Search

The present work is aimed at a deeper investigation of two recently synthesized heteroaromatic fluorophores by means of a computational multilayer approach, integrating quantum mechanics (QM) and molecular mechanics (MM)., The present work is aimed at a deeper investigation of two recently synthesized heteroaromatic fluorophores by means of a computational multilayer approach, integrating quantum mechanics (QM) and molecular mechanics (MM). In particular, dispersion of the title dyes in a polymer matrix is studied in connection with potential applications as photoactive species in luminescent solar concentrators (LSCs). Molecular dynamics simulations, based on accurate QM-derived force fields, reveal increased stiffness of these organic dyes when going from CHCl3 solution to the polymer matrix. QM/MM computations of UV spectra for snapshots extracted from MD simulations show that this different flexibility permits explaining the different spectral shapes obtained experimentally for the two different environments. Moreover, the general spectroscopic trends are reproduced well by static computations employing a polarizable continuum description of environmental effects.

We report on vapochromic films suitable for detecting volatile organic compounds (VOCs), based on polycarbonate (PC) doped with 4-(triphenylamino)phthalonitrile (TPAP), a fluorescent molecular rotor sensitive to solvent polarity and viscosity. PC films of variable thickness (from 20 up to 80 mu m) and containing small amounts of TPAP (0.05wt%) were prepared and exposed to a saturated atmosphere of different VOCs. TPAP/PC films showed a gradual decrease and red-shift of the emission during the exposure to solvents with high polarity index and favorable interaction with the polymer matrix such as THF, CHCl3, and acetonitrile. In the case of the most interacting solvents (THF and CHCl3), TPAP/PC films also showed a fluorescence increase at longer exposure times, as a consequence of an irreversible, solvent-induced crystallization process of the polymeric matrix. The vapochromism of TPAP/PC films is rationalized on the basis of alterations of the rotor intramolecular motion upon solvent uptake by PC and polarity effects of the microenvironment. Interestingly, the fluorescence response of the TPAP/PC films shows a non-trivial, tuneable dependence on film thickness during the second solvent-exposure stage. The latter effect is attributed to a variable extent of the crystallization process occurring in the PC films. This observation promptly suggests, in turn, an effective procedure to modulate the spectroscopic response in such functionalized polymeric materials through the precise control of the film thickness. Copyright (c) 2015 John Wiley & Sons, Ltd.

Sunlight concentration is a promising path to cost-effective photovoltaic (PV) technologies. Compared to standard concentrators based on geometrical optics, luminescent solar concentrators (LSCs) appear to be viable and convenient alternatives because sunlight concentration to PV occurs with diffuse light and there is no need for sun tracking or cooling apparatuses. In this study, we report on the optical efficiencies of luminescent solar concentrators (LSCs) based on poly(methyl methacrylate) (PMMA) thin films doped with a red-emitting zinc(II) complex of the D-A-D type ligand N, N'-bis(2-hydroxy-1-naphthylidene)-diaminomaleonitrile (ZnL). ZnL is attractive for use in LSC owing to its easy and cheap synthesis. ZnL in PMMA shows an emission band at 624 nm, a Stokes shift of 34 nm and an average QY of 23%, data comparable to those recorded in solution and efficiently predicted by DFT calculations. A study of ZnL/PMMA LSC yields optical efficiencies of 7%, which is comparable to those based on the near unity QY fluorophores such as Lumogen Red. These performances were attributed to the higher emission red-shift and larger Stokes shift of ZnL that prevent the loss of efficiencies due to self-absorption and possibly circumvent its lower QY.

We report on the synthesis of new fluorescent symmetrical 2,5-diaryl-1-methylimidazoles obtained in good yields by using direct C-H arylation synthetic strategies. Spectroscopic investigations in THF solution evidenced that the 2,5-diarylimidazole bearing the strong electron-withdrawing cyanoacrylate groups achieved the best trade-off between fluorescence maximum (518 nm), Stokes shift (115 nm) and a quantum yield of 25%. Highly homogeneous dispersions of the selected fluorophore in poly(methyl methacrylate) (PMMA) thin films (25 ± 5 μm of thickness) perfectly maintained the optical features in solution, thus providing a brilliant green emission and a markedly enhanced quantum yield of 55%. Photocurrent measurements of the PMMA collectors supported the use of 2,5-diaryl-1-methylimidazoles as accessible alternatives to perylene backbones for the development of LSC with optical efficiencies close to 7%.

The vapochromic properties of a fluorescent 3-[2-(4-nitrophenyl) ethenyl]-1-(2-ethylhexyl)-2-methylindole (NPEMI-E) characterized by intramolecular charge transfer (ICT) character, dispersed in polycarbonate (PC) films is reported. NPEMI-E solvatochromism is investigated by means of experimental and computational methods. Fluorescent PC films containing 0.1 wt % of NPEMI-E are prepared and exposed to saturated atmospheres of different volatile organic compounds (VOCs). NPEMI-E/PC films show remarkable and reversible vapochromism when exposed to VOCs with high polarity index and favorable interaction with PC matrix such as CHCl3. Only minor variations in the emission wavelength are actually recorded for all other classes of VOCs investigated. The hue parameter is also used for the effective extraction of spectral information from digital color images without the need for wavelength discriminators. Overall, the present results support the use of NPEMI-E/PC films for the cost-effective detection of CHCl3 vapors. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017.

We report on a new vapochromic system suitable for sensing volatile organic compounds (VOCs) based on polymer films doped with 4-(diphenylamino)phthalonitrile (DPAP), a fluorescent molecular rotor sensitive to both solvent polarity and viscosity. Poly(methyl methacrylate) (PMMA) and polycarbonate (PC) films containing small amounts of DPAP (≤0.1 wt%) were prepared and exposed to saturated atmospheres of different VOCs. DPAP/PMMA films show a good and reversible vapochromism when exposed to VOCs with high polarity index and favourable interaction with polymer matrices such as THF, CHCl3, and acetonitrile. Analogously, DPAP/PC films exposed to polar and highly polymer-interacting solvents, that is, toluene, THF, and CHCl3, show a gradual decrease and red-shift of the emission. In contrast to DPAP/PMMA films, an unexpected increase and further red-shift of fluorescence are observed at longer exposure times as a consequence of an irreversible, solvent-induced crystallization process of PC. The vapochromism of DPAP-doped films is rationalized on the basis of alterations of the rotor intramolecular motion and polarity effects stemming from the environment, which, in concert, influence the deactivation pathways of the DPAP intramolecular charge transfer state. Overall, the present results support the use of DPAP-enriched plastic films as a new chromogenic material suitable for the detection of VOCs.