Influence Of Molecular Packing Research Articles

Influence of molecular packing on the color-tunable emissive behavior of viologen derivatives

Color-tunable organic solid-state luminescent materials have received increasing attention owing to their potential applications in displays, imaging, encryption, etc. To provide more information about structure-packing-property relationship of color-tunable organic luminophores, molecules with definite structures and explicit molecular packing are highly desired. In this work, we present an strategy to realize color-tunable luminescence by using the organic molecule 1-(4-carboxyphenyl)-4,4′-bipyridinium (CPB) as building block to construct two kinds of polymorphs by altering molecular conformation and packing modes. The color-tunable emission and relationship between the molecular packing fashion and bulk optical properties are reported. The findings open the opportunity for the development of novel color-tunable luminophores.

Simultaneous access to the low-frequency dynamics and ultraslow kinetics of the thermal expansion behavior of polyurethanes

A long-lasting technological and scientific need exists for more detailed understanding of the dynamics of thermo-mechanical properties of polymers. This article demonstrates how low-frequency dynamics and ultraslow kinetics of thermal expansion of polymers are easily measured by the spectroscopic dilatometry technique called “Temperature Modulated Optical Refractometry”. The influence of molecular packing and dynamics is investigated on the kinetic and dynamic glass transition of three visco-elastic polyurethane networks of different crosslink density. A major observation is the potentially massive difference between kinetic and dynamic thermal expansion coefficients for the vitrifying polyurethane networks at a given temperature. The same holds true for the kinetic and dynamic glass transition temperatures Tg kin and Tg dyn, which are observed to differ by 15 K under given cooling and temperature modulation conditions. The here used cooling procedures show how in general the comparison of the low-frequency dynamics with the kinetics allows for a given material to estimate the dynamic response from the kinetic response, and vice versa. First insights are gained into how far the relaxation dynamics of the polyurethane networks spread over a considerably larger temperature interval than those of a linear chain polymer.

The Influence of Molecular Packing on the Emissive Behavior of Pyrene Derivatives: Mechanoluminescence and Mechanochromism

AbstractAlthough some bright, organic mechanoluminescence (ML) luminogens with aggregation‐induced emission properties and twisted molecular structures are recently reported, those with planar structures and bright ML and their related effective design strategies are not yet explored, partially due to aggregation‐caused quenching in luminogens with planar structures. Herein, using the unique solid‐state packing style of pyrene, bright dual monomer‐excimer‐ML and excimer‐ML from two pyrene derivatives (Py‐Bpin and Py‐Br) with a simple, planar molecular structure are reported for the first time, and two analogs of pyrene and Py‐H are used for comparison. These four luminogens display similar optical properties in dilute solution but different luminescent properties in the solid state, mainly due to their different molecular packing. Interestingly, pyrene is mechanochromism (MC)‐ and ML‐inactive, while Py‐H is MC‐active, Py‐Bpin is MC‐ and ML‐active, and Py‐Br is ML‐active. The relationship between molecular packing and ML/MC properties is confirmed by analyzing single‐crystal structures and related experimental results, providing important information to further understand the mysterious ML process and opening a new way to design efficient luminogens with both MC and ML.

Expanded Theory of H- and J-Molecular Aggregates: The Effects of Vibronic Coupling and Intermolecular Charge Transfer.

The electronic excited states of molecular aggregates and their photophysical signatures have long fascinated spectroscopists and theoreticians alike since the advent of Frenkel exciton theory almost 90 years ago. The influence of molecular packing on basic optical probes like absorption and photoluminescence was originally worked out by Kasha for aggregates dominated by Coulombic intermolecular interactions, eventually leading to the classification of J- and H-aggregates. This review outlines advances made in understanding the relationship between aggregate structure and photophysics when vibronic coupling and intermolecular charge transfer are incorporated. An assortment of packing geometries is considered from the humble molecular dimer to more exotic structures including linear and bent aggregates, two-dimensional herringbone and "HJ" aggregates, and chiral aggregates. The interplay between long-range Coulomb coupling and short-range charge-transfer-mediated coupling strongly depends on the aggregate architecture leading to a wide array of photophysical behaviors.

