Limiting factors for charge generation in low-offset fullerene-based organic solar cells.

Free charge generation after photoexcitation of donor or acceptor molecules in organic solar cells generally proceeds via (1) formation of charge transfer states and (2) their dissociation into charge separated states. Research often either focuses on the first component or the combined effect of both processes. Here, we provide evidence that charge transfer state dissociation rather than formation presents a major bottleneck for free charge generation in fullerene-based blends with low energetic offsets between singlet and charge transfer states. We investigate devices based on dilute donor content blends of (fluorinated) ZnPc:C60 and perform density functional theory calculations, device characterization, transient absorption spectroscopy and time-resolved electron paramagnetic resonance measurements. We draw a comprehensive picture of how energies and transitions between singlet, charge transfer, and charge separated states change upon ZnPc fluorination. We find that a significant reduction in photocurrent can be attributed to increasingly inefficient charge transfer state dissociation. With this, our work highlights potential reasons why low offset fullerene systems do not show the high performance of non-fullerene acceptors.

Synthesis of Deuterated and Sulfurated Polymers by Inverse Vulcanization: Engineering Infrared Transparency via Deuteration.

The synthesis of deuterated, sulfurated, proton-free, glassy polymers offers a route to optical polymers for infrared (IR) optics, specifically for midwave IR (MWIR) photonic devices. Deuterated polymers have been utilized to enhance neutron cross-sectional contrast with proteo polymers for morphological neutron scattering measurements but have found limited utility for other applications. We report the synthesis of perdeuterated d14-(1,3-diisopropenylbenzene) with over 99% levels of deuteration and the preparation of proton-free, perdeuterated poly(sulfur-random-d14-(1,3-diisopropenylbenzene)) (poly(S-r-d14-DIB)) via inverse vulcanization with elemental sulfur. Detailed structural analysis and quantum computational calculations of these reactions demonstrate significant kinetic isotope effects, which alter mechanistic pathways to form different copolymer microstructures for deutero vs proteo poly(S-r-DIB). This design also allows for molecular engineering of MWIR transparency by shifting C-H bond vibrations around 3.3 µm/3000 cm-1 observed in proteo poly(S-r-DIB) to 4.2 µm/2200 cm-1. Furthermore, the fabrication of thin-film MWIR optical gratings made from molding of deuterated-sulfurated, proton-free poly(S-r-d14-DIB) is demonstrated; operation of these gratings at 3.39 µm is achieved successfully, while the proteo poly(S-r-DIB) gratings are opaque at these wavelengths, highlighting the promise of MWIR sensors and compact spectrometers from these materials.

On the Mechanism of the Inverse Vulcanization of Elemental Sulfur: Structural Characterization of Poly(sulfur-random-(1,3-diisopropenylbenzene)).

Organosulfur polymers, such as those derived from elemental sulfur, are an important new class of macromolecules that have recently emerged via the inverse vulcanization process. Since the launching of this new field in 2013, the development of new monomers and organopolysulfide materials based on the inverse vulcanization process is now an active area in polymer chemistry. While numerous advances have been made over the last decade concerning this polymerization process, insights into the mechanism of inverse vulcanization and structural characterization of the high-sulfur-content copolymers that are produced remain challenging due to the increasing insolubility of the materials with a higher sulfur content. Furthermore, the high temperatures used in this process can result in side reactions and complex microstructures of the copolymer backbone, complicating detailed characterization. The most widely studied case of inverse vulcanization to date remains the reaction between S8 and 1,3-diisopropenylbenzene (DIB) to form poly(sulfur-random-1,3-diisopropenylbenzene)(poly(S-r-DIB)). Here, to determine the correct microstructure of poly(S-r-DIB), we performed comprehensive structural characterizations of poly(S-r-DIB) using nuclear magnetic resonance spectroscopy (solid state and solution) and analysis of sulfurated DIB units using designer S-S cleavage polymer degradation approaches, along with complementary de novo synthesis of the sulfurated DIB fragments. These studies reveal that the previously proposed repeating units for poly(S-r-DIB) were incorrect and that the polymerization mechanism of this process is significantly more complex than initially proposed. Density functional theory calculations were also conducted to provide mechanistic insights into the formation of the derived nonintuitive microstructure of poly(S-r-DIB).

