Title

Enhanced Intersystem Crossing Rate in Polymethine-Like Molecules: Sulfur-Containing Squaraines versus Oxygen-Containing Analogues

Authors

Authors

D. Peceli; H. H. Hu; D. A. Fishman; S. Webster; O. V. Przhonska; V. V. Kurdyukov; Y. L. Slominsky; A. I. Tolmachev; A. D. Kachkovski; A. O. Gerasov; A. E. Masunov; D. J. Hagan;E. W. Van Stryland

Comments

Authors: contact us about adding a copy of your work at STARS@ucf.edu

Abbreviated Journal Title

J. Phys. Chem. A

Keywords

EXCITED-STATE ABSORPTION; SINGLET OXYGEN; QUANTUM YIELDS; SQUARYLIUM; MOLECULES; PHOTODYNAMIC THERAