Effect Of Side Chain Length Research Articles

Effects of sidechain length and composition on the kinetic conversion and product distribution of vitamin D analogs determined by real-time NMR

Novel pregna-5, 7-dienes were synthesized and subjected to UVB irradiation to generate the corresponding pre-D intermediates, tachysterol and lumisterol analogs. The kinetics of the conversion from each of the pre-D intermediates to the corresponding novel D analogs was investigated by using real time 1H NMR measurements inside the NMR magnet. Both the length and composition of the side chains were found to affect the rate of the kinetic conversion from pre-D intermediates to the thermodynamically more stable D analogs. Compound 7cc which has both a long side chain and a tertiary alcohol moiety showed the highest conversion rate, while compound 4a-S which has a very short side chain without the tertiary alcohol had the lowest conversion rate among the 13 tested compounds. We also determined product distributions for these 5,7-dienes upon UVB irradiation followed by thermodynamic equilibration. No clear correlations between product distribution and side chain length or composition were identifiable under the current experimental conditions, suggesting there are other factors affecting the kinetics during the photochemical reactions for these 5,7-dienes. To the best of our knowledge, this is the first time the influences of side chain length and composition on the real time conversion kinetics from pre-D to D are studied. This study could serve as step-stones in future kinetic studies of novel biologically active 5,7-dienes and their corresponding D analogs under more physiologically relevant ex vivo or in vivo conditions, as well as providing important insights into optimizing yields of the desired active products during their organic syntheses.

Excited-State Dynamics of Water-Soluble Polythiophene Derivatives: Temperature and Side-Chain Length Effects

We report synthesis and detailed spectroscopic study of three water-soluble polythiophene derivatives with distinct homologous oligo(ethylene oxide) side-chain lengths and lower critical solution temperatures (LCSTs). The linear absorption spectra exhibit reversible shifts and broadening with the variation of their aqueous solution temperature, whereas the corresponding steady-state fluorescence emission spectra were found to show negligible shifts and only minor changes in their line shape. Measurements of picosecond time-resolved fluorescence at chosen emission wavelengths reveal a strong dependence of the isotropic decays on both side-chain length and aqueous solution temperature. With lengthening of the side chain, the isotropic decays become not only remarkably slow but also increasingly complex. Except for the polymer with the shortest side chain, significant acceleration of the isotropic decays was found when the solution temperature was raised to the corresponding LCSTs and beyond, which further causes formation of large aggregates as evident by the physical appearance change from clear solutions to turbid suspensions. Direct evidence for a temperature-induced change of polymer chain conformation was obtained through measurements of time-resolved fluorescence anisotropies, which are characterized by a substantial increase of the initial values from ~0.2 to 0.4 and the appearance of a pronounced fast decay component with an estimated lifetime of 36 ps. The high initial anisotropy of ~0.4 observed for the two polymers with longer side-chains above their LCSTs suggests that the polymer chains are highly ordered in the aggregates. The observed effects of side-chain length and solution temperature are discussed by considering the conformational relaxation of the polymer backbones and occurrence of interchain energy transfer.

The Effect of Side-Chain Length on the Solid-State Structure and Optoelectronic Properties of Fluorene-alt-Benzothiadiazole Based Conjugated Polymers—A DFT Study

