Sensitized fluorescence of aromatic hydrocarbons in solution. Spectrophotometric estimation of energy transfer coefficients at high and low optical densities

Abstract

Conditions have been examined for the measurement of electronic excitation energy transfer coefficients for dissolved aromatic donor + acceptor systems at high and low optical density limits. Transfer coefficients obtained for the phenanthrene + anthracene system at both limits in air-saturated ether are in good agreement with that expected for a diffusion-limited process; the ¹L_a and ¹L_b states of azulene respectively sensitize and quench the ¹L_a fluorescent state of anthracene, and naphthalene sensitizes the second excited ¹L_a fluorescent state of azulene. The extremely low self-quenching constants found for naphthalene and phenanthrene are attributed to rapid excimer dissociation under the prevailing conditions; the evidence indicates that this process is also responsible for the low self-quenching constant found for anthracene, and it is suggested that azulene self-quenching involves self-sensitization of the lowest excited (non-fluorescent)¹L_b state.