundamentals due to the Pc rings and the substituents can be separately identified. In conclusion, all the metal size-dependent IR absorptions are composed primarily of the vibrations of pyrrole or isoindole stretching, breathing or deformation or aza stretching of the Pc ring.     

Synthesis,spectroscopic characterisation and structure of the first chiral heteroleptic bis(phthalocyaninato) rare earth complexes

Treatment of MIII(Pc)(acac) (M = Sm, Eu, Gd; Pc = phthalocyaninate; acac = acetylacetonate), generated in situ, with 3-(3-pentyloxy)phthalonitrile in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in n-pentanol affords racemic mixtures of the chiral double-deckers MIII(Pc)[Pc(OC5H11)4] [Pc(OC5H11)4 = 1,8,15,22-tetrakis(3-pentyloxy)phthalocyaninate], which have been spectroscopically and structurally characterised.     

Infrared spectroscopic characteristics of octa-substituted bis(phthalocyaninato) rare earth complexes peripherally substituted with (4-methoxy)phenoxy derivatives

The infrared (IR) spectroscopic data for a series of 15 rare earth double-deckers M[Pc(MeOPhO)(8)](2) [M=Y, La, ..., Lu, except Pm; H(2)Pc=2, 3, 9, 10, 16, 17, 23, 24-octakis(4-methoxyphenoxy)phthalocyanine] with tervalent rare earths M(III)[Pc(MeOPhO)(8)](2) (M=Y, La, ..., Lu except Ce and Pm) and intermediate-valent cerium Ce[Pc(MeOPhO)(8)](2) have been collected with resolution of 2cm(-1). For M(III)[Pc(MeOPhO)(8)](2), typical IR marker band of the monoradical anion Pc(MeOPhO)(8)(-) shows characteristic absorption band whose frequency linearly varies in the range from 1,313 cm(-1) as a weak band for La[Pc(MeOPhO)(8)](2) to 1,324 cm(-1) as a medium band for Lu[Pc(MeOPhO)(8)](2) along with the decrease of rare earth ionic size. For Ce[Pc(MeOPhO)(8)](2), a weak band at 1,324 cm(-1) with contribution from pyrrole stretching was the marker IR band of phthalocyanine dianion Pc(2-). In conclusion, all the metal size-dependent IR absorptions should be contributed primarily from the vibrations of pyrrole, isoindole stretching, breathing or deformation or aza stretching of the Pc ring.     

Raman spectroscopic characteristics of octa-substituted bis(phthalocyaninato) rare earth complexes peripherally substituted with (4-methoxy)phenoxy derivatives

The Raman spectroscopic data in the range 500-1800 cm⁻¹ for a series of 15 rare earth double-deckers with tervalent rare earths M^III[Pc(MeOPhO)₈]₂ (M = Y, La, …, Lu, except Ce, Pr and Pm), reduced state HPr[Pc(MeOPhO)₈]₂ and intermediate-valent cerium Ce[Pc(MeOPhO)₈]₂ have been collected using laser excitation source emitting at 632.8 nm. With excitation at 632.8 nm, which is in close resonance with the main Q absorption band of the phthalocyanine ligand, typical Raman marker bands of the monoanion radical [Pc(MeOPhO)₈]⁻ were observed at 1500-1528 cm⁻¹ as very strong bands resulting from the coupling of pyrrole CC and aza CN stretchings. For Ce[Pc(MeOPhO)₈]₂ and HPr[Pc(MeOPhO)₈]₂, a very strong band at 1499 cm⁻¹ with contributions from both pyrrole CC and aza CN stretchings and also isoindole stretching was the marker Raman band of [Pc(MeOPhO)₈]²⁻. In addition, the influence of ionic radius of the rare earth metal and substituent species on the Raman scatting characteristics of sandwich-type compounds has also been tentatively studied.     

Vibrational spectroscopy of phthalocyanine and naphthalocyanine in sandwich-type (na)phthalocyaninato and porphyrinato rare earth complexes. Part 15: The IR characteristics of phthalocyanine in homoleptic tetrakis(phthalocyaninato) rare earth(III)-cadmium(II) quadruple-deckers

The infra-red (IR) spectroscopic data for a series of twelve sandwich-type homoleptic tetrakis[2,3,9,10,16,17,23,24-octa(octyloxy)phthalocyaninato] rare earth(III)-cadmium(II) quadruple-decker complexes [Pc(OC₈H₁₇)₈]M[Pc(OC₈H₁₇)₈]Cd[Pc(OC₈H₁₇)₈]M[Pc(OC₈H₁₇)₈] (M = Y, Pr–Yb except Pm) have been collected with resolution of 2 cm⁻¹ and their interpretation in terms tried by analogy with the IR characteristics of bis(phthalocyaninato) cerium double-decker [Pc(OC₈H₁₇)₈]Ce[Pc(OC₈H₁₇)₈] in which the macrocyclic ligands exist as the phthalocyanine dianion. Similar to the bis/tris(phthalocyaninato) rare earth sandwich counterparts, all the absorptions contributed primarily by or at least containing contribution from the vibrations of pyrrole or isoindole stretching, breathing or deformation or aza stretching in the IR spectra of these quadruple-decker compounds show dependent nature on the rare earth ionic size. The shift toward higher energy direction in the frequencies of these vibrations along with the decrease of the rare earth radii reveals the effective and increasing π–π interactions in these quadruple-decker sandwich compounds in the same order. Nevertheless, the decreased sensitivity of the frequencies of the above mentioned vibration modes in particular the weak absorption band due to the isoindole stretching at 1414–1416 cm⁻¹ for the quadruple-decker on rare earth metal size in comparison with corresponding band for bis(phthalocyaninato) rare earth counterparts indicates the relatively weaker π–π interaction in these quadruple-deckers than in the double-deckers.     

