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The Behavioral Inhibition Questionnaire-Short Form (BIQ-SF) is a 14-item parent-rating scale for assessing an inhibited, anxiety-prone temperament in preschool children. This study examined the psychometric properties of the BIQ-SF scores in a multi-ethnic community population of Dutch boys and girls aged 2.5-6 years (total N = 2,343, from which various subsamples were derived). Results revealed that the factor structure of the BIQ-SF was as hypothesized: a model with six correlated factors representing children's inhibited behaviors in various social and non-social contexts provided a good fit for the data. The internal consistency of the BIQ-SF was generally satisfactory and scores on the scale were found to be fairly stable over a time period of up to 2 years. Parent-teacher agreement was acceptable, and relations between the BIQ-SF and observations of an inhibited temperament were moderate. Finally, BIQ-SF scores were positively associated with measures of anxiety and internalizing symptoms, whereas no significant links were found with externalizing symptoms. Altogether, these results provide support for the reliability and validity of the BIQ-SF as an economical method for assessing behavioral inhibition and anxiety proneness in young children.

Polar metal–organic frameworks have potential applications as functional non-linear optical, piezoelectric, pyroelectric and ferroelectric materials. Using second harmonic generation microscopy we found that fluoride doping of the microporous iron(III) terephthalate MOF MIL-53(Fe) induces a polar organization in its structure, which was not previously detected with XRD. The polar order is only observed when both fluoride and guest molecules are present, and may be related to a complex interplay between the adsorbates and the framework, leading to a modification of the positioning of fluoride in the inorganic Fe-chains. Combined polarized second harmonic generation microscopy and scanning pyroelectric microscopy show that the polar axis is unidirectional and of the same sense over the whole crystal, extending up to 100 micrometers. This finding shows how MOF materials can be endowed with useful properties by doping MOFs with fluoride. crosscheck: This document is CrossCheck deposited related_data: Supplementary Information identifier: Karen Markey (ORCID) copyright_licence: The Royal Society of Chemistry has an exclusive publication licence for this journal copyright_licence: This article is freely available. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence (CC BY 3.0) history: Received 26 November 2015; Accepted 18 January 2016; Accepted Manuscript published 18 January 2016; Advance Article published 26 January 2016; Version of Record published 1 March 2016 ispartof: Dalton Transactions vol:45 issue:10 pages:4401-4406 ispartof: location:England status: published

Objectives The aim of this cross-sectional study was to assess the correlation between dental plaque scores determined by the measurement of red autofluorescence or by visualization with a two-tone solution. Clinical photographs were used for this study. Materials and methods Overnight plaque from the anterior teeth of 48 participants was assessed for red fluorescence on photographs (taken with a QLF-camera) using a modified Quigley & Hein (mQH) index. A two-tone disclosing solution was applied. Total disclosed plaque was clinically assessed using the mQH index. In addition, total and blue disclosed plaque was scored on clinical photographs using the mQH index. Results A strong correlation was observed between the total disclosed plaque scored on photographs and the clinical scores (r = 0.70 at site level; r = 0.88 at subject level). The correlation between red fluorescent plaque and total plaque, as assessed on the photographs, was moderate to strong and significant (r = 0.50 at the site level; r = 0.70 at the subject level), with the total plaque scores consistently higher than the red fluorescent plaque scores. The correlation between red fluorescent plaque and blue disclosed plaque was weak to moderate and significant (r = 0.30 at the site level; r = 0.50 at the subject level). Conclusions Plaque, as scored on white-light photographs, corresponds well with clinically assessed plaque. A weak to moderate correlation between red fluorescing plaque and total disclosed plaque or blue disclosed plaque was found. Clinical relevance What at present is considered to be matured dental plaque, which appears blue following the application of a two-tone disclosing solution, is not in agreement with red fluorescent dental plaque assessment.