Using the dispersion corrected density functional theory (DFT-D/B97D) approach, we have performed bulk solid-state calculations to investigate the influence of side-chain length on the molecular packing and optoelectronic properties of poly (9,9-di-n-alkylfluorene-alt-benzothiadiazole) or FnBT's where n is the number of CH(2) units in the alkyl side-chains. Our results indicate that the FnBT's with longer side-chains in their most stable configurations, due to the significant intermolecular interactions between the side-chains, form lamellar crystal structures. On the other hand, for the FnBT's with shorter side-chains, two nearly degenerate stable crystal structures with nearly hexagonal symmetries have been found. These different packing structures can be attributed to the microphase separations between the flexible side-chains and the rigid backbones whose existence has been discussed in previous investigations for other hairy rod polymers. As a result of the efficient interchain interactions for the lamellar structures, the dihedral angle between the F and BT units is reduced by about 30°, providing a more planar configuration for the backbone. In turn, a more planar backbone leads to a decrease, about 0.2 and 0.3 eV, of the band gaps of the lamellar structures relative to the gap values for the gas and the nearly hexagonal phases, respectively. Time-dependent DFT (TD-DFT) was used to study the excited states of the monomers of FnBT's with various lengths of side-chains. TD-DFT study suggests that the absorption spectrum of the polymers with longer side-chains is red-shifted relative to the polymers with shorter side-chains and the gas phase.

Self-Assembly of Poly(4-vynil-N-alkylpyridinium) Bromide onto Silica: Effect of Side-Chain Length on Structural Aspects at a Molecular Level

Self-assembly of poly(4-vynil-N-alkyl)pyridinium bromide with alkyl side chains of 2, 5, 7, 10, or 16 carbons from ethanolic solutions onto flat silica surfaces was studied by means of ellipsometry, atomic force microscopy (AFM), contact angle measurements, and sum-frequency generation (SFG) vibrational spectroscopy in the CH3 and CH2 stretch region. Ab initio quantum-chemical calculations on the N-alkylpyridinium side-group with restricted Hartree–Fock (RHF) method and 6-311G (d,p) basis set were done to estimate the charge distribution along the pyridinium ring and the alkyl side-chain. SFG results showed that longer side chains promote the disorientation of the alkyl groups at the surface, corroborating with the contact angle values. AFM images revealed film homogeneity, regardless the alkyl side group. However, after 24 h contact with water, ringlike structures appeared on the film surfaces, when the polycation alkyl side chain had 7 or less carbons, and as the alkyl chain increased to 10 or 16 carbons, the films dewetted because the hydrophobic interactions prevailed over the electrostatic interactions between the pyridinium charged groups and the negatively charged SiO2 surface. Under acid conditions (HCl 0.1 mol·L–1), the film mean thickness values decreased up to 50% of original values when the alkyl side chains were ethyl or pentyl groups due to ion-pair disruption, but for longer groups they remained unchanged. Quantum-chemical optimization and Mulliken electron population showed that (i) from C2 to C15 the positive charge at the headgroup (HG) decreased 0.025, while the charge at combined HG + α-CH2 increased 0.037; and (ii) for C6 or longer, the alkyl side group presents a tilt in the geometry, moving away from the plane. Such effects summed up over the whole polymer chain give support to suggest that when the side chains are longer than 7 carbons, the hydrophobic interaction decreases film stability and increases acid resistance.

Rheo-Optical Study on Dynamics of Bottlebrush-Like Polymacromonomer Consisting of Polystyrene. II. Side Chain Length Dependence on Dynamical Stiffness of Main Chain

Dynamic birefringence and viscoelasticity measurements of bottlebrush-like polystyrene polymacromonomers having various branch (side chain) lengths were conducted over a wide frequency region covering from the glass-to-rubber transition zone to the flow zone in order to discuss effects of side chain length on dynamical stiffness of main polymer chain. Strain-induced birefringence at high frequencies was negative, similarly to linear polystyrenes, irrespective of side chain length, while birefringence in the flow zone strongly depended on side chain length. By using the modified stress-optical rule (MSOR), the complex modulus was decomposed into two components, main chain and branch components. With increasing the side chain length, the dynamical stiffness of main chain (number of repeating units per viscoelastic segment) first increased and then leveled off, suggesting that repulsive interaction between branches would be screened out over a certain branch length.