Highly responsive biosensors based on organic field-effect transistors under light irradiation

High responsivity and sensitivity play essential roles in the development of organic field-effect transistors (OFETs)-based biosensors with regard to biological detections, particularly for disease diagnosis. Nonetheless, how to design a biosensor which improves these two outstanding properties while achieving low cost, easy processing, and time saving is a daunting challenge. Herein, a novel biosensor based on OFET with copolymer thin film, whose surface is illuminated with a suitable light beam is reported. This film can be used as both an organic semiconductor material and as a photoelectric active material. Due to amplification of signals as a result of the film’s strong response to light, the biosensor possesses higher responsivity and sensitivity compared to dark condition and even realizes a maximum responsivity of up to 10³ for alpha-fetoprotein (AFP) detection. The simple combination of light and transistor builds a bridge between photoelectric effect and biological system. In addition, the emergence of more excellent photoelectric active materials is expected to pave a way for ultrasensitive bio-chemical diagnostic tools.     

Infra-red and Raman spectroscopic study of tetra-substituted bis(phthalocyaninato) rare earth complexes peripherally substituted with tert-butyl derivatives

The infra-red spectroscopic data for a series of 13 homoleptic substituted bis(phthalocyaninato) rare earth complexes with tervalent rare earths M(III)(TBPc)(2) [M=Y, Pr, ..., Lu except La, Ce and Pm; TBPc=dianion of 3(4),12(13),21(22),30(31)-tetra(tert-butyl)-phthalocyanine] have been collected with resolution of 2 cm(-1). Raman spectroscopic properties in the range of 500-1,800 cm(-1) for these double-deckers M(III)(TBPc)(2) have been collected using laser excitation sources emitting at 632.8 nm. Both the IR and Raman spectra for M(III)(TBPc)(2) are more complicated than those of homoleptic bis(phthalocyaninato) rare earth analogues due to the decreased molecular symmetry of these double-decker compounds. For this series, the IR typical marker band of (TBPc)(-) appears as an intense absorption at 1,314-1,319 cm(-1), attributed to the pyrrole stretching. Under excitation at 632.8 nm that is in close resonance with the main Q absorption band of phthalocyanine ligand, typical Raman marker band of the monoanion radical (TBPc)(-) was observed at 1,515-1,530 cm(-1) resulting from aza CN stretching. Both techniques reveal that the frequencies of pyrrole stretching, isoindole breathing and aza stretchings depend on the rare earth ionic size, shifting to higher energy along with the lanthanide contraction due to the increased ring-ring interaction across the series.     

Enhanced performance of field-effect transistors based on C_(60) single crystals with conjugated polyelectrolyte

Contact resistance at the interface between metal electrodes and semiconductors can significantly limit the performance of organic field-effect transistors,leading to a distinct voltage drop at the interface.Here,we demonstrate enhanced performance of n-channel field-effect transistors based on solution-grown C_(60) single-crystalline ribbons by introducing an interlayer of a conjugated polyelectrolyte(CPE) composed of poly[(9,9-bis(3'-((N,N-dimethyl)-N-ethylamnionium)-propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)]dibromide(PFN~+Br~-).The PFN~+Br~-interlayer greatly improves the charge injection.Consequently,the electron mobility is promoted up to 5.60 cm~2V~(-1) s~(-1) and the threshold voltage decreased dramatically with the minimum of4.90 V.     

The effects of substituents,molecular symmetry,ionic radius of the rare earth metal,and macrocycle on the electronic absorption spectra characteristics of sandwich-type bis(phthalocyaninato) and mixed (phthalocyaninato)(porphyrinato) rare earth complexes

The electronic absorption spectroscopic data for two series of 60 unsubstituted/substituted bis(phthalocyaninato) and mixed [tetrakis(4-chlorophenyl)porphyrinato](phthalocyaninato) rare earth complexes M(Pc)₂, M(Pc^∗)₂ and M(TClPP)(Pc) [M = Y, La…Lu except Pm; Pc^∗ = dianion of 2,3,9,10,16,17,23,24-octakis(4-methoxyphenoxy)phthalocyanine [Pc(MeOPhO)₈], dianion of 3(4),12(13),21(22),30(31)-tetra(tert-butyl)phthalocyanine (TBPc) and TClPP = tetra(4-chloro)phenylporphyrin] have been measured in CHCl₃. In this paper, the influence of the symmetry of macrocycle rare earth molecules, the effects of ionic radius of the rare earth metal and the influence of substituent species (tert-butyl and 4-methoxyphenoxy groups) onto the peripheral benzene rings on the electronic absorption characteristics of sandwich-type compounds have also been tentatively studied in detail.