Modelling the effect of nonplanarity on charge transport along conjugated polymer chains

Conjugated polymers show interesting properties that make them appropriated for nanoelectronics. Several studies of poly(p-phenylene vinylene) (PPV) have suggested that each polymer chain consists of several planar segments, with conjugation length of nanoscale dimension, linked by twists or kinks. A pronounced twist between two planar segments in a PPV chain not only causes loss of main-chain conjugation but it may also alter electron and hole mobility along the chain, which has further implications for the percolation of charge through the polymer film. We used self-consistent quantum molecular dynamics calculations to provide information on the electric field needed to move the injected charges (either electrons or holes) along the planar segments of PPV and to cross the twist between two planar segments perpendicular to each other. Field-dependent charge mobility was also estimated for conjugated segments of various lengths. Our results suggest that electrons can cross the twist between adjacent planar segments for lower applied electric fields than holes if there is no more than one electronic charge (electron or hole) on the PPV chain, otherwise similar fields are needed.Fundação para a Ciência e a Tecnologia FCT) Programa Operacional “Ciência , Tecnologia, Inovação” – POCTI/CTM/41574/2001, CONC-REEQ/443/EEI/2001 e SFRH/BD/11231/200

Mesoscopic modelling of bipolar charge evolution in CN-PPV LEDs

Since various chances are possible in the molecular structure of the repeat unit, substituted poly(para-phenylenevinylene) (PPV) has ben used as active component in light-emitting diodes (LEDs) to obtain light emission in a wide range of colours.A major aspect determining device performance is the competition between current flow, trapping and recombination within the polymer layer. By suitable Monte Carlo calculations, we have performed computer experiments in which bipolar charge carriers are injected at constant rate in polymer networks made of cyano-substituted PPV chains with variable length and orientation. The intra-molecular electronic properties used in these simulations were calculated by a quantum molecular dynamics method. In order to assess the influence of cyano-substitution on the properties of single-layer PPV LEDs, we have focused our attention on bipolar charge evolution in time. Specifically addressed are the differences in electric field strength needed for intra-molecular charge mobility of electrons and holes and their consequences at mesoscopic scale. (C) 2004 Elsevier B.V. All rights reserved

Computer simulation of electron transfer in molecular electronic devices

The study of electron transfer through individual molecules bound to metal electrodes has become important due to the potential application in molecular electronic devices. Since the electronic and atomic motions in these molecules influence each other they need to be treated self-consistently. We have used self-consistent quantum chemistry molecular dynamics calculations to discuss some of the issues related to electron transfer through a spatially symmetric [9,10-Bis((2′-para-mercaptophenyl)-ethinyl)-anthracene] and an asymmetric [1,4-Bis((2′-para-mercaptophenyl)-ethinyl)-2-acetyl-amino-5-nitro-benzene] molecule bound to metal electrodes. Specifically addressed are the effects of voltage inversion on electron transfer between electrodes through both molecules. Our results show an electron transfer behaviour that reproduces the spatial symmetry of the molecules in agreement with experimental current-voltage data. The change in time of electron density and dimerisation at specific atomic sites is also discussed.Fundação para a Ciência e a Tecnologia (FCT) - Programa Operacional “Ciência , Tecnologia, Inovação” - POCTI/CTM/41574/2001, SFRH/BD/11231/2002.Comunidade Europeia (CE). Fundo Europeu de Desenvolvimento Regional (FEDER)

Intra-molecular properties of DMeOPPV studied by quantum molecular dynamics

Introducing methoxy electron donor groups into a poly(para-phenylene vinylene) (PPV) chain will lead to the appearance of unique electronic properties at the molecular scale which should affect the overall properties of light-emitting diodes based on these polymers. Self-consistent quantum molecular dynamics calculations have been used to provide information on intra-molecular properties of poly(2,5-dimethoxy-para-phenylene vinylene) (DMeOPPV), which are relevant for the modelling and characterization of polymer light-emitting diodes at nanometric length scale. We focus our attention on those properties that have been somewhat neglected in previous literature: the charge distribution associated with positive and negative charge carriers and their intra-molecular mobility when an electric field is applied.Fundação para a Ciência e a Tecnologia (FCT) – Programa Operacional “Ciência, Tecnologia, Inovação” - POCTI/CTM/41574/2001, SFRH/BD/11231/2002.Comunidade Europeia (CE). Fundo Europeu de Desenvolvimento Regional (FEDER

