| Abstract
| - With 4-(dimethylamino)phenylacetylene (DACET) in p-dioxane/water mixtures, efficient fluorescencequenching of the locally excited (LE) state occurs, becoming more efficient with increasing water content.This quenching does not lead to the appearance of an emission from an intramolecular charge-transfer (ICT)state, in contrast to what is found with 4-(dimethylamino)benzonitrile (DMABN). With DMABN in p-dioxaneand its mixtures with water, picosecond LE and ICT fluorescence decays are observed, with a shortest decaytime down to 3 ps for p-dioxane/water (50/50). A similar quenching process takes place with the planarized1-methyl-6-cyano-1,2,3,4-tetrahydroquinoline (NMCQ), for which molecule ICT has not been found. It isconcluded that there is no experimental evidence or photophysical argument that ICT occurs with DACET inp-dioxane/water mixtures or other polar solvents, contrary to what was recently reported on the basis ofnanosecond single-photon-counting (SPC) experiments (N. Chattopadhyay et al. J. Phys. Chem. A2001, 105,10025). A comparison between the results of picosecond and nanosecond SPC measurements with DMABN,DACET, and NMCQ is made.
|
