Electronic relaxation of acridine as studied by picosecond spectroscopy

Abstract

Internal conversion (IC) and intersystem crossing (ISC) rates of the lowest excited singlet state (S₁) of acridine have been measured in n‐hexane at room temperature by picosecond spectroscopy. The rates deduced from the buildup of triplet–triplet absorption and the quantum yield of intersystem crossing were found to be 3×10¹⁰ sec⁻¹ for the internal conversion and 3×10¹⁰ sec⁻¹ for the intersystem crossing. Corresponding rates for perdeuterated acridine are found to be similar. These rates, when combined with the upper limit of the unobserved fluorescence, lead to the nπ* assignment of the lowest excited singlet state. The kinetics of repopulation of the ground state following a pulsed excitation of the sample give strong indication of the occurrence of S₁→S₀ internal conversion.