Flash photolysis of cyanine dyes. Pinacyanol chloride (1,1′-diethyl-2,2′-carbocyanine chloride)

Abstract

The dye pinacyanol chloride (1,1′-diethyl-2,2′-carbocyanine chloride) has been studied using a conventional flash photolysis technique. The absorption spectrum and molar extinction coefficient of the triplet state have been determined [εmax,635nm=(5.8 ± 0.3)× 104 dm3 mol–1 cm–1]. The quantum efficiency for intersystem crossing to the triplet state has an upper limit of 10–2 in methanol, ethylene glycol and glycerol. Photoisomerization is absent in the three solvents. The main pathway for deactivation of the excited singlet state S1 is therefore the non-radiative process of internal conversion S1→ S0.