Thermal properties and crystallization behaviors of medium-chain-length poly(3-hydroxyalkanoate)s

Medium-chain-length poly(3-hydroxyalkanoate)s (mcl-P(3HA)s) with different side-chain length ranging from C3–C9 were synthesized from 2-alkenoic acids of C6–C12 by using a metabolically engineered strain of Escherichia coli. The effect of side-chain length of mcl-P(3HA)s on thermal properties and crystallization behaviors was investigated by DSC and X-ray analyses. All mcl-P(3HA)s formed a chain-packed crystalline structure in the solvent-cast films. Melting temperatures of solvent-cast film of mcl-P(3HA)s first decreased from 59 °C to 45 °C with the change of side-chain from C3 to C4 and thereafter increased to 69 °C with an extension of side-chain to C9. The X-ray diffraction patterns indicate the formation of a layered structure aligned the main-chains in planes involving side-by-side packing of side-chains with a periodic distance of 1.6–2.8 nm for the mcl-P(3HA)s with over C4 side-chain. The interlayer distance increased proportionally to the length of side-chain for the mcl-P(3HA)s with over C4 side-chain, while the corresponding value of mcl-P(3HA) with C3 side-chain was apparently deviated from the extrapolated line plotted the distance against side-chain length. These results indicate that the changeover in crystallization manner occurs between P(3HA)s with under C3 side-chain and with over C4 side-chain. For the mcl-P(3HA)s with side-chain carbon number over C7, two distinct phase transitions were happened during heating process from a melt-quenched amorphous state. At lower temperature region, the mcl-P(3HA) molecules formed a smectic liquid-crystalline structure owing to the side-chain interactions, and the structure was disrupted at temperatures between 20 and 50 °C. After the disruption of smectic aggregates, the crystallization of mcl-P(3HA) chains immediately occurred with participation of both main- and side-chains.

Self-assembly, optical and electrical properties of fork-tailed perylene bisimides

Effect of side-chain length on self-assembly, optical and electrochemical properties of N,N′-di(1-pentylbutyl)perylene-3,4,9,10-tetracarboxylic bisimide and N,N′-di(1-hexylpentyl)perylene-3,4,9,10-tetracarboxylic bisimide has been studied. The photo-physical, thermal and electrochemical properties were studied using UV–Vis and fluorescence, differential scanning calorimetry, and cyclic voltammetry, respectively. The molecules self-assembled as 1D – rods and molecular bundles, self-assembly was studied using SEM, optical and fluorescence microscopic techniques. The results concluded that the compound with short tail exhibits low solubility and self-assembled faster. The photo-physical properties of the compounds were not much affected by varying the alkyl chain length. The compounds geometries were optimized at 6-31G∗ using DFT and the potentials were correlated with molecular orbitals.

The effect of side-chain length on regioregular poly[3-(4-n-alkyl)phenylthiophene]/PCBM and ICBA polymer solar cells

The photovoltaic, charge transport, light absorption and morphology properties of a series of poly[3-(4-n-alkyl)phenylthiophene] (PAPT):acceptor (phenyl-C61-butyric acid methyl ester (PCBM) or indene-C60 bisadduct (ICBA)) blend films are reported as a function of alkyl side-chain length. Regioregular poly[3-(4-n-butyl)phenylthiophene] (PBPT), poly[3-(4-n-hexyl)phenylthiophene] (PHPT), poly[3-(4-n-octyl)phenylthiophene] (POPT), and poly[3-(4-n-decyl)phenylthiophene] (PDPT) were successfully synthesized by a modified Grignard metathesis (GRIM) polymerization method. The effects of the alkyl side-chain length on the optical, electrochemical and structural properties of the polymers were carefully investigated to establish a relationship between the molecular structure and device function. Bulk heterojunction solar cells made of PAPTs blended with either PCBM or ICBA showed a strong photovoltaic property dependence on the alkyl side-chain length. Among all PAPTs used in this study, the best performance was observed in PHPT-based devices. This is the first report of the use of PHPT in polymer solar cells. In addition, PAPT devices blended with ICBA generally showed higher open-circuit voltages (Voc) and power conversion efficiencies than PCBM-based devices. For example, a PHPT:ICBA photovoltaic device showed a Voc of 0.79 V and a power conversion efficiency of 3.7%, which is the highest performance reported thus far using PAPT polymers. While the optical properties of PAPT/electron acceptor films exhibit the strongest effect on the short-circuit current of the devices, a balance between the optical, electrical and morphological properties of blended films caused by the alkyl side-chain length determines the overall photovoltaic performance of these devices. Therefore, our work provides a fundamental understanding of the molecular structure–device function relationship, especially with respect to changes in the alkyl side-chain length in conjugated polymers.

