Laser pumped magnetophotoselection in triplet dyes

Abstract

Some observations have been made on the Δm=±2 and Δm=±1 ESR spectra in rhodamine (type R), fluorescein (type F), and acridine (type A) dyes, important laser active media, during laser excitation at 77 K. The results have revealed that the spectra and the lifetimes of the dyes in the T₁ states in ethanol are affected significantly by the chromophoric structure. The root‐mean‐square value of zero‐field splitting parameters (ZFSP), D*, and the triplet‐state lifetime, τ_T, increase in the order type R < type A < type F and type F < type R < type A, respectively. By the method of magnetophotoselection, the Δm=±1 absorption lines of acridine orange and fluorescein disodium salt dyes are assigned to three directions along the molecular axes. Furthermore, the ZFSP values and the polarization results show that the π‐electron distribution is most strongly polarized along the long axis of the chromophore in the case of type F dyes.