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Ultrafastenergy relaxation of Cr(acac)3dissolved intetrachloroethylene (TCE) is studied by time-resolved infrared (TRIR)spectroscopy by using electronic and vibrational excitation. Afterelectronic excitation at 400 or 345 nm, the ground state recoversin two time scales: 15 ps (major pathway) and 800 ps (minor pathway),corresponding to fast electronic transition to the ground state andintermediate trapping on the long-lived 2E state followedby intersystem crossing (ISC) to the ground state. The quantum yieldfor the fast recovery of the ground state depends on the excitationwavelength, being higher for 345 nm. Vibrational cooling (VC) occurson the electronic excited states with a time constant of ∼7ps and on the ground electronic state with a time constant of ∼12ps. A kinetic model that explains the observed dynamics is presented.The key point of the model is that the ground-state recovery occursvia thermally activated back-intersystem-crossing (b-ISC) to the quartetmanifold presumably via multiple curve crossings that are sampledwhile the system is vibrationally hot. This underlines the importanceof vibrational cooling as a determining factor for the electronicrelaxation chain. Vibrational excitation of the νCCand νCO vibrations also revealed a subpicosecond (300–700fs) intramolecular vibrational redistribution (IVR) process from thelocalized vibrational states to the bath of vibrational excitations. [ABSTRACT FROM AUTHOR]

The article describes the dynamics of Cr(acac)3 (acac = deprotonated monoanion of acetylacetone) by ultrafast infrared (IR) spectroscopy. According to the authors, the study shows the great value of transient IR spectroscopy in inorganic photophysics. They add the results suggest that most of the ground state population of Cr(acac)3 recovers with a time constant of 15 ps and the rest follows the lifetime of the ²E state.

The synthesis of two triads with two porphyrinyl units linked by oligopyridine derivatives and a new β-functionalized porphyrin-dihydroazepine is described. One of the porphyrin-oligopyridine triads has a quinquepyridine unit connecting the porphyrins β-pyrrolic positions, while the other one has an asymmetric quaterpyridine with one of the pyridines fused to the porphyrin. All compounds have fluorescence emission quantum yields in the range of meso-tetraphenylporphyrin (16-22%). [ABSTRACT FROM AUTHOR]

Chargedmolecules based on the quinolizinum cation have potentialapplications as labels in fluorescence imaging in biological mediaunder nonlinear excitation. A systematic study of the linear and nonlinearphotophysics of derivatives of the quinolizinum cation substitutedby either dimethylaniline or methoxyphenyl electron donors is performed.The effects of donor strength, conjugation length, and symmetry inthe two-photon emission efficiency are analyzed in detail. The bestperforming nonlinear fluorophore, with two-photon absorption crosssections of 1140 GM and an emission quantum yield of 0.22, is characterizedby a symmetric D-π-A+-π-D architecture basedon the methoxyphenyl substituent. Application of this molecule asa fluorescent marker in optical microscopy of living cells revealedthat, under favorable conditions, the fluorophore can be localizedin the cytoplasmatic compartment of the cell, staining vesicular shapeorganelles. At higher dye concentrations and longer staining times,the fluorophore can also penetrate into the nucleus. The nonlinearlyexcited fluorescence lifetime imaging shows that the fluorophore lifetimeis sensitive to its location in the different cell compartments. Usingfluorescence lifetime microscopy, a multicolor map of the cell isdrafted with a single dye. [ABSTRACT FROM AUTHOR]