Nanoscale Conductance in Lead Phthalocyanine Thin Films: Influence of Molecular Packing and Humidity

The influence of crystalline phase and disorder on vertical charge transport in nonplanar metallophthalocyanines is studied by depositing thin films of shuttlecock molecules, lead phthalocyanine (PbPc), and SnPc on various substrates such as highly oriented pyrolytic graphite (HOPG), silicon, and gold and investigating the structural and electrical characteristics of the films. The films represent three cases of crystalline packing such as monoclinic, triclinic, and disordered phases, directed by the substrate–molecule interactions and intermolecular interactions. Theoretical calculations are performed to understand the molecular orientations on the substrate and give insights into the possible origin of ordered and disordered packing. Vertical charge transport in the films is studied by employing conducting atomic force microscopy and compared with bulk electrical measurements. It is revealed that the monoclinic phase of PbPc on HOPG exhibits two orders of magnitude higher conductance than silicon or gol...

Benzotrithiophene Copolymers: Influence of Molecular Packing and Energy Levels on Charge Carrier Mobility

The planar benzotrithiophene unit (BTT) was incorporated into four different donor polymers, and by systematically changing the nature and positioning of the solubilizing alkyl side chains along the conjugated backbone, the polymers’ frontier energy levels and optoelectronic properties were controlled. Reducing the steric hindrance along the polymer backbone lead to strong interchain aggregation and highly ordered thin films, achieving hole mobilities of 0.04 cm2/(V s) in organic thin film transistors. In an attempt to increase the polymer’s processability and reduce chain aggregation, steric hindrance between alkyl side chains was exploited. As a result of the increased solubility, the film forming properties of the polymer could be improved, but at the cost of reduced hole mobilities in OFET devices, due to the lack of long-range order in the polymer films.

Influence of molecular packing on the corrosion inhibition properties of self-assembled octadecyltrichlorosilane monolayers on silicon

The corrosion inhibition properties of octadecyltrichlorosilane (OTS) self-assembled monolayers (SAMs) on silicon were investigated. Atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), contact angle (CA), and lateral force microscopy (LFM) were used to determine the OTS film formation time, packing density, and corrosion protection efficacy. The OTS films reached adsorption saturation after 15s; however, the molecular density continued to increase up to 24h. The films were exposed to the strong oxidant KMnO4, and while 15-s film samples exhibited corrosion after a 1min exposure, samples with films grown for 24h were protected even after 24h.

Investigation of hydrogen bond effects on the hyperpolarizability of 2-Aminopyridinium maleate (2APM) complex and determining the non-linear optical susceptibility of the molecular crystal of 2APM

2-Aminopyridinium maleate (2APM) is a recently discovered organic acid-base complex that crystallizes in a non-centrosymmetric space group Pc and hence has a nonzero second-order optical susceptibility. In 2APM the cation (aminopyridinium ion) is connected to the anion (maleate ion) through hydrogen bonds (N1-H10–O2 and N2-H12–O1), we have calculated the molecular properties of 2APM for varying strength of these hydrogen bonds. It is observed that the molecular hyperpolarizabilty varies for varying strength of these hydrogen bonds. These observations are interpreted in terms of the change in nature of the hydrogen bond interaction as its strength is varied. Macropscopic second-order optical susceptibility (d 0) of 2APM is obtained using the calculated value of molecular hyperpolarizability and the reported crystal structure of 2APM. In order to study the influence of molecular packing on the macroscopic non-linear optical property of the crystal, susceptibility calculations are repeated for 2-methyl-4nitroaniline (MNA) crystal, which is a very well known non-linear optical organic crystal with an exceptionally high value of second-order optical susceptibility. A comparison between the non-linear optical property of 2APM and MNA crystals is given. Comparing the values of d 0 of 2APM crystals with that of urea shows that the nonlinear optical response of 2APM crystals will be nearly 10 times that of a urea crystal.

Two-dimensional proton conduction at a membrane surface: Influence of molecular packing and hydrogen bonding

Evidence for two-dimensional protonic charge transport along a monolayer/water interface is presented, supporting the concept of localised charge transport along membrane surface. Charge transport proceeds only at and above a critical molecular packing density, and probably occurs via a network of hydrogen-bonded water molecules and lipid headgroups.