Background : Some dental plaque fluoresces red. The factors involved in this fluorescence are yet unknown. Objective : The aim of this study was to assess systematically the effect of age, thickness, and cariogenicity on the extent of red fluorescence produced by in vitro microcosm biofilms. Design : The effects of biofilm age and thickness on red fluorescence were tested in a constant depth film fermentor (CDFF) by growing biofilms of variable thicknesses that received a constant supply of defined mucin medium (DMM) and eight pulses of sucrose/day. The influence of cariogenicity on red fluorescence was tested by growing biofilm on dentin disks receiving DMM, supplemented with three or eight pulses of sucrose/day. The biofilms were analyzed at different time points after inoculation, up to 24 days. Emission spectra were measured using a fluorescence spectrophotometer (λ exc 405 nm) and the biofilms were photographed with a fluorescence camera. The composition of the biofilms was assessed using 454-pyrosequecing of the 16S rDNA gene. Results : From day 7 onward, the biofilms emitted increasing intensities of red fluorescence as evidenced by the combined red fluorescence peaks. The red fluorescence intensity correlated with biofilm thickness but not in a linear way. Biofilm fluorescence also correlated with the imposed cariogenicity, evidenced by the induced dentin mineral loss. Increasing the biofilm age or increasing the sucrose pulsing frequency led to a shift in the microbial composition. These shifts in composition were accompanied by an increase in red fluorescence. Conclusions : The current study shows that a thicker, older, or more cariogenic biofilm results in a higher intensity of red fluorescence. Keywords: dental plaque; fluorescence; microbiology; biofilms; microbiota; microcosm (Published: 7 April 2016) Citation: Journal of Oral Microbiology 2016, 8: 30346 - http://dx.doi.org/10.3402/jom.v8.30346

Ferroelectric metal–organic frameworks are emerging as an exciting field of research and have witnessed great progress in the last decade. In this contribution, we briefly discuss ferroelectricity and its means of demonstration. Three mechanisms that lead to ferroelectricity are identified and critically discussed. On the basis of the shortcomings present in the literature, we present a protocol for the study of ferroelectricity in MOF compounds.

The aim of this investigation was to use quantitative light-induced fluorescence to study the natural behavior of white-spot lesions that developed in orthodontic patients during treatment with fixed orthodontic appliances, after the removal of those appliances.The sample comprised 58 consecutively recruited patients who were at least 12 years old and who had been treated with a fixed appliance for at least 1 year in the department of orthodontics at the Academic Center for Dentistry Amsterdam, The Netherlands. They were examined with quantitative light-induced fluorescence for the presence and the extent of caries on the buccal surfaces of their teeth directly after debonding and 6 weeks and 6 months later. The fluorescence loss (DeltaF [%]) and area of lesions (mm2) were determined for all lesions found.A total of 421 carious lesions were recorded at debracketing with an average fluorescence loss (DeltaF(0)) of 10.3% (SD, 5.4%). During the study, 15 lesions were lost from quantitative light-induced fluorescence analysis: 11 lesions (DeltaF(MAX,0)25%) in 2 subjects were restored, and 4 were not analyzed because they were not imaged properly. Lesions varied from incipient, ie, white spot (DeltaF(0)10%, n = 257), to advanced, ie, dentinal (DeltaF(0)25%, n = 12). A small lesion improvement was seen 6 weeks after debracketing (P.01), and a further lesion improvement was seen after 6 months (P.01). Incipient lesions on average showed a smaller improvement (relative decrease, 2%; SD, 20%) than lesions with DeltaF(0)10% (relative decrease, 12%; SD, 20%; P.01).The lesions that developed during orthodontic treatment improved once the fixed appliances were removed even when they were advanced, but the overall regression was small.