Modelling the effect of non-planarity on luminescence energy of conjugated polymers

We present theoretical investigations of structural and electronic properties of ground-state and low-lying excited singlet states in isolated chains of conjugated polymers using a self-consistent quantum molecular dynamics method. With this approach, we have determined the energy of both states as function of the twist angle between two planar segments of the same polymer chain, for polymer chains with variable length. The conjugated polymers investigated here are poly(para-phenylene vinylene) (PPV) and polydiacetylene (PDA). Our results show that the energy of the excited-state increases more than that of the ground-state, as the twist angle increases up to 90º degrees. The change in the twist angle of both polymers leads to a blueshift in luminescence transition energy, the effect being stronger in PPV when the planar segments have similar sizes. The predicted blueshift in both polymers is dependent on the chain length, the effect being more pronounced for shorter-chains.Comunidade Europeia (CE). Fundo Europeu de Desenvolvimento Regional (FEDER)Fundação para a Ciência e a Tecnologia (FCT) - Programa Operacional “Ciência , Tecnologia, Inovação” – POCTI/CTM/41574/2001, CONC-REEQ/443/2001 e SFRH/BD/11231/200

Effect of molecular properties on the performance of polymer light-emitting diodes

The performance of a single layer polymer light-emitting diode depends on several interdependent factors, although recombination between electrons and holes within the polymer layer is believed to play an important role. Our aim is to carry out computer experiments in which bipolar charge carriers are injected in polymer networks made of poly(p-phenylene vinylene) chains randomly oriented. In these simulations, we follow the charge evolution in time from some initial state to the steady state. The intra-molecular properties of the polymer molecules obtained from self-consistent quantum molecular dynamics calculations are used in the mesoscopic model. The purpose of the present work is to clarify the effects of intra-molecular charge mobility and energy disorder on recombination efficiency. In particular, we find that charge mobility along the polymer chains has a serious influence on recombination within the polymer layer. Our results also show that energy disorder due to differences in ionization potential and electron affinity of neighbouring molecules affects mainly recombinations that occur near the electrodes at polymer chains parallel to them.Fundação para a Ciência e a Tecnologia (FCT) – Programa Operacional “Ciência, Tecnologia, Inovação” - POCTI/CTM/41574/2001Comunidade Europeia (CE). Fundo Europeu de Desenvolvimento Regional (FEDER

The effect of the intramolecular properties in single-carrier polymer diodes

The electric behaviour of polymer diodes has the influence of several factors such as the electrodes work function, the experimental conditions used to deposit the active component or the chemistry of the polymer. Although experimentally it is possible to study the effect of some of these factors on the device performance, for instance by changing the chemical structure of the polymer used or the type of electrodes, it is impossible to study individually each one of these effects because changing one of them can influence the others. Quantum mechanical calculations have shown that depending on the chemical structure of the polymer, its intramolecular properties (e.g. ionization potential, electron affinity or intramolecular charge mobility) can be changed. To understand the effect of the intramolecular properties in the performance of polymer diodes we use a generalized dynamical Monte Carlo method that considers the nanostructure of the polymer layer and the main electronic processes involved in diode functioning. Our results show that the influence of the intramolecular properties on the electric behaviour of pristine polymer-diodes with ohmic contacts depends on the morphology of the polymer layer at nanoscale that can alter not only hole and electron current density for the same applied electric field but also charge density and charge distribution inside the polymer layer.Fundação para a Ciência e a Tecnologia (FCT) – POCTI/CTM/41574/2001; CONC-REEQ/443/EEI/2005; SFRH/BD/22143/2005FEDE

Outdoor tourism in the North of Portugal from the perspective of tourist entertainment companies (TEC)

