1,721,012 research outputs found
Solvent and temperature effects on the fluorescence and competitive photoreactions of cis-9-styrylanthracene
No full textCompetition between photoisomerization and photocyclization of the cis isomers of n-styrylnaphthalenes and -styrylphenanthrenes.
No full textQuantitative cascade energy transfer in semiconductor thin films
No full textIn this contribution we report the photophysical study of three organic blend systems comprising [60]-PCBM along with different combinations of five extended semiconducting arylacetylenes, i.e. p-[(2-{[m, pdidodecyloxyphenyl] ethynyl}-7-fluorenyl) ethynyl] benzonitrile, 4,7-bis(5-{[m, p-bis(hexyloxy) phenyl]ethynyl} thien-2-yl)-2,1,3-benzothiadiazole, 9,10-bis-[(m, m-bis{[m, m-bis-(hexyloxy) phenyl] ethynyl}phenyl) ethynyl]-anthracene, pseudo-p-[(10-{[m, p-bis-(hexyloxy) phenyl] ethynyl}-9-anthryl[2.2] paracyclophane, and oligo{2,5-bis(hexyloxy)[1,4-phenylene ethynylene]-alt-[9,10-anthraceneethynylene]}, and one semiconducting arylvinylene, i.e. 9,10-bis-{(E)-[m, p-bis(hexyloxy) phenyl] vinyl}-anthracene, that evidenced an efficient quantitative energy transfer from the hypsochromic to the bathochromic species (the potential efficient charge-donor components), useful to extend the collection of sunlight. An interesting emission enhancement in thin films has been observed only for the arylvinylene derivative
The role of the adiabatic mechanism in the photoisomerization of 1,2-diarylethenes and related compounds
No full textPrincipal-component self-modeling analysis of fluorescence for some trans-diarylethylenes. A comparison with kinetic analysis
No full textComprehensive photophysical behaviour of ethynyl-fluorenes and ethynyl-anthracenes investigated by fast and ultrafast time-resolved spectroscopy
No full textDetailed investigations by time-resolved transient absorption and fluorescence spectroscopies with nano- and femtosecond time resolutions are carried out with the aim of characterising the lowest excited singlet and triplet states of three ethynyl fluorenes (13) and three ethynyl anthracenes (46) in solvents of different polarity. The solvent is found to modify the deactivation pathways of the lowest excited singlet state of compounds 14, thus changing their fluorescence, intersystem crossing and internal conversion efficiencies. The fluorescence and triplet yields gradually decrease, while the internal conversion quantum yield increases upon increasing the solvent dielectric constant. These experimental results, coupled with the marked fluorosolvatochromic effect, point to the involvement of an emitting state with a charge-transfer (CT) character, strongly stabilised by polar solvents. This is proved by ultrafast spectroscopic studies in which two transients, distinguished by characteristic spectral shapes assigned to locally excited (LE) and CT states, are detected, the CT state being the longer lived and fluorescent one in highly polar solvents. The intramolecular LE?CT process, operative in highly polar media, becomes particularly fast (up to 300 fs) in the case of the NO2 derivative 1. No pushpull character is found for 5 and 6, which exhibit different photophysical behaviour; indeed, the solvent polarity does not modify significantly the dynamics of the lowest excited singlet states. Quantum mechanical calculations at the TDDFT level are also used to determine the state order and nature of the lowest excited singlet and triplet states and to rationalise the different photophysical behaviour of fluorine and anthracene derivatives, particularly concerning the intersystem crossing process
Unusual high fluorescence of two nitro-distyrylbenzene-like compounds induced by CT processes affecting the fluorescence/intersystem-crossing competition
No full textTwo nitro-substituted 1,4-distyrylbenzene-like compounds have been investigated using stationary and time- resolved (ns/fs) spectrometric techniques as a function of solvent polarity. In the two compounds the central benzene ring is substituted with a p-nitrostyryl group at one side while, at the other side, compound 1 (asymmetric) bears a pyrid-4-ylethenyl group and compound 2 (symmetric) another p-nitrostyryl group. The solvent dependent intramolecular charge transfer (ICT) in the singlet manifold was found to strongly affect the competition among fluorescence, intersystem crossing and trans–cis photoisomerization. The presence of nitro-groups in the 1,4-distyrylbenzene skeleton causes the usual strong decrease of fluorescence in favour of intersystem crossing to a reactive triplet state. However, the favoured formation of the ICT state in polar solvents induces an unexpected important increase of the fluorescence quantum yield (three/two order of magnitude for the nitro and dinitro derivatives, respectively). The ultrafast spectral transients helped to understand the solvent effects measured by stationary techniques and gave information on the dynamics of the locally excited singlet state (1LE*) and the 1ICT* state, fast produced in polar solvents. Evidence of dual fluorescence in a limited range of solvent polarity, particularly for compound 1, is also reported. The role of an upper triplet state in a non-polar solvent is discussed also based on quantum- mechanical calculations (TD-DFT method) and temperature effects on the photophysical parameters
Adiabatic Pathways in the Conformational and Geometrical Photoisomerization of the 1,2-Distyrylbenzene Isomers
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Competitive radiative and reactive relaxation channels in the excited state decay of some thioanalogues of EE-distyrylbienzene G..
No full textThe photophysical and photochemical properties of some thio-analogues of symmetrically substituted EE-1,4-distyrylbenzene (linear conjugation) and EE-1,3-distyrylbenzene (crossed conjugation), where thiophene rings replace the side benzene rings or the central benzene ring, have been investigated. The kinetic competition between the radiative and reactive relaxation channels of the lowest excited singlet state has been compared with that found for the corresponding hydrocarbons. The photobehaviour markedly depends on the type of conjugation and on the position (2’ or 3’) of the ethenic bridge with respect to the sulfur atom. The main effect of the heteroatom is an increase in the photoisomerization yield due to a decrease of the torsional barrier in S1 and to an increase in the S1T1 intersystem crossing, which opens the way to isomerization in the triplet manifold. Conformational equilibria, due to restricted rotation around the quasi single bonds with the ethenic carbons, have also been investigated by selective photoexcitation for the compounds with side 3’-thienyl groups
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