First-principles simulations of the initial phase of self-aggregation of a cyanine dye: structure and optical spectra

Using first-principles simulations, we investigated the initial steps of the self-aggregation of the dye pseudoisocyanine (PIC) in water. First, we performed molecular dynamics (MD) simulations of the self-aggregation process, in which pile-of-coins oligomers ranging from dimers to stacks of about 20 molecules formed. The oligomer structures were found to be very flexible, with the dimers entering a weakly coupled state and then returning to a stable π-π stacked conformation on a nanosecond time scale. The structural information from the MD simulations was combined with quantum chemical calculations to generate a time-dependent Frenkel exciton Hamiltonian for monomers, dimers, and trimers, which included vibronic coupling. This Hamiltonian, in turn, was used to calculate the absorption spectra for these systems. The simulated dimer spectrum compared well to experiment, validating the face-to-face stacked dimer arrangement found in our MD simulations. Comparison of the simulated trimer spectrum to experiment suggested that oligomers larger than the dimer cannot be abundant at the onset of J-aggregation. Finally, the conformation of the PIC J-aggregate was investigated by testing the stability of several possible conformations in our MD simulations; none of the tested structures was found to be stable

Polariton effects in molecular crystals studied by classical and quantum-electrodynamic approaches

A quantum-electrodynamic approach is studied as an alternative to the classical description of polaritons in molecular crystals, with the focus on future interpretation of oligothiophene spectra. As expected, the results of the two approaches coincide, but the quantum description is better suited for future generalizations, notably for detailed studies of vibronic coupling. The quantum approach is used here to probe the importance of inherent polaritonic effects. They are found to be minor, being superseded by vibronic interactions; the latter are responsible for most peculiarities observed in oligothiophene spectra

Exciton level structure and dynamics in tubular porphyrin aggregates

We present an account of the optical properties of the Frenkel excitons in self-assembled porphyrin tubular aggregates that represent an analog to natural photosynthetic antennae. Using a combination of ultrafast optical spectroscopy and stochastic exciton modeling, we address both linear and nonlinear exciton absorption, relaxation pathways, and the role of disorder. The static disorder-dominated absorption and fluorescence line widths show little temperature dependence for the lowest excitons (Q band), which we successfully simulate using a model of exciton scattering on acoustic phonons in the host matrix. Temperature-dependent transient absorption of and fluorescence from the excitons in the tubular aggregates are marked by nonexponential decays with time scales ranging from a few picoseconds to a few nanoseconds, reflecting complex relaxation mechanisms. Combined experimental and theoretical investigations indicate that nonradiative pathways induced by traps and defects dominate the relaxation of excitons in the tubular aggregates. We model the pump?probe spectra and ascribe the excited-state absorption to transitions from one-exciton states to a manifold of mixed one- and two-exciton states. Our results demonstrate that while the delocalized Frenkel excitons (over 208 (1036) molecules for the optically dominant excitons in the Q (B) band) resulting from strong intermolecular coupling in these aggregates could potentially facilitate efficient energy transfer, fast relaxation due to defects and disorder probably present a major limitation for exciton transport over large distances. We present an account of the optical properties of the Frenkel excitons in self-assembled porphyrin tubular aggregates that represent an analog to natural photosynthetic antennae. Using a combination of ultrafast optical spectroscopy and stochastic exciton modeling, we address both linear and nonlinear exciton absorption, relaxation pathways, and the role of disorder. The static disorder-dominated absorption and fluorescence line widths show little temperature dependence for the lowest excitons (Q band), which we successfully simulate using a model of exciton scattering on acoustic phonons in the host matrix. Temperature-dependent transient absorption of and fluorescence from the excitons in the tubular aggregates are marked by nonexponential decays with time scales ranging from a few picoseconds to a few nanoseconds, reflecting complex relaxation mechanisms. Combined experimental and theoretical investigations indicate that nonradiative pathways induced by traps and defects dominate the relaxation of excitons in the tubular aggregates. We model the pump?probe spectra and ascribe the excited-state absorption to transitions from one-exciton states to a manifold of mixed one- and two-exciton states. Our results demonstrate that while the delocalized Frenkel excitons (over 208 (1036) molecules for the optically dominant excitons in the Q (B) band) resulting from strong intermolecular coupling in these aggregates could potentially facilitate efficient energy transfer, fast relaxation due to defects and disorder probably present a major limitation for exciton transport over large distances