Towards Efficient and Stable Donor-Acceptor Luminescent Radicals.

In contrast to closed-shell luminescent molecules, the electronic ground state and lowest excited state in organic luminescent radicals are both spin doublet, which results in spin-allowed radiative transitions. Most reported luminescent radicals with high photoluminescent quantum efficiency (PLQE) have a donor-acceptor (D-A•) chemical structure where an electron-donating group is covalently attached to an electron-withdrawing radical core (A•). Understanding the main factors that define the efficiency and stability of D-A• type luminescent radicals remains challenging. Here, we designed and synthesized a series of tri(2,4,6-trichlorophenyl)methyl (TTM) radical derivatives with donor substituents varying by their extent of conjugation and their number of imine-type nitrogen atoms. The experimental results suggest that the luminescence efficiency and stability of the radicals are proportional to the degree of conjugation but inversely proportional to the number of imine nitrogen atoms in the substituents. These experimental trends are very well reproduced by density functional theory calculations. The theoretical results indicate that both the luminescence efficiency and radical stability are related to the energy difference between the charge transfer (CT) and local-excitation (LE) states, which decreases as either the number of imine nitrogen atoms in the substituent increases or its conjugation length decreases.

Ion-modulated radical doping of spiro-OMeTAD for more efficient and stable perovskite solar cells.

Record power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) have been obtained with the organic hole transporter 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenyl-amine)9,9'-spirobifluorene (spiro-OMeTAD). Conventional doping of spiro-OMeTAD with hygroscopic lithium salts and volatile 4-tert-butylpyridine is a time-consuming process and also leads to poor device stability. We developed a new doping strategy for spiro-OMeTAD that avoids post-oxidation by using stable organic radicals as the dopant and ionic salts as the doping modulator (referred to as ion-modulated radical doping). We achieved PCEs of >25% and much-improved device stability under harsh conditions. The radicals provide hole polarons that instantly increase the conductivity and work function (WF), and ionic salts further modulate the WF by affecting the energetics of the hole polarons. This organic semiconductor doping strategy, which decouples conductivity and WF tunability, could inspire further optimization in other optoelectronic devices.

Impact of secondary donor units on the excited-state properties and thermally activated delayed fluorescence (TADF) efficiency of pentacarbazole-benzonitrile emitters.

The performance of organic light-emitting diodes based on thermally activated delayed fluorescence emitters depends on the efficiency of reverse intersystem crossing (RISC) processes, which are promoted by a small energy gap between the lowest singlet (S1) and triplet (T1) excited states and large spin-orbit couplings. Recently, it was proposed that the introduction of secondary donor units into 2,3,4,5,6-penta(9H-carbazol-9-yl)benzonitrile (5CzBN) can significantly increase the mixing between triplet states with charge-transfer (CT) and local-excitation characteristics and consequently increase the spin-orbit couplings. Here, the results of long-range corrected density functional theory calculations show that the main impact on the RISC rates of substituting 5CzBN with secondary donors is due to a decrease in adiabatic singlet-triplet energy gaps and intramolecular reorganization energies rather than to a change in spin-orbit couplings. Our calculations underline that at least two singlet and three triplet excited states contribute to the ISC/RISC processes in 5CzBN and its derivatives. In addition, we find that in all emitters, the lowest singlet excited-state potential energy surface has a double-minimum shape.

Organic Neutral Radical Emitters: Impact of Chemical Substitution and Electronic-State Hybridization on the Luminescence Properties.

Neutral donor-acceptor (D-A•) organic radicals have recently attracted a great deal of attention as promising luminescent materials due to their strong doublet emission. Here, we consider a series of emitters based on substituted triarylamine (TAA) donors and a radical-carrying perchlorotriphenylmethyl (PTM) acceptor. We evaluate, by means of quantum-chemical calculations and theoretical modeling, how chemical substitution affects the electronic structures and radiative and nonradiative decay rates. Our calculations show that the radiative decay rates are dominated in all instances by the electronic coupling between the lowest excited state, which has charge-transfer (CT) character, and the ground state. On the other hand, the nonradiative decay rates in the case of TAA-PTM radicals that have high CT energies are defined by the electronic hybridization of the CT state with local excitations (LE) on the PTM moiety; also, these nonradiative rates deviate significantly from the gap law dependence that is observed in the TAA-PTM radicals that have low CT energies. These findings underscore that hybridization of the emissive state with high-energy states can, in analogy with the intensity borrowing effect commonly invoked for radiative transitions, enhance as well the nonradiative decay rates. Our results highlight that in order to understand the emissive properties of D-A• radicals, it is required that the electronic hybridization of the CT states with both the ground and the LE states be properly considered.