Recently, MIL-125(Ti) and NH2 -MIL-125(Ti), two titanium-based metal-organic frameworks, have attracted significant research attention in the field of photocatalysis for solar fuel generation. This work reveals that the differences between these structures are not only based on their light absorption range but also on the decay profile and topography of their excited states. In contrast to MIL-125(Ti), NH2 -MIL-125(Ti) shows markedly longer lifetimes of the charge-separated state, which improves photoconversion by the suppression of competing decay mechanisms. We used spectroelectrochemistry and ultrafast spectroscopy to demonstrate that upon photoexcitation in NH2 -MIL-125(Ti) the electron is located in the Ti-oxo clusters and the hole resides on the aminoterephthalate unit, specifically on the amino group. The results highlight the role of the amino group in NH2 -MIL-125(Ti), the electron donation of which extends the lifetime of the photoexcited state substantially.

Interpenetration, the entwining of multiple lattices, is a common phenomenon in metal-organic frameworks (MOFs). Typically, in interpenetrated MOFs the sub-lattices are fully occupied. Here we report a family of MOFs in which one sub-lattice is fully occupied and the occupancy level of the other can be controlled during synthesis to produce frameworks with variable levels of partial interpenetration. We also report an 'autocatenation' process, a transformation of non-interpenetrated lattices into doubly interpenetrated frameworks via progressively higher degrees of interpenetration that involves no external reagents. Autocatenation maintains crystallinity and can be triggered either thermally or by shear forces. The ligand used to construct these MOFs is chiral, and both racemic and enantiopure partially interpenetrated frameworks can be accessed. X-ray diffraction, nonlinear optical microscopy and theoretical calculations offer insights into the structures and dynamic behaviour of these materials and the growth mechanisms of interpenetrated MOFs. ispartof: Nature Chemistry vol:8 issue:3 pages:250-257 ispartof: location:England status: published

A sensitive, quantitative method for investigating changes in enamel mineralization of specimens subjected to in vitro or in situ experimentation is presented. The fluorescence-detecting instrument integrates a Xenon arc light source and an object positioning stage, which makes it particularly suitable for the nondestructive assessment of demineralized or remineralized enamel. We demonstrate the ability of in vitro quantitative light-induced fluorescence (QLF) to quantify changes in mineralization of bovine enamel discs that had been exposed in vitro to a demineralizing gel (n=36) or biofilm-mediated demineralization challenges (n=10), or were carried in situ by three volunteers during a 10-day experiment (n=12). Further experiments show the technique's value for monitoring the extent of remineralization in 36 specimens exposed in vitro to oral multispecies biofilms and document the repeatability of in vitro QLF measurements (n=10) under standardized assay conditions. The validity of the method is illustrated by comparison with transversal microradiography (TMR), the invasive current gold standard for assessing experimental changes in enamel mineralization. Ten discs with 22 measurement areas for comparison demonstrated a positive correlation between TMR and QLF (r=0.82). Filling a technological gap, this QLF system is a promising tool to assay in vitro nondestructively localized changes in mineralization of enamel specimens.

© The Royal Society of Chemistry 2015. We describe a nonlinear optical study of gold triangles that exploits a higher order plasmonic resonance. A comprehensive nonlinear optical characterisation was performed both by second harmonic generation (SHG) and two photon fluorescence spectroscopy (2PF). We demonstrate and explain the enhancement of the coherent and incoherent nonlinear optical emission by a higher order multipolar mode of the plasmonic structure. The peculiarities of the mode shape and its influence on intensity and polarisation of the nonlinear signal are experimentally and numerically confirmed. crosscheck: This document is CrossCheck deposited related_data: Supplementary Information copyright_licence: The Royal Society of Chemistry has an exclusive publication licence for this journal copyright_licence: The accepted version of this article will be made freely available after a 12 month embargo period history: Received 24 October 2014; Accepted 10 December 2014; Advance Article published 7 January 2015; Version of Record published 5 February 2015 ispartof: Journal of Materials Chemistry C vol:3 issue:7 pages:1576-1581 status: published

