Hydrogen bonding,polarity and matrix effects on the spectroscopic and photophysical properties of some N- and 3-substituted derivatives of carbazoles

Fluorescence spectra and photophysical properties of N-cyano and N-carboethoxy carbazole derivatives have been compared to the equivalent 3-substituted compounds in fluid polar and unpolar solutions and in a low temperature rigid matrix at 77 K. The 3-carboethoxy derivatives have been shown to form an excited state complex (exciplex) with ethanol in fluid solutions. On the other hand the photophysical properties of the N-substituted derivatives are much affected by the solvent polarity in fluid solutions in that the radiationless decay rate constants show a marked increase in these media. A tentative explanation has been given in terms of the relative energy gap existing between the ¹L_b and the ¹L_a states of these molecules.