Molecular Modeling of Folding in Lactam-Modified (Glutamate+Lysine Analog) Conotoxins

We report a method to model the conformational folding of α-conotoxins and the factors that affect the synthesis of specific regioisomers by using a combination of molecular dynamics methods to determine the geometric factors (S-S distances and C-N distances in lactam-modified α-conotoxins) and ab initio methods to determine the conformational energy and molecular orbital information. In the literature, the replacement of the Cys2-Cys7 disulfide bridge with a lactam bridge causes a complete loss of activity. However, exchanging the larger Cys3-Cys13 bridge leads to analogues that exhibit considerable affinities for the receptor sites. In previous work [Osysko et al. Biophys. J. 2011, 100, 155a], we studied the effect of side-chain length at position 13 by replacing this amino acid with modified lysines, where one to four methylene units would separate the alpha carbon and the ammonium group. Cys 3 was then replaced by aspartate. In this work, we examine a similar effect but replacing Cys3 with a glutamate residue instead. The results show that thermal fluctuations lead to configurations where a molecular orbital overlap between S-S atoms (Cys2-Cys7) can take place, leading to the proper regioisomer formation. Furthermore, ab initio methods predict adequate orbital overlap between the sulfur atoms. The length of the methylene chain of the basic amino acid at position 13 affects the probability of forming a lactam bridge between positions 7 and 13. Surprisingly, we find that the best overlap conditions are achieved for very short chains (only one methylene group separating the amino group and the alpha carbon) and, to a slightly smaller extent, for the longest chains (four methylene groups, i.e. lysine). Few overlap arrangements were observed in the simulations with two or three methylene groups.

Elasticity and safety of alkoxyethyl cyanoacrylate tissue adhesives

Cyanoacrylate glues are easily applied to wounds with good cosmetic results. However, they tend to be brittle and can induce local tissue toxicity. A series of cyanoacrylate monomers with a flexible ether linkage and varying side-chain lengths was synthesized and characterized for potential use as tissue adhesives. The effect of side-chain length on synthesis yield, physical and mechanical properties, formaldehyde generation, cytotoxicity in vitro and biocompatibility in vivo were examined. The incorporation of etheric oxygen allowed the production of flexible monomers with good adhesive strength. Monomers with longer side-chains were found to have less toxicity both in vitro and in vivo. Polymerized hexoxyethyl cyanoacrylate was more elastic than its commercially available and widely used alkyl analog 2-octyl cyanoacrylate, without compromising biocompatibility.

Modeling the Effect of Side-Chain Length on the Folding of Lactam-Modified Conotoxins