BackgroundProviding safety education to parents of young children is important in the prevention of unintentional injuries in or around the home. We developed a Web-based, tailored safety advice module to support face-to-face counseling in the setting of preventive youth health care (E-health4Uth home safety) in order to improve the provision of safety information for parents of young children. ObjectiveThis pilot study evaluated a Web-based, tailored safety advice module (E-health4Uth home safety) and evaluated the use of E-health4Uth home safety to support counseling in routine well-child care visits. MethodsFrom a preventive youth health care center, 312 parents with a child aged 10-31 months were assigned to the E-health4Uth home safety condition or to the care-as-usual condition (provision of a generic safety information leaflet). All parents completed a questionnaire either via the Internet or paper-and-pencil, and parents in the E-health4Uth condition received tailored home safety advice either online or by a print that was mailed to their home. This tailored home safety advice was used to discuss the safety of their home during the next scheduled well-child visit. Parents in the care-as-usual condition received a generic safety information leaflet during the well-child visit. ResultsMean age of the parents was 32.5 years (SD 5.4), 87.8% (274/312) of participants were mothers; mean age of the children was 16.9 months (SD 5.1). In the E-health4Uth condition, 38.4% (61/159) completed the online version of the questionnaire (allowing Web-based tailored safety advice), 61.6% (98/159) preferred to complete the questionnaire via paper (allowing only a hardcopy of the advice to be sent by regular mail). Parents in the E-health4Uth condition evaluated the Web-based, tailored safety advice (n=61) as easy to use (mean 4.5, SD 0.7), pleasant (mean 4.0, SD 0.9), reliable (mean 4.6, SD 0.6), understandable (mean 4.6, SD 0.5), relevant (mean 4.2, SD 0.9), and useful (mean 4.3, SD 0.8). After the well-child visit, no significant differences were found between the E-health4Uth condition and care-as-usual condition with regard to the satisfaction with the information received (n=61, P=.51). Health care professionals (n=43) rated the tailored safety advice as adequate (mean 4.0, SD 0.4) and useful (mean 3.9, SD 0.4). ConclusionsLess than half of the parents accepted the invitation to complete a Web-based questionnaire to receive online tailored safety advice prior to a face-to-face consultation. Despite wide access to the Internet, most parents preferred to complete questionnaires using paper-and-pencil. In the subgroup that completed E-health4Uth home safety online, evaluations of E-health4Uth home safety were positive. However, satisfaction scores with regard to tailored safety advice were not different from those with regard to generic safety information leaflets.

Chemistry of materials 25, 17-26 (2013). doi:10.1021/cm3025445, Published by American Chemical Society, Washington, DC

Since the discovery of graphene in 2004 by Novoselov and Geim, a lot of research emphasis has been directed towards its characterization. Most of the important scientific breakthroughs have been obtained on exfoliated graphene (produced via the well known 'scotch tape' method), nowadays, different synthetic routes have been developed to obtain largescale graphene. Among several optical techniques, Raman spectroscopy is the one most often employed to characterize the defects, number of graphene layers and other properties of the graphitic films regardless of their fabrication method. In this work, we will report on the microscopic imaging of the two-photon fluorescence (2PF) properties and the secondharmonic generation (SHG) in both single layer and few layer graphene. © 2012 SPIE. ispartof: pages:8474-1 ispartof: Proceedings of SPIE vol:8474 pages:8474-1 ispartof: Optical Processes in Organic Materials and Nanostructures location:San Diego, California, USA date:12 Aug - 12 Aug 2012 status: published

We present a methodology based on polarization-controlled second-harmonic generation microscopy that allows one to determine the point group symmetry of noncentrosymmetric structures in situ and in vivo in complex systems regardless of the occurrence of periodicity. Small, randomly oriented structures suffice for the analysis, which is based on simple recognition of observables in four tests. These can be performed in any standard SHG-microscope that allows polarization control of the incident and detected light. The method is resilient to birefringence and light dispersion.

