Permanent hole burning with a diode laser: excited-state dynamics of bacteriochlorophyll in glasses and micelles

Abstract

A temperature- and current-controlled diode laser at ∼780 nm was used to perform permanent hole-burning experiments on the S1 ← S0 0–0 (Qy) transition of bacteriochlorophyll a (BChl a) in amorphous hosts. Hole widths were obtained for the glass triethylamine (TEA) between 0.4 and 15 K, for micelles of the detergent lauryldimethylamine N-oxide (LDAO) between 1.2 and 4.2 K, and for wet and dry CCl4 at 1.2 K. The homogeneous linewidth, Γhom, of BChl a in TEA follows a T1.3±0.1 dependence at temperatures T < 7 K, whereas at T ≈ 7 K a crossover to an exponential dependence with an activation energy of 33 ± 3 cm−1 is observed. The results, when compared with those obtained for free-base porphin in the same glass, suggest that a low-frequency mode of TEA is responsible for the dephasing. From the experiments on micelles conclusions are drawn about the molecular conformations of BChl a in the detergent.