Anisotropic Intersystem Crossing from the Upper Excited Triplet States of Anthracenes: Two-laser Time-Resolved EPR Study

Abstract

A two-laser, two-color time-resolved EPR (TREPR) technique has been applied to the investigation of the electron spin polarization in the excited triplet states of anthracene and its halogen anthracene in rigid glassy matrixes. The one-laser excitation of anthracenes with 355 nm gave the triplet TREPR spectra of the lowest excited triplet (T1) states with EEE/AAA polarization pattern. For 9-bromoanthracene and 9,10-dibromoanthracene, the reexcitation by a dye laser (442 nm) to the upper excited triplet (T n : n > 3) states brought about the opposite phase polarization in the T1 states. The phenomena were interpreted in terms of the sublevel selective reverse intersystem crossing (RISC) from the T n (n = 2 or 3) state to the S1 state. The time profiles of the polarization were analyzed taking into account the anisotropic RISC processes. On the other hand, for anthracene and 9,10-dichloroanthracene, little effect was observed on the electron spin polarization by two-step laser irradiation.

Enhancing Fluorescence Brightness: Effect of Reverse Intersystem Crossing Studied by Fluorescence Fluctuation Spectroscopy

“…From T n the dye can efficiently cross back to the singlet system, where fluorescence emission occurs 17–20. ReISC has previously been shown for dyes with high ISC yields such as bipyridien,17 erythrosine B,18, 21, 22 rose bengal,18, 21–25 cyanine dyes,19, 20 anthracene,26 eosin Y21, 22 and propiophenone 27. ReISC had to be included in fluorescence statistics of single‐molecule experiments of sulforhodamine 101 or DiI in polymethylmethacrylat (PMMA),28 terrylene in p ‐terphenyl crystals,29 merocyanine 540 in solution,30 and of cyanine 5 (Cy5) in poly(vinyl‐alcohol) (PVA),31 on air‐glass interfaces,32 under nitrogen atmosphere33 or in Förster resonance energy transfer (FRET) experiments 34.…”

Two-laser two-color time-resolved EPR study on higher-excited-state triplet-singlet intersystem crossing of porphyrins and phthalocyanines

“…ESP in the T l state is produced by anisotropic intersystem crossing (ISC) between the excited singlet and triplet states. Recently, we reported the production of ESP in the process of reverse ISC from higher-lying triplets in anthracene and its derivatives with two-laser two-color TREPR spectroscopy [1]. Single-laser excitation to the excited singlet states gave polafized EPR speetra due to the lowest excited triplet (T1) state, and the polarization patterns were well interpreted by the symmetry selection rules.…”

“…5, we made a quantitative analysis of the time evolution of the ESP in the T l state and estimated the quantum yield (~rs) of the reverse ISC process as previously described [1]. The initial TREPR signal intensity (I0) is proportional to the t¡ let concentration as well as to the population differenee between two sublevels in the T I state.…”

Study of Anisotropic Interfacial Electron Transfer Across a Semiconductor/Solution Interface by Time‐Resolved EPR Spectroscopy

“…The detection system for the TREPR signal has been described elsewhere. [17] A helium-flow cryostat (Oxford ESR900) was utilized for measurements at low temperatures.…”