The porous MIL-47 material shows a selective adsorption behavior for para-, ortho-, and meta-isomers of xylenes, making the material a serious candidate for separation applications. The origin of the selectivity lies in the differences in interactions (energetic) and confining (entropic). This paper investigates the xylene-framework interactions and the xylene-xylene interactions with quantum mechanical calculations, using a dispersion-corrected density functional and periodic boundary conditions to describe the crystal. First, the strength and geometrical characteristics of the optimal xylene-xylene interactions are quantified by studying the pure and mixed pairs in gas phase. An extended set of initial structures is created and optimized to sample as many relative orientations and distances as possible. Next, the pairs are brought in the pores of MIL-47. The interaction with the terephthalic linkers and other xylenes increases the stacking energy in gas phase (-31.7 kJ/mol per pair) by roughly a factor four in the fully loaded state (-58.3 kJ/mol per xylene). Our decomposition of the adsorption energy shows various trends in the contributing xylene-xylene interactions. The absence of a significant difference in energetics between the isomers indicates that entropic effects must be mainly responsible for the separation behavior.

In the quest for organic second-order nonlinear materials, self-assembled structures based on octupolar molecules have shown to be promising candidates. The presented work focuses on an octupolar substituted 1,3,5-trisalkynylbenzene that forms crystals that show significant second-harmonic generation (SHG). Continuous polarization SHG measurements were performed to elucidate the tensorial nature of this response. Unfortunately the model at hand was unable to fit the polarization patterns due to depolarization of the second harmonic beam caused by multiple scattering in the sample. Although the chromophore is clearly achiral, these patterns revealed a different response for left and right circularly polarized light, also known as SHG circular difference. This implies that these molecules spontaneously assemble in chiral superstructures. These surprising results were confirmed by circular dichroism spectroscopy, revealing a monosignate CD band that must be attributed to a supramolecular chiral organization.

Orthodontic treatment with fixed appliances is considered a risk factor for the development of white spot caries lesions (WSL). Traditionally, brackets are bonded to the buccal surfaces. Lingual brackets are developing rapidly and have become more readily available. Buccal surfaces are considered to be more caries prone than lingual surfaces. Furthermore, lingual brackets are shaped to fit the morphology of the teeth and seal almost the entire surface. In the present study we tested the hypothesis that lingual brackets result in a lower caries incidence than buccal brackets. We tested this hypothesis using a split-mouth design where subjects were allocated randomly to a group receiving either buccal or lingual brackets on the maxillary teeth and the alternative bracket type in the mandible. The results indicate that buccal surfaces are more prone to WSL development, especially when WSL existed before treatment. The number of WSL that developed or progressed on buccal surfaces was 4.8 times higher than the number of WSL that developed or progressed on lingual surfaces. When measured using quantitative light-induced fluorescence (QLF), the increase in integrated fluorescence loss was 10.6 times higher buccally than lingually. We conclude that lingual brackets make a difference when caries lesion incidence is concerned.

Knowledge of the diffusion of chemicals through buried films is important for a wide variety of systems--from sensing to drug delivery. Herein, we show that second-harmonic generation (SHG) can be used to follow the diffusion through a thin film buried under a liquid in situ. More specifically, the diffusion of 4-(4-diethylaminostyryl)-1-methylpyridinium iodide through zeolite precursor films of different thickness is followed. The diffusion coefficients are calculated according to Fick's law.

Three metal-organic frameworks (MOFs) with similar pore window diameters, [Cu(3)(BTC)(2)], MIL-47 and MIL-53(Al), are tested for adsorption of olefins, alkylnaphthalenes and dichlorobenzenes in the liquid phase. Selective adsorption of olefins is possible only on [Cu(3)(BTC)(2)] viapi-complexation on its open metal sites. This material shows a remarkable preference for cis-olefins over trans-olefins. All three MOFs have high affinities for alkylnaphthalene and dichlorobenzene isomers. Separation of 1,4-dimethylnaphthalene from other alkylnaphthalene isomers and of p- and m-dichlorobenzene can be carried out on both MIL-47 and MIL-53(Al), as shown with breakthrough experiments. For the alkylnaphthalenes, column experiments at different concentrations point to enthalpic interactions as important factors determining selectivity, and the occurrence of steric effects during the adsorption of 1,4-dimethylnaphthalene shows that its kinetic diameter approaches the pore diameter of the adsorbents. For the dichlorobenzenes, packing effects dominate the adsorption selectivity.

