Extensibility effect of poly(3-hexylthiophene) on the glucose sensing performance of mixed poly(3-hexylthiophene)/octadecylamine/glucose oxidase Langmuir-Blodgett films

EQCM Analysis of the Insertion Phenomena in a n-Doped Poly-Alkyl-Terthiophene With Regioregular Pattern of Substitution

In the present work, we have undertaken the study of the n-doping process in poly-3,3″-didodecyl-2,2':5',2″-terthiophene (poly-33″-DDTT) employing the electrochemical quartz crystal microbalance (EQCM). The present study aims at understanding how cathodic charge in n-doped poly-33″-DDTT is compensated. For this purpose, the in situ analysis of the variations of the polymeric mass has been considered. Poly-33″-DDTT was obtained as a thin coating onto a metallic substrate via the anodic coupling of the corresponding monomer 3,3″-didodecyl-2,2':5',2″-terthiophene (33″-DDTT). When subjected to electrochemical n-doping in the polarization interval -2.5 ≤ E _appl ≤ 0 V vs. Ag/Ag⁺, the films of poly-33″-DDTT varied their mass according to a mechanism of cations insertion during n-doping and cations extraction during polymer neutralization. In fact, the electrochemical doping of polythiophenes requires the accompanying exchange of charged species to maintain the electroneutrality within the structure of the polymer in all states of polarization. At the end of a full electrochemical cycle (consisting of the n-doping and the successive neutralization of poly-33″-DDTT), the polymer retains a fraction of the mass acquired during n-doping, thus manifesting the phenomena of mass trapping. The combined analysis of electrochemical and microgravimetric data suggests that poly-33″-DDTT in the n-doped state undergoes (or electrocatalyzes) uncontrolled electrochemical reactions that are not accompanied by mass variations.

Conjugated polymers as Langmuir and Langmuir-Blodgett films: Challenges and applications in nanostructured devices

Initially developed for classic systems composed of fatty acids and phospholipids, the Langmuir and Langmuir-Blodgett (LB) techniques allow the fabrication of nanometer-scale devices at self-assembly interfaces with high control over the thickness and molecular architecture. Their application in the research and production of new plastic materials has grown considerably over the past few decades due to the efficiency of conjugated polymers (CPs) for the production of light-emitting diodes, flexible displays, solar cells, and other photoelectronic devices. The structuring of polymers at different interfaces is not trivial as this class of macromolecules can undergo through different processes of folding/unfolding, which hinders the formation of stable Langmuir monolayers and, consequently, the production of Langmuir-Blodgett films. With these ideas in mind, the present article aims to review a series of elements related to the formation of stable Langmuir and Langmuir-Blodgett films of CPs, especially those based on poly(phenylene vinylene)s, polyfluorenes, and polythiophenes. This review is divided into two parts where we first discuss the formation of neat CP films, and then the strategies for the formation of stable CP films based on the co-immobilization with fatty acids, other polymers, and enzymes as mixed films.

Langmuir and Langmuir-Blodgett Films of Poly[(9,9-dioctylfluorene)-co-(3-hexylthiophene)] for Immobilization of Phytase: Possible Application as a Phytic Acid Sensor

In this work, the copolymer poly[(9,9-dioctylfluorene)-co-(3-hexylthiophene)] was employed as a matrix for immobilizing phytase, aiming at the detection of phytic acid. The copolymer was spread on the air-water interface forming Langmuir monolayers and phytase adsorbed from the aqueous subphase. The interactions between the copolymer and the enzyme components were investigated with surface pressure and surface potential-area isotherms, Brewster angle microscopy, and polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS). The enzyme could be incorporated in the monolayers from the aqueous subphase, expanding the copolymer films and maintaining its secondary structure. The polymeric films presented a morphological heterogeneous pattern at the air-water interface because of the ability of their chains to fold and entangle, causing inherent defects in the organization as well as unbalanced lateral distribution at the air-water interface because of the formation of aggregates. The interfacial films were transferred to solid supports as Langmuir-Blodgett films and characterized by PM-IRRAS and scanning electronic microscopy, which showed not only the co-transfer of the enzyme but also the maintenance of their heterogeneous morphological pattern. The enzymatic activity of the blended film was analyzed by UV-vis spectroscopy and allowed the estimation of the value of the Michaelis constant (13.08 mM), demonstrating the feasibility of the system to selectively detect phytic acid for biosensing purposes.

Chiral luminescent lanthanide complexes possessing strong (samarium, SmIII) circularly polarised luminescence (CPL), and their self-assembly into Langmuir-Blodgett films

The lanthanide directed self-assembly of chiral amphiphilic 2,6-pyridinedicarboxylic acid based ligands 1 and 2 with various Ln(CF₃SO₃)₃ (Ln = Tb^III, Sm^III, Lu^III, Dy^III) salts was studied in CH₃CN and evaluated with the expected 1 : 3 and 1 : 1 Ln : Ligand species forming in solution. Ligand chirality was retained and transferred, as depicted by circular dichroism (CD) and circularly polarised luminescence (CPL) measurements (for Tb^III and Sm^III), to the lanthanide centre upon complexation with high dissymmetry factor values for the Sm^III complexes obtained (g_lum = -0.44 and 0.29 and 0.45 and -0.23 for the ⁴G_5/2→⁶H_5/2 and the ⁴G_5/2→⁶H_7/2 transitions of Sm·1₃ and Sm·2₃, respectively). The ability of the complexes to form stable Langmuir monolayers at the air-water interface was also established while Langmuir-Blodgett films of Tb·L₃ and Sm·L₃ exhibited lanthanide luminescent emission.

Tailoring optical properties and stimulated emission in nanostructured polythiophene

Polythiophenes are the most widely utilized semiconducting polymers in organic electronics, but they are scarcely exploited in photonics due to their high photo-induced absorption caused by interchain polaron pairs, which prevents the establishment of a window of net optical gain. Here we study the photophysics of poly(3-hexylthiophene) configured with different degrees of supramolecular ordering, spin-coated thin films and templated nanowires, and find marked differences in their optical properties. Transient absorption measurements evidence a partially-polarized stimulated emission band in the nanowire samples, in contrast with the photo-induced absorption band observed in spin-coated thin films. In combination with theoretical modeling, our experimental results reveal the origin of the primary photoexcitations dominating the dynamics for different supramolecular ordering, with singlet excitons in the nanostructured samples superseding the presence of polaron pairs, which are present in the disordered films. Our approach demonstrates a viable strategy to direct optical properties through structural control, and the observation of optical gain opens the possibility to the use of polythiophene nanostructures as building blocks of organic optical amplifiers and active photonic devices.