Nonequilibrium vibrational excitations of para-nitroaniline (PNA, 4-nitroaniline) occurring after internal conversion from the photoexcited charge transfer state are studied by picosecond anti-Stokes Raman scattering. Vibrational excess populations with distinctly different picosecond rise and decay times are found for a number of modes with frequencies between 860 and 1510 cm−1, including the overtone of a non-Raman active mode. A nonthermal distribution of vibrational populations exists up to about 6 ps after photoexcitation. The time-resolved experiments are complemented by steady-state infrared and Raman measurements as well as calculations based on density functional theory, providing a detailed analysis of the steady-state vibrational spectra of PNA and two of its isotopomers. A weakly Raman active vibration at about 1510 cm−1 displays the fastest rise time and a pronounced excess population and—thus—represents the main accepting mode. We suggest that an out-of-plane mode giving rise to the overtone Raman band at this frequency acts both as coupling and accepting mode in the internal conversion process.
Zinc oxide nanoparticles (ZnO NPs) are commonly used as UV filters in commercial sunscreen products. Their penetration into the skin is intensively discussed in the literature. In the present in vivo study, penetration of ZnO NPs (30 nm in size) into human skin was investigated by multiphoton tomography. Based on the non-linear effects of a second harmonic generation and hyper-Rayleigh scattering, the distribution of ZnO NPs in the horny layers of the epidermis, as well as the furrows, wrinkles and orifice of the hair follicles was analyzed. This method permitted distinguishing between the particulate and dissolved forms of Zn. A detection limit of 0.08 fg/µm3 was estimated. Taking advantage of this sensitivity, it was clearly shown that ZnO NPs penetrate only into the outermost layers of stratum corneum, furrows and into the orifices of the hair follicles and do not reach the viable epidermis.
The syntheses of cationic ruthenium(II)
allenylidene complexes
[(1a−e)PF6] of the
type
[CpRu(CCCR2)(PPh3)2]PF6
(1a, R2C: = cycloheptatrienylidene;
1b, R2C: = 2,7-dimethyl-4,5-benzocycloheptatrienylidene; 1c, R2C: =
2,7-diphenyl-4,5-benzocycloheptatrienylidene;
1d, R2C: =
dibenzo[a,e]cycloheptatrienylidene;
1e, R2C: =
4,5-dihydrodibenzo[a,e]cycloheptatrienylidene) are reported. In the series
1a−e, the decreasing ability of
R2C: to stabilize
a positive charge results in a tuning of the electronic and optical
properties by changing the
relative contributions of the two canonical forms
[Ru+]CCCR2 (A) and
[Ru]C⋮CCR2
+
(B), which is studied particularly by NMR and UV/visible
spectroscopy. The first molecular
hyperpolarizabilitiy β of (1b)PF6 has
been determined by hyper Raleigh scattering. The
X-ray crystal structures of (1b)PF6,
(1d)PF6·CH2Cl2,
and the acetylide complex CpRu(C⋮C−C7H7-2,4,6)(PPh3)2
are presented.
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