The inherently surface-specific technique of second-harmonic generation was employed to probe the adsorption of an organic molecule, a hemicyanine dye, on b-oriented silicalite-1 films in situ. Measurements were performed in a purpose-built cell for solution experiments. By measuring at two different polarization combinations of the fundamental and second-harmonic light, the orientation of the adsorbed molecules was measured continuously. It has been observed that the adsorbed molecules gradually align themselves with the straight pores of the zeolite crystallites, thus adsorbing into the pores.

Diagnostic methods for the use in preventive dentistry are being developed continuously. Few of these find their way into general practice. Although the general trend in medicine is to focus on disease prevention and early diagnostics, in dentistry this is still not the case. Nevertheless, in dental research some of these methods seem to be promising for near future use by the general dental professional. In this paper an overview is given of a method called quantitative light-induced fluorescence or (QLF) in which visible and harmless light excites the teeth in the patient's mouth to produce fluorescent images, which can be stored on disk and computer analyzed. White spots (early dental caries) are detected and quantified as well as bacterial metabolites on and in the teeth. An overview of research to validate the technique and modeling to further the understanding of the technique by Monte Carlo simulation is given and it is shown that the fluorescence phenomena can be described by the simulation model in a qualitative way. A model describing the visibility of red fluorescence from within the dental tissue is added, as this was still lacking in current literature. An overview is given of the clinical images made with the system and of the extensive research which has been done. The QLF™ technology has been shown to be of importance when used in clinical trials with respect to the testing of toothpastes and preventive treatments. It is expected that the QLF™ technology will soon find its way into the general dental practice.

no abstract available ispartof: Angewandte Chemie (International ed.) vol:46 issue:23 pages:4293-4297 ispartof: location:Germany status: published

A basic understanding of the light-scattering processes that take place inside the dental tissue (either sound or carious) is obtained both with measurements of the photon path-length distribution of light inside such media and with Monte Carlo simulations. Furthermore, the following is investigated: the correlations between different moments of the photon path-length distribution of light inside caries lesions, the fluorescence loss determined with quantitative light-induced fluorescence, and/or the demineralization and depth of caries lesions determined with transversal microradiography. It is concluded that (i) the light paths inside both carious and sound enamel are considerably influenced by the refractive-index contrast at the tooth surface; (ii) contrary to a previous hypothesis, the fluorescence loss is larger in lesions in which the average photon path length is longer; (iii) very good correlations are obtained between the optical characteristics and the physical parameters of lesions when the optical measurements are performed such that there is high refractive contrast at the tooth surface. (C) 2003 Optical Society of America.

Quantitative light-induced fluorescence (QLF) is based on the dark appearance of a white spot in otherwise highly fluorescent enamel. This can be explained by the increased scattering coefficient in the white spot compared with that of sound enamel. The aim of this study was to estimate the effect of different sound enamel scattering coefficients (sSE) and enamel thickness d, caused by developmental enamel differences, on the fluorescence appearance of white-spot lesions. We ran a Monte Carlo simulation of a 4 × 4 mm2 illuminated enamel slab on a highly fluorescent background. The slab had a 0.7 × 0.7 mm2, 100-µm-deep, white spot in the center. Fluorescent and back-scattered photons re-emitted from the central 2 × 2 mm2 were recorded. We found that the fluorescence photon excitance from the white spot (FWS) was less than that of sound enamel (FSE), with an optimum difference for SSE between 20 and 80/mm. For sSE SE and FWS decreased with d. We found no relation with d for sSE >20/mm. The results indicate that for small sSE, we are suffering from edge losses, which explains why the optimum for lesion visibility is not found at sSE = 0/mm, as would be expected.

