Solvent dependence of the inhibition of intramolecular charge-transfer in N-substituted 1,8-naphthalimide derivatives as dye lasers

Fluorescence, lasing efficiency and photostability of the 4-methoxy and 4-acetamide-N-substituted 1,8-naphthalimide derivatives in alcohols have been investigated. An intramolecular charge-transfer (CT) inhibits the fluorescence and laser emission in the derivatives with an amino terminal group in the side chain. The addition of protons (acetic acid) quenches the intramolecular CT, and a high lasing efficiency in the green-blue zone of the spectrum is obtained with a Nz pulsed laser (FWHM similar or equal to 5.5 ns). The results have been interpreted on the basis of the acidity, polarity and viscosity of the solvents. Photostability tests with a pulsed N-2 laser and a Xe lamp (150 W) show good behavior for all molecules, except in ethylene glycol.