Electronic Structure of Multicomponent Organic Molecular Materials: Evaluation of Range-Separated Hybrid Functionals.

Range-separated hybrid (RSH) functionals have become a tool of choice to study the intra- and inter-molecular electronic states in organic materials. These functionals provide the most accurate descriptions of the electronic structure when the range-separation parameter is optimally tuned (OT). However, since the range-separation parameter is molecule dependent, this approach faces consistency issues when applied to the multicomponent systems typically found in the active layers of organic solar cells or organic light-emitting diodes (OLEDs). Here, we investigate the performance of four common RSH functionals in the description of the excited states of three molecular compounds used as components of the active layer in a hyperfluorescence OLED device. Our results indicate that the excited-state energies of the investigated molecules show a very weak dependence on the range-separation parameter value when they are evaluated by means of a screened version of RSH functionals. In this instance, the excited states of all three molecular compounds can be derived accurately and consistently with the exact same functional.

Spherical Macroporous Carbon Nanotube Particles with Ultrahigh Sulfur Loading for Lithium-Sulfur Battery Cathodes.

A carbon host capable of effective and uniform sulfur loading is the key for lithium-sulfur batteries (LSBs). Despite the application of porous carbon materials of various morphologies, the carbon hosts capable of uniformly impregnating highly active sulfur is still challenging. To address this issue, we demonstrate a hierarchical pore-structured CNT particle host containing spherical macropores of several hundred nanometers. The macropore CNT particles (M-CNTPs) are prepared by drying the aerosol droplets in which CNTs and polymer particles are dispersed. The spherical macropore greatly improves the penetration of sulfur into the carbon host in the melt diffusion of sulfur. In addition, the formation of macropores greatly develops the volume of the micropore between CNT strands. As a result, we uniformly impregnate 70 wt % sulfur without sulfur residue. The S-M-CNTP cathode shows a highly reversible capacity of 1343 mA h g-1 at a current density of 0.2 C even at a high sulfur content of 70 wt %. Upon a 10-fold current density increase, a high capacity retention of 74% is observed. These cathodes have a higher sulfur content than those of conventional CNT hosts but nevertheless exhibit excellent performance. Our CNTPs and pore control technology will advance the commercialization of CNT hosts for LSBs.

2q37 Deletion syndrome confirmed by high-resolution cytogenetic analysis.

Chromosome 2q37 deletion syndrome is a rare chromosomal disorder characterized by mild to moderate developmental delay, brachydactyly of the third to fifth digits or toes, short stature, obesity, hypotonia, a characteristic facial appearance, and autism spectrum disorder. Here, we report on a patient with 2q37 deletion presenting with dilated cardiomyopathy (DCMP). Congenital heart malformations have been noted in up to 20% of patients with 2q37 deletions. However, DCMP has not been reported in 2q37 deletion patients previously. The patient exhibited the characteristic facial appearance (a flat nasal bridge, deep-set eyes, arched eyebrows, and a thin upper lip), developmental delay, mild mental retardation, peripheral nerve palsy, and Albright hereditary osteodystrophy (AHO)-like phenotypes (short stature and brachydactyly). Conventional chromosomal analysis results were normal; however, microarray-based comparative genomic hybridization revealed terminal deletion at 2q37.1q37.3. In addition, the patient was confirmed to have partial growth hormone (GH) deficiency and had shown a significant increase in growth rate after substitutive GH therapy. Chromosome 2q37 deletion syndrome should be considered in the differential diagnosis of patients presenting with AHO features, especially in the presence of facial dysmorphism. When patients are suspected of having a 2q37 deletion, high-resolution cytogenetic analysis is recommended.

Investigation of Thermally Induced Degradation in CH3NH3PbI3 Perovskite Solar Cells using In-situ Synchrotron Radiation Analysis.