For the first time, second-harmonic generation microscopy (SHGM) has been employed to study zeolites. Large ZSM-5 crystals filled with p-nitroaniline (PNA) dipoles have been visualized. It is shown that SHGM can discriminate between the straight b-pores and the sinusoidal a-pores of this zeolite, thus revealing the intergrown structure of these crystals. Moreover, it is shown that dipole chains are formed not only in the b-pores but also in the a-pores. PNA only assembles into dipole chains of parallel orientation in those pores that are directly accessible from the outer surface. The area in which this PNA ordering prevails is limited to a strip near the outer surface of the zeolite crystal. A rationalization for these two observations is offered.

The aim of this paper is to report on the demineralization-induced changes in dentin autofluorescence. Confocal laser scanning microscopy (CLSM) images and fluorescence excitation and emission spectra of in vitro demineralized root surfaces and sound controls on the same tooth roots were compared. When observed in CLSM images, demineralized dentin, excited at 488 nm, gave an increased emission at 529 nm compared to sound dentin. The difference in fluorescence decreased deeper into the root, as the sound dentin underneath the lesion was reached. In contrast, when using fluorescence spectrophotometry, excitation around 460 and 488 nm yielded a lower emission around 520 nm for demineralized dentin than for sound dentin, but in a more pronounced peak. From excitation spectra for emission around 520 nm, it could be seen that in demineralized dentin the contribution of excitation between 480 and 520 nm was more important than in sound dentin. The recorded fluorescence in CLSM images was not affected by demineralization-caused changes in scattering and absorption properties, due to the small measurement volume. Thus, the increased fluorescence for demineralized dentin implies an increased quantum yield. In fluorescence spectrophotometry, where the measurement volume is large, changes in scattering and absorption do have an influence on the fluorescence signal. Then, increased absorption by non-fluorescing chromophores and increased re-absorption around the emission wavelength may compensate for the increase in quantum yield and absorption around the excitation wavelength by fluorophores.

Second-harmonic generation microscopy (SHGM) has been employed to study crystals of zeolite-like material SAPO-5 filled with p-nitroaniline (PNA). The SHG and 2-photon fluorescence response of PNA in the one-dimensional channels readily reveals the pore accessibility; intergrown crystallites containing hexagonal pyramidal components and internal diffusion barriers are found next to seemingly perfect crystals. The sensitivity of second-harmonic generation to molecular orientation allowed for mapping of the domains of differently organized PNA. Dense domains of highly aligned PNA alternate with dilute zones with loosely aligned PNA.

Metal-organic frameworks (MOFs) are a class of nanoporous crystalline materials with very high structural tunability. They possess a very low dielectric permittivity ϵr due to their porosity and hence are favorable for piezoelectric energy harvesting. Even though they have huge potential as piezoelectric materials, a detailed analysis and structure-property relationship of the piezoelectric properties in MOFs are lacking so far. This work focuses on a class of cubic non-centrosymmetric MOFs, namely, zeolitic imidazolate frameworks (ZIFs) to rationalize how the variation of different building blocks of the structure, that is, metal node and linker substituents affect the piezoelectric constants. The piezoelectric tensor for the ZIFs is computed from ab initio theoretical methods. From the calculations, we analyze the different contributions to the final piezoelectric constant d14, namely, the clamped ion (e140) and the internal strain (e14int) contributions and the mechanical properties. For the studied ZIFs, even though e14 (e140 + e14int) is similar for all ZIFs, the resultant piezoelectric coefficient d14 calculated from piezoelectric constant e14 and elastic compliance constant s44 varies significantly among the different structures. It is the largest for CdIF-1 (Cd2+ and -CH3 linker substituent). This is mainly due to the higher elasticity or flexibility of the framework. Interestingly, the magnitude of d14 for CdIF-1 is higher than II-VI inorganic piezoelectrics and of a similar magnitude as the quintessential piezoelectric polymer polyvinylidene fluoride.