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 [ε_max,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.