We developed a method to model the folding of α-conotoxins by combining molecular dynamics (to determine geometric factors relevant to folding) with ab initio calculations (for molecular orbital information). In previous work, [Kovacs et al. Biophys. J. 2010, 98, 636a], we followed literature suggestions to direct specific regioisomer formation by replacing the Cys3 with aspartate and the Cys13 thiol with an ammonium (-NH3+) group. The results were encouraging because we observed directionality towards the proper regioisomer folding, but we hypothesized that the short side chains at positions 3 and 13 resulted in brief contact times between the carboxyl and amino groups and no C-N overlap. Now, we evaluate this hypothesis’ validity by lengthening the side chain at position 13. We carried out equivalent calculations with two (vs one), three and four methylene units (-CH2-) between the alpha carbon and the ammonium group (four methylene units make this amino acid a lysine). The results show that thermal fluctuations lead to configurations where a molecular orbital overlap between S-S atoms (Cys2-Cys7) can take place, leading to the proper regioisomer formation. Furthermore, the amino acid proline appears to generate rigidity in its surrounding amino acids, specifically in at least the region controlling the relative orientation of the Cys2 and Cys7 residues. The length of the methylene chain of the basic amino acid at position 13 affects the probability of forming a lactam bridge between positions 3 and 13. With short chains (one methylene group), there never is any observed orbital overlap between the carbon and nitrogen atoms, possibly because of the rigidity of the backbone. The probability of robust overlap increases with chain length and matches the efficiency of the Cys2-Cys7 overlap when using lysine at position 13.

Effect of side chain length on structure and thermomechanical properties of fully substituted cellulose fatty esters

A series of cellulose esters (CEs) with high degrees of substitution has been obtained by linking aliphatic acid chlorides (from C8 to C18) onto cellulose backbone, in a homogeneous LiCl/DMAc medium. These materials have been characterized by Fourier transformed infra red (FTIR) and nuclear magnetic resonance of proton ( 1H NMR) spectroscopies, as well as differential scanning calorimetry (DSC), wide angle X-ray scattering (WAXS), dynamic mechanical analysis (DMA) and mechanical analyses. CEs organize in a layered type structure: cellulosic backbones are arranged in a plane, the flexible side chains being fully extended and perpendicular to the cellulosic backbone. When the fatty chain length exceeds 12 carbon atoms, a fraction of the alkyl chains crystallize into hexagonal packing. Regarding the mechanical behavior, the strain at break decreases significantly whereas no clear evolution of the yield stress is observed when the length of the lateral chain is increased.

Effects of Monomer Composition on CO2−Selective Polymer Brush Membranes

Membranes that contain a high fraction of amorphous poly(ethylene glycol) (PEG) are attractive for selective removal of CO2 from H2 streams, but crystallization of PEG chains restricts both flux and selectivity. The high thickness of solution-cast membranes also limits flux. This study demonstrates the formation of composite, PEG-containing membranes through atom transfer radical polymerization of poly(ethylene glycol methyl ether methacrylate) from initiator-modified, porous substrates. The resulting membrane skins are only 50−500 nm thick, and copolymers that contain a mixture of short and long PEG side chains do not readily crystallize. The smaller PEG chains (8−9 ethylene oxide units) prevent crystallization, while the presence of longer side chains (23−24 ethylene oxide units) allows the membranes to maintain a CO2/H2 selectivity of 12 at room temperature. This work examines the effect of side-chain length on polymerization rate as well as the permeability, selectivity, and crystallinity of copolymer...

Modeling of Bottle-Brush Polymer Adsorption onto Mica and Silica Surfaces: Effect of Side-Chain Length

Adsorption of a series of charged bottle-brush polymers with side chains of different length on solid surfaces is modeled using a lattice mean-field theory. The bottle-brush polymers are modeled Lis being composed of two types of main-chain segments: charged segments and uncharged segments with ill attached side chain. The composition variable X denotes the percentage of charged main-chain segments and ranges from X = 0 (uncharged bottle-brush polymer) to X = 100 (linear polyelectrolyte). Two types of surfaces are considered: mica-like and silica-like. The mica-like surface possesses a constant negative surface charge density and no nonelectrostatic affinity for either main-chain or side-chain segments, whereas the silica-like Surface has a constant negative surface potential and a positive affinity for the side chains of the bottle-brush polymers. With the mica-like Surface. ill low X the surface excess becomes smaller and at X >= 25 it becomes larger with increasing side-chain length. Hence, the value of X at which the surface excess displays a maximum increases with the side-chain length. However, with the silica-like Surface the surface excess increases with increasing side-chain length at all X < 100, and the maximum of the surface excess appears at X approximate to 10 independent of the side-chain length.

