Excimer formation in 1-pyrenyl-methane-amine

The absorption, corrected excitation and emission spectra, as well as the fluorescence lifetimes of 1-pyrenyl-methane-amine (1), prepared from 1-pyrene-carboxaldehyde via its oxime, have determined in deoxygenated hexane solutions in the 1.5×10−6–4.0×10−4 M concentration range at 20°C. The absorption spectrum of 1 in hexane has been found to have bands with maxima at 275 nm (ϵ=5.2×104 M−1 cm−1, 312 nm (ϵ=1.2×104 M−1 cm−1), 325 nm (ϵ=2.9×104 M−1 cm−1) and 341 nm (ϵ=4.3×104 M−1 cm−1) and to obey the Beer—Lambe law. Further, the ratio PA of the absorption intensity of the most intense band above 300 nm to that of the adjacent minimum at the shorter wavelength has been found to be 3.1, the corrected excitation spectrum has been found to be almost identical with that of the absorption spectra, and the peak-to-valley ratio PM for the (0—0) transition in the excitation spectrum viewed at the monomer emission has been determined to be 2.7. These criteria have established the absence of ground-state association of 1 in hexane in the concentration range investigated. Excitation of 3.0×10−6 M 1 in hexane has resulted in the appearance of fluorescence with an emission maximum at 374 nm, which corresponded to the excited monomer 1*. Increasing the concentration of 1 resulted in the progressive emergence of a new emission band with a maximum at 475 nm. This behavior has been rationalized in terms of the formation of (1—1)* excimer. Determination of the fluoroscence lifetimes at the monomer and excimer emission bands at different concentrations of 1 has permitted the elucidation of the rate constants for the formation (κDM=1.48×10 M−1 s−1 and decomposition (κMD=2.4×106 s−1) of (1-1)* and those for the monomer (κM=3.73×106 s−1) and excimer (κD=1.55×107 s−1) decays. The observed properties have rendered 1 to be a good fluorescence probe.