FLUORESCENCE-DETECTED 2-PHOTON CIRCULAR-DICHROISM OF GD(C4H4O5)(3)]CENTER-DOT-2NACLO(4)CENTER-DOT-6H2O( IN TRIGONAL NA)

Fluorescence-detected two-photon circular dichroism measurements are r eported for Gd3+ in single, uniaxial crystals of Na-3[Gd(C4H4O5)(3)]. 2NaClO(4) . 6H(2)O. These measurements were obtained from experiments in which sample fluorescence is excited by a sequence of one-color opt ical pulses modulated between left- and right-circular polarization st ates. Excitation is along the unique (optic) axis of the crystal sampl e, and fluorescence detection is along the direction of excitation. Th e fluorescence intensities produced by the left- and right-circularly polarized excitation pulses are measured separately and then added and subtracted to obtain the sum and difference quantities, I = I-(L) + I -(R) and Delta I = I-(L) - I-(R). Measurements of Delta I and I as a f unction of excitation wavelength yield spectra related to the circular dichroism (CD) and unpolarized absorption spectra of the sample, and ratios of Delta I to I/2 correspond exactly to absorption dissymmetry factors obtained from direct measurements of CD/absorption spectra. In the study reported here, Delta I and I excitation spectra were measur ed over spectral regions that correspond to two-photon excitation of S -8(7/2) --> P-6(7/2), P-6(5/2), and P-6(3/2) transitions within the 4f (7) electronic configuration of Gd3+ in Na-3[Gd(C4H4O5)(3)]. 2NaClO(4) . 6H(2)O. The two-photon circular dichroism (TPCD) spectra and absorp tion dissymmetry factors obtained from these measurements are the firs t to be reported for any optically active system. The results pose int eresting new challenges for detailed mechanistic analyses of two-photo n absorption processes, and they provide information about molecular t ransition polarizabilities that are unique to chiral systems. Furtherm ore, they suggest that TPCD measurements can yield structural informat ion that both supplements and complements that obtainable from ordinar y (one-photon) circular dichroism experiments.