Effect of alkyl side chain length on the properties of polyetherimides from molecular simulation combined with experimental results

AbstractThree polyetherimides (PEIs) with the same backbone of Ultem 100 but different lengths of the alkyl side chains were simulated by using molecular dynamics and molecular mechanics techniques to investigate the effect of side chain length on their properties and physical mechanism behind. Simulation results, which are consistent to the experimental data, show that PEI‐5 with four methylene units in each alkyl side chain has higher Tg (glass transition temperature) and higher tensile strength, but lower tensile elongation at break than those of PEI‐6 with five and PEI‐8 with seven methylene units in each alkyl side chain. However, unlike the traditional phenomena, conformational analysis provides that PEI‐5 with the highest Tg gives the highest flexibility to the polymer chain, whereas PEI‐8 with the lowest Tg imparts the lowest flexibility resulting from attachment of longer alkyl side chain increase the rigidity of backbone. From the calculated ratio of the accessible volume to the total volume for each system, the highest ratio of PEI‐8 indicates that long alkyl side chains generate more free volume than short side chains, acting as an internal plasticizer in bulk structure. It is the internal plasticizing effect that is predominantly responsible for the abnormal properties, instead of the rigidity from side chains. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 595–599, 2010

Well-defined, high molecular weight poly(3-alkylthiophene)s in thin-film transistors: side chain invariance in field-effect mobility

In this paper, the effect of side chain length on transistor performance was analyzed by using a series of well-defined, regioregular poly(3-alkylthiophene) (P3AT) samples (with PDI values as low as 1.1). Both untreated and octyltrichlorosilane-treated (OTS) SiO2 transistor dielectric layers were compared for all samples. On untreated SiO2, P3AT with hexyl side chains showed the best mobility, with mobilities as high as 0.1 cm2 V−1 s−1, and mobility values then decreased slightly with longer side-chain length. When using OTS-8 treated SiO2, on the other hand, mobility values remained high even with polymers of longer side-chain length, obtaining mobilities as high as 0.2 cm2 V−1 s−1 for hexyl, octyl and dodecyl side chains, which were much higher than previously reported values. Carrier mobilities of P3ATs with longer side chains were seen to be more sensitive to surface chemistry than for P3ATs with shorter side chains. Using morphological and GIXS studies, we found that for longer side chains, self-assembly is governed by two competing processes—backbone packing (π-stacking) and side-chain packing—that resulted in polymorphic behavior and disorder. On an OTS-treated surface, interactions between dielectric surface and side chains were reduced, resulting in better order at the interface and higher mobility.

The Effect of Side Chain Length and Hydrogen Bonding on the Viscoelastic Property of Isobutene/Maleimide Copolymers

AbstractThe viscoelastic properties of the alternating copolymers of N‐substituted maleimides with n‐alkyl and ω‐carboxy‐n‐alkyl groups as the N‐substituent with isobutene were investigated by dynamic mechanical analysis. The transition temperatures in the α‐relaxation region depended on the alkyl chain length and the presence or absence of a terminal carboxy group in the side chain. β‐Relaxation due to side chain dynamics was also observed in a lower temperature region without merging the α‐ and β‐relaxation processes for all the copolymers. The molecular motions of the semiflexible main chain and the flexible side alkyl groups were investigated as well as the intermolecular interaction by hydrogen bonding of the carboxyl groups.magnified image

Effect of the length of the side chains of comb-like copolymer dispersants on dispersion and rheological properties of concentrated cement suspensions