In this study, we employ a combination of various in-situ surface analysis techniques to investigate the thermally induced degradation processes in MAPbI3 perovskite solar cells (PeSCs) as a function of temperature under air-free conditions (no moisture and oxygen). Through a comprehensive approach that combines in-situ grazing-incidence wide-angle X-ray diffraction (GIWAXD) and high-resolution X-ray photoelectron spectroscopy (HR-XPS) measurements, we confirm that the surface structure of MAPbI3 perovskite film changes to an intermediate phase and decomposes to CH3I, NH3, and PbI2 after both a short (20 min) exposure to heat stress at 100 °C and a long exposure (>1 hour) at 80 °C. Moreover, we observe clearly the changes in the orientation of CH3NH3+ organic cations with respect to the substrate in the intermediate phase, which might be linked directly to the thermal degradation processes in MAPbI3 perovskites. These results provide important progress towards improved understanding of the thermal degradation mechanisms in perovskite materials and will facilitate improvements in the design and fabrication of perovskite solar cells with better thermal stability.

In Situ Spectroscopic and Computational Studies on a MnO2-CuO Catalyst for Use in Volatile Organic Compound Decomposition.

In situ near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and density functional theory calculations were conducted to demonstrate the decomposition mechanism of propylene glycol methyl ether acetate (PGMEA) on a MnO2-CuO catalyst. The catalytic activity of MnO2-CuO was higher than that of MnO2 at low temperatures, although the pore properties of MnO2 were similar to those of MnO2-CuO. In addition, whereas the chemical state of MnO2 remained constant following PGMEA dosing at 150 °C, MnO2-CuO was reduced under identical conditions, as confirmed by in situ NEXAFS spectroscopy. These results indicate that the presence of Cu in the MnO2-CuO catalyst enables the release of oxygen at lower temperatures. More specifically, the released oxygen originated from the Mn-O-Cu moiety on the top layer of the MnO2-CuO structure, as confirmed by calculation of the oxygen release energies in various oxygen positions of MnO2-CuO. Furthermore, the spectral changes in the in situ NEXAFS spectrum of MnO2-CuO following the catalytic reaction at 150 °C corresponded well with those of the simulated NEXAFS spectrum following oxygen release from Mn-O-Cu. Finally, after the completion of the catalytic reaction, the quantities of lactone and ether functionalities in PGMEA decreased, whereas the formation of C=C bonds was observed.

A Phase II Study of Poziotinib in Patients with Epidermal Growth Factor Receptor (EGFR)-Mutant Lung Adenocarcinoma Who Have Acquired Resistance to EGFR-Tyrosine Kinase Inhibitors.

PURPOSE: We examined the efficacy of poziotinib, a second-generation epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitor (TKI) in patients with lung adenocarcinoma with activating EGFR mutations, who developed acquired resistance (AR) to EGFR-TKIs. MATERIALS AND METHODS: This single-arm phase II study included EGFR-mutant lung adenocarcinoma with AR to erlotinib or gefitinib based on the Jackman criteria. Patients received poziotinib 16 mg orally once daily in a 28-day cycle. The primary endpoint was progression-free survival (PFS). Prestudy tumor biopsies and blood samples were obtained to determine resistance mechanisms. RESULTS: Thirty-nine patients were treated. Tumor genotyping was determined in 37 patients; 19 EGFR T790M mutations and two PIK3CA mutations were detected in the prestudy tumors, and seven T790M mutations were detected in the plasma assay. Three (8%; 95% confidence interval [CI], 2 to 21) and 17 (44%; 95% CI, 28 to 60) patients had partial response and stable disease, respectively. The median PFS and overall survival were 2.7 months (95% CI, 1.8 to 3.7) and 15.0 months (95% CI, 9.5 to not estimable), respectively. A longer PFS was observed for patients without T790M or PIK3CA mutations in tumor or plasma compared to those with these mutations (5.5 months vs. 1.8 months, p=0.003). The most frequent grade 3 adverse events were rash (59%), mucosal inflammation (26%), and stomatitis (18%). Most patients required one (n=15) or two (n=15) dose reductions. CONCLUSION: Low activity of poziotinib was detected in patients with EGFR-mutant non-small cell lung cancer who developed AR to gefitinib or erlotinib, potentially because of severe-toxicityimposed dose limitation.