Based on the perception of those responsible for Tourist Entertainment Companies (TEC), the objective of the research is to contribute to the characterization of Outdoor Tourism (OT). Exploratory qualitative research was carried out through 38 in-depth individual interviews. The territory geography, the experiences, and the internal market were considered relevant aspects. In addition, seasonality and climate were identified as significant factors in defining the offer, which can favour the preservation of the environment. Moreover, the risk of the activities was considered low. The interviewees suggested integrating everyone involved in a network to explore the region's potential, as well as to support activities and promote the region. The radical experience, adventure, and getting out of the routine were identified as motivations for the search, as well as contact with nature and the landscape. The research is limited to the North Region of Portugal, and it brings together the most different needs, desires, and expectations for tourism demand. Strengthening OT can favour employability and, consequently, economic and social balance while promotion of the activity can be explored through the customers' previous experience. The evaluations, testimonials, and word of mouth (WOM) being added value that can be optimized through social networks and digital marketing.This project is being carried out within the scope of the TURNOUT Project-Development of Outdoor Tourism of Northern Portugal, POCI-01-0145-ERDF-032289, financed by the European Investment Fund Regional Development (ERDF) through the Operational Program of Competitiveness and Innovation (POCI) and the Foundation for Science and Technology, IP (OE). UNIAG, R&D unit funded by the FCT-Portuguese Foundation for the Development of Science and Technology, Ministry of Science, Technology and Higher Education. “Project Code Reference: UIDB/04752/2020”. This project also thanks to the reviewers of the ICTR21 conference for their improvement inputs to the paper.info:eu-repo/semantics/publishedVersio

Monitoring of outdoor tourism demand

The Herfindahl-Hirschman Index (HHI) was used in order to understand the tourism competitiveness of the different sub-regions that make up the North Region of Portugal. This index is a measure which helps to analyse market concentration and at the same time determines the competitiveness of the market.Project “TURNOUT: Desenvolvimento do Turismo Outdoor da Região Norte de Portugal”, with the reference POCI-01-0145-FEDER-032289 and funded by the European Regional Development Fund (FEDER). This work is, also, funded by National Funds through the Foundation for Science and Technology under the project UIDB/04752/2020.info:eu-repo/semantics/publishedVersio

Supply-side perspectives on outdoor tourism in the North of Portugal

Nowadays, the tourism sector presents many opportunities and challenges. Outdoor Tourism (OT), due to the unusual situation experienced by the pandemic caused by COVID-19, maybe one of the main opportunities to promote the local development of tourist destinations. Most of the literature developed in this context has focused the demand side. Therefore, the investigation intended to fill this gap, considering the perspective of the supply side, taking into account a vision of sustainable development. To meet this gap, the main objective is to contribute to the characterization of Outdoor Tourism (OT) in the North of Portugal, and understand the potential of OT in the perspective of supply., thirty-eight tourist entertainment companies (TEC) were interviewed to assess supply and perceived customers’ motivations. Of the seven Nomenclature of Territorial Units for Statistical Purposes (NUTS), the Northern region was considered to be an area with enormous potential for Nature-related tourist). For the supply side, seasonality and climate were identified as important factors supporting environment preservation. Radical experiences, adventure and getting out of the routine were identified as motivating demand factors, as well as the contact with Nature and the landscape. We have also observed that if we consider the stimulation of the local economy by OT, there is still a lot to do. The evidence pointed to some social imbalance, namely related to employability. Employees were hired according to the evolution of demand, which favours unemployment and social instability. Also, the tourists/costumers are the main channels of communication of the activities; the word-ofmouth (WOM) of costumers’ experiences, personally or through online social media, takes on a prominent role. In this sense, tourists’ online reviews, testimonies, and word-of-mouth can be optimized through social networks and digital marketing. Finally, to evaluate the region's potential for the OT, the interviewees suggested integrating the players involved with the OT into a single network, supporting the activities and promoting the region.The authors would like to thanks the Project “TURNOUT: Desenvolvimento do Turismo Outdoor da Região Norte de Portugal”, with the reference POCI-01-0145-FEDER-032289, and funded by the European Regional Development Fund (FEDER) (through the Operational Programme ‘Innovation and competitiveness’) and by the Portuguese Foundation for the Development of Science (FCT), of the Ministry of Science, Technology and Higher Education. This work is, also, funded by National Funds through the Foundation for Science and Technology under the project UIDB/04752/2020info:eu-repo/semantics/publishedVersio