Two different groups of comb-like copolymer dispersants with side chain lengths ranging from 8 to 48 were synthesized and characterized: one group with the carboxylic content per mole molecule constant and the other group with the carboxylic contents per gram polymer constant. The effects of side chain length on comb-like copolymers on adsorption, dispersion, rheological behavior, and zeta potential for cement suspensions were investigated systematically to elucidate the governing dispersing mechanism. The adsorption of comb-like copolymer on the cement surfaces, controlled by COO − content in copolymer backbones, side chain length, and also polymer conformation in solution, governs the dispersion and rheological behavior of the cementitious system. The dispersion effect increases with the adsorbed amount; especially the adsorbed side chain density increases. But the dispersion power of comb-like copolymers varies depending on the side chain length in comb-like copolymer. The long side chain polymer has higher dispersion power than the shorter ones due to the stronger steric hindrance effect of the former; for the short side chain polymer with high ionic content, the electrostatic repulsion and steric hindrance together should be responsible for its dispersion effect. Such information also suggests that their exists the geometrical balance between the main chain and the side chains in comb-like copolymer dispersants which should be very useful in designing optimum molecular structures of high efficient dispersants.

Effect of Side-chain Length on the Side-chain Dynamics of α-Helical Poly(l-glutamic acid) as Probed by a Fluorescence Blob Model

Two series of pyrene-labeled poly(glutamic acid) (Py-PGA) were synthesized utilizing two different linkers for pyrene attachment, namely 1-pyrenemethylamine (PMA) and 1-pyrenebutylamine (PBA). Several Py-PGAs were synthesized for each series with pyrene contents ranging from 4 to 15 mol %. Py-PGA forms a rigid alpha-helix in DMF that effectively locks the backbone in place, thus enabling only side-chain or linker motions to be monitored by time-resolved fluorescence. Time-resolved fluorescence decays were acquired for the pyrene monomer of the Py-PGA constructs and the fluorescence blob model (FBM) was used to quantify the dynamics of the different linkers connecting pyrene to the backbone. Nitromethane was used to shorten the lifetime of the pyrene monomer, in effect controlling the probing time of the pyrene group, from 50 to 155 ns for PGA-PBA and from 50 to 215 ns for PGA-PMA. The FBM analysis of the fluorescence decays led to the conclusion that excimer formation around the rigid alpha-helix backbone takes place in a compact environment. The number of glutamic acid units within a blob, N blob, decreased only slightly with decreasing probing time for both Py-PGA constructs as a result of the compact distribution of the chromophores around the alpha-helix. The PGA alpha-helix was modeled using Hyperchem software and the ability of two pyrene groups to encounter was evaluated as they were separated by increasing numbers of amino acids along the alpha-helix. The number of amino acids required for two pyrenes to lose their ability to overlap and form excimer matched closely the N blob values retrieved using the FBM.

Effect of side chain length on the electrochemical and photoresponse characteristics of poly[3-(2′,5′-dialkoxyphenyl)thiophenes

Poly[3-(2′,5′-dioctyloxyphenyl)thiophene] (PDOOPT), poly[3-(2′,5′-diheptyloxyphenyl)thiophene] (PDHOPT) and poly[3-(2′,5′-dibutyloxyphenyl)-thiophene] (PDBOPT) have been prepared electrochemically from their monomers within nanocrystalline titanium dioxide (nc-TiO 2) porous surface deposited on indium doped tin oxide coated glass (ITO-glass) for solar cell application. The redox properties of the polymers were characterized using cyclic voltammetry. The energy levels of the highest occupied molecular orbitals (HOMO) and the lowest unoccupied molecular orbitals (LUMO) have been estimated from their cyclic voltammograms and UV–vis absorption spectra. The poly[3-(2′,5′-dialkoxyphenyl)thiophenes] studied sensitize nc-TiO 2 in liquid-state photoelectrochemical cells. Devices that consist of PDBOPT/nc-TiO 2 photoactive electrode showed improved performance over those that consist of PDHOPT/nc-TiO 2 and PDOOPT/nc-TiO 2. PDBOPT/nc-TiO 2 based devices produced an open-circuit voltage of 0.56 V, a short-circuit current of 45 μA/cm 2, and a fill factor of 0.52 when illuminated with white light intensity of 80 mW/cm 2.