Clinical and endocrine characteristics and genetic analysis of Korean children with McCune-Albright syndrome: a retrospective cohort study.

BACKGROUND: McCune-Albright syndrome (MAS) is a rare disease defined by the triad of fibrous dysplasia (FD), café au lait spots, and peripheral precocious puberty (PP). Because of the rarity of this disease, only a few individuals with MAS have been reported in Korea. We describe the various clinical and endocrine manifestations and genetic analysis of 14 patients with MAS in Korea. METHODS: Patients' clinical data-including peripheral PP, FD, and other endocrine problems-were reviewed retrospectively. In addition, treatment experiences of letrozole in five patients with peripheral PP were described. Mutant enrichment with 3'-modified oligonucleotides - polymerase chain reaction (MEMO-PCR) was performed on eight patients to detect mutation in GNAS using blood. MEMO-PCR is a simple and practical method that enables the nondestructive selection and enrichment of minor mutant alleles in blood. RESULTS: The median age at diagnosis was 5 years 2 months (range: 18 months to 16 years). Eleven patients were female, and three were male. Thirteen patients showed FD. All female patients showed peripheral PP at onset, and three patients subsequently developed central PP. There was a significant decrease in estradiol levels after two years of letrozole treatment. However, bone age was advanced in four patients. Two patients had clinical hyperthyroidism, and two patients had growth hormone (GH) excess with pituitary microadenoma. c.602G > A (p.Arg201His) in GNAS was detected in two patients in blood, and c.601C > T (p.Arg201Cys) in GNAS was detected in one patient in pituitary adenoma. CONCLUSIONS: This study described the various clinical manifestations of 14 patients with MAS in a single center in Korea. This study first applied MEMO-PCR on MAS patients to detect GNAS mutation. Because a broad spectrum of endocrine manifestations could be found in MAS, multiple endocrinopathies should be monitored in MAS patients. Better treatment options for peripheral PP with MAS are needed.

In Situ Thermal Decomposition of Exfoliated Two-Dimensional Black Phosphorus.

With a semiconducting band gap and high charge carrier mobility, two-dimensional (2D) black phosphorus (BP)­often referred to as phosphorene­holds significant promise for next generation electronics and optoelectronics. However, as a 2D material, it possesses a higher surface area to volume ratio than bulk BP, suggesting that its chemical and thermal stability will be modified. Herein, an atomic-scale microscopic and spectroscopic study is performed to characterize the thermal degradation of mechanically exfoliated 2D BP. From in situ scanning/transmission electron microscopy, decomposition of 2D BP is observed to occur at ∼400 °C in vacuum, in contrast to the 550 °C bulk BP sublimation temperature. This decomposition initiates via eye-shaped cracks along the [001] direction and then continues until only a thin, amorphous red phosphorus like skeleton remains. In situ electron energy loss spectroscopy, energy-dispersive X-ray spectroscopy, and energy-loss near-edge structure changes provide quantitative insight into this chemical transformation process.

Optimal cut-off value of perfusion parameters for diagnosing prostate cancer and for assessing aggressiveness associated with Gleason score.

To determine cut-off value of dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) parameters for differentiation of prostate malignant from benign and cancer with high-grade Gleason score (GS) (GS>7) from low-grade GS (GS≤7), 35 patients (24 malignant and 11 benign) who underwent DCE-MRI were included. Difference between malignant and benign was statistically significant for all magnetic resonance parameters except Ve. The cut-off values were K(trans)=0.184min(-1), Kep=0.695min(-1), iAUC=4.219mmol/l/min, and ADC=1340.5mm(2)/s. A significant difference in mean values of K(trans) and Kep between cancer with high-grade GS and low-grade GS was also observed. K(trans) and Kep showed a significant correlation with GS.

Effective passivation of exfoliated black phosphorus transistors against ambient degradation.

