Reference

Luminescent heterocycles

Luminescent heterocycles. Part 7. 7-(Dimethylamino)-4-hydroxy-3-methylcoumarin, a new laser dye, tunable from 429 nm to 466 nm. Wolfbeis, Otto S. (Inst. Org. Chem., Univ. Graz, Graz, Austria). Monatsh. Chem., 109(4), 905-9 (German) 1978. CODEN: MOCMB7. DOCUMENT TYPE: Journal CA Section: 40 (Dyes, Fluorescent Whitening Agents, and Photosensitizers) In aq. and alc. solns. 7-dimethylamino-4-hydroxy-3-methylcoumarin [64369-56-8] is laser active and exhibits a lasing max. at 434 nm. In acidified solns. the longwave absorption band at 356 nm disappears owing to protonation of the Me2N group. The fluorescence was not entirely quenched; with increasing acidity its max. shifted towards 457 nm, providing a simple method for tuning the lasing frequency. Acid-induced bathochromic emission shifts found with 7-aminolepidone [19840-99-4], 7-methoxylepidone [40053-37-0], 7-ethoxy-4-methylcoumarin [87-05-8] and coumarin 102 [41267-76-9] are interpeted in terms of concurring ground state N- vs. excited state O-protonation.

Three-photon excitation of p-quaterphenyl with a mode-locked femtosecond Ti:sapphire laser

Three-photon excitation of p-quaterphenyl with a mode-locked femtosecond Ti:sapphire laser. Gryczynski, Ignacy; Malak, Henryk; Lakowicz, Joseph R. (School Medicine, University Maryland, Baltimore, MD 21201, USA). Journal of Fluorescence, 6(3), 139-145 (English) 1996 Plenum. CODEN: JOFLEN. ISSN: 1053-0509. DOCUMENT TYPE: Journal CA Section: 73 (Optical, Electron, and Mass Spectroscopy and Other Related Properties) The authors obsd. emission from p-quaterphenyl (p-QT) at 360 nm when exposed to the focused light from a femtosecond (fs) Ti:sapphire laser at 850 nm. This wavelength is too long to allow two-photon excitation of p-QT. The emission intensity of p-QT depends on the cube of the laser power at 850 nm, suggesting that excitation occurs due to a three-photon process. The same emission spectrum and single exponential decay times were obsd.Several reagents with their cas registry numbers 41267-76-9 and 135-70-6 are used here. for three-photon excitation at 850 nm as for two-photon excitation at 586 nm and for 1-photon excitation at 283 nm. The same rotational correlation times were obsd. for 1-, two-, and three-photon excitation, but higher time-zero anisotropies were obsd. for two- and three-photon excitation. The steady-state anisotropies for 1-, two-, and three-photon excitation are precisely consistent with cos2Q, cos4Q, and cos6Q excitation photoselection, where Q is the angle between the elec. field of the incident light and the absorption dipole. These expts. were performed with 3 ′ 10-5 M solns. of p-QT. Use of such low concns. was possible because p-QT displays one of the highest apparent cross sections the authors obsd. to date for three-photon excitation. The spatial distribution of the excited fluorescence was less for three-photon excitation than for two-photon excitation of Coumarin 102 at the same 850 nm excitation wavelength. The high cross section, photostability, and clear cos6Q photoselection of p-QT make it an ideal three-photon std. for spectroscopy and microscopy. .