Promotion of men’s mental health

Introduction: Despite the fact that the knowledge of health differences between males and females is more and more available, it does not always translate into the differentiation of health programmes. Undoubtedly, there is a need for innovative programmes promoting the mental health of men and accounting for male standards. Material and methods: Review of scientific literature concerning mental health promotion, with special regard to recommendation to create programmes of promotion of men’s mental health searched in Pubmed, Scopus and Google Scholar. Results: Health promotion is a process enabling people to increase their control over health and to improve it. Mental health promotion is a rarely discussed branch of health promotion, and its characteristics differ from physical health promotion. Currently, no organised activities are conducted in Poland aiming at the promotion of men’s mental health. Looking at suicide statistics, according to which men take their lives seven times more often than women, it seems essential to design comprehensive activities targeting this specific group. Male-specific determinants of mental health should constitute a reference point for health promoters in the process of designing programmes of mental health promotion. Conclusions: It seems necessary to consider gender factor while designing activities related to mental health promotion. The activities directed to men should be planned according to specific principles. Their implementation may have a positive effect on male participation and involvement in the suggested programme of mental health promotion, and in turn on its efficacy.Introduction: Despite the fact that the knowledge of health differences between males and females is more and more available, it does not always translate into the differentiation of health programmes. Undoubtedly, there is a need for innovative programmes promoting the mental health of men and accounting for male standards. Material and methods: Review of scientific literature concerning mental health promotion, with special regard to recommendation to create programmes of promotion of men’s mental health searched in Pubmed, Scopus and Google Scholar. Results: Health promotion is a process enabling people to increase their control over health and to improve it. Mental health promotion is a rarely discussed branch of health promotion, and its characteristics differ from physical health promotion. Currently, no organised activities are conducted in Poland aiming at the promotion of men’s mental health. Looking at suicide statistics, according to which men take their lives seven times more often than women, it seems essential to design comprehensive activities targeting this specific group. Male-specific determinants of mental health should constitute a reference point for health promoters in the process of designing programmes of mental health promotion. Conclusions: It seems necessary to consider gender factor while designing activities related to mental health promotion. The activities directed to men should be planned according to specific principles. Their implementation may have a positive effect on male participation and involvement in the suggested programme of mental health promotion, and in turn on its efficacy

The effect of intermolecular interaction on excited states in p − DTS(FBTTH 2

Using optical spectroscopy in solution and thin film, and supported by quantum chemical calculations, we investigated the aggregation process of the donor-acceptor type molecule p − DTS(FBTTH2)2. We demonstrate that cooling a solution induces a disorder-order phase transition that proceeds in three stages analogous to the steps observed in semi-rigid conjugated polymers. By analyzing the spectra, we are able to identify the spectral signature of monomer and aggregate in absorption and emission. From this we find that in films, the fraction of aggregates is near 100% which is in contrast to films made from semi-rigid conjugated polymers

Traditional mentor relationships in the lives of creative people Toward an aesthetic understanding

SIGLEAvailable from British Library Document Supply Centre-DSC:DXN026103 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Genre, schema, and the academic writing process An enquiry into the generalisability of generic structure and its relationship to schematic knowledge

SIGLEAvailable from British Library Document Supply Centre-DSC:DXN029010 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Shape of the Q band in the absorption spectra of porphyrin nanotubes: Vibronic coupling or exciton effects?

Absorption and linear dichroism spectra of self-assembled tubular aggregates of TPPS4 porphyrin are studied theoretically with special emphasis on the low energy part of the spectra (the Q band region) where the coupling with intramolecular vibrations is pronounced. The model Hamiltonian includes both the excitonic coupling between four molecular electronic excited states contributing to the porphyrin Q and B bands as well as the intermediate-strength linear exciton-phonon coupling to one effective high-frequency molecular vibrational mode. Good agreement between the calculated and experimental spectra is obtained. The results allow us to identify the nature of the peaks observed in the Q band region of the aggregate’s absorption spectrum; we show that the two most prominent peaks within the Q band originate from two different excitonic subbands. It is shown that the coupling between the Q and B bands plays an important role and the vibronic coupling affects the details of the absorption lineshape.