Unencapsulated, exfoliated black phosphorus (BP) flakes are found to chemically degrade upon exposure to ambient conditions. Atomic force microscopy, electrostatic force microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy are employed to characterize the structure and chemistry of the degradation process, suggesting that O2 saturated H2O irreversibly reacts with BP to form oxidized phosphorus species. This interpretation is further supported by the observation that BP degradation occurs more rapidly on hydrophobic octadecyltrichlorosilane self-assembled monolayers and on H-Si(111) versus hydrophilic SiO2. For unencapsulated BP field-effect transistors, the ambient degradation causes large increases in threshold voltage after 6 h in ambient, followed by a ∼ 10(3) decrease in FET current on/off ratio and mobility after 48 h. Atomic layer deposited AlOx overlayers effectively suppress ambient degradation, allowing encapsulated BP FETs to maintain high on/off ratios of ∼ 10(3) and mobilities of ∼ 100 cm(2) V(-1) s(-1) for over 2 weeks in ambient conditions. This work shows that the ambient degradation of BP can be managed effectively when the flakes are sufficiently passivated. In turn, our strategy for enhancing BP environmental stability will accelerate efforts to implement BP in electronic and optoelectronic applications.

Use of X-ray diffraction, molecular simulations, and spectroscopy to determine the molecular packing in a polymer-fullerene bimolecular crystal.

The molecular packing in a polymer: fullerene bimolecular crystal is determined using X-ray diffraction (XRD), molecular mechanics (MM) and molecular dynamics (MD) simulations, 2D solid-state NMR spectroscopy, and IR absorption spectroscopy. The conformation of the electron-donating polymer is significantly disrupted by the incorporation of the electron-accepting fullerene molecules, which introduce twists and bends along the polymer backbone and 1D electron-conducting fullerene channels.

Chemical characterization of DNA-immobilized InAs surfaces using X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure.

Single-stranded DNA immobilized on an III-V semiconductor is a potential high-sensitivity biosensor. The chemical and electronic changes occurring upon the binding of DNA to the InAs surface are essential to understanding the DNA-immobilization mechanism. In this work, the chemical properties of DNA-immobilized InAs surfaces were determined through high-resolution X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS). Prior to DNA functionalization, HF- and NH(4)OH- based aqueous etches were used to remove the native oxide from the InAs surface. The initial chemical state of the surface resulting from these etches were characterized prior to functionalization. F-tagged thiolated single-stranded DNA (ssDNA) was used as the probe species under two different functionalization methods. The presence of DNA immobilized on the surface was confirmed from the F 1s, N 1s, and P 2p peaks in the XPS spectra. The presence of salt had a profound effect on the density of immobilized DNA on the InAs surface. To study the interfacial chemistry, the surface was treated with thiolated ssDNA with and without the mercaptohexanol molecule. An analysis of the As 3d and In 3d spectra indicates that both In-S and As-S are present on the surface after DNA functionalization. The amount of In-S and As-S was determined by the functionalization method as well as the presence of mercaptohexanol during functionalization. The orientation of the adsorbed ssDNA is determined by polarization-dependent NEXAFS utilizing the N K-edge. The immobilized ssDNA molecule has a preferred tilt angle with respect to the substrate normal, but with a random azimuthal distribution.

Three-dimensional packing structure and electronic properties of biaxially oriented poly(2,5-bis(3-alkylthiophene-2-yl)thieno[3,2-b]thiophene) films.

We use a systematic approach that combines experimental X-ray diffraction (XRD) and computational modeling based on molecular mechanics and two-dimensional XRD simulations to develop a detailed model of the molecular-scale packing structure of poly(2,5-bis (3-tetradecylthiophene-2-yl)thieno[3,2-b]thiophene) (PBTTT-C(14)) films. Both uniaxially and biaxially aligned films are used in this comparison and lead to an improved understanding of the molecular-scale orientation and crystal structure. We then examine how individual polymer components (i.e., conjugated backbone and alkyl side chains) contribute to the complete diffraction pattern, and how modest changes to a particular component orientation (e.g., backbone or side-chain tilt) influence the diffraction pattern. The effects on the polymer crystal structure of varying the alkyl side-chain length from C(12) to C(14) and C(16) are also studied. The accurate determination of the three-dimensional polymer structure allows us to examine the PBTTT electronic band structure and intermolecular electronic couplings (transfer integrals) as a function of alkyl side-chain length. This combination of theoretical and experimental techniques proves to be an important tool to help establish the relationship between the structural and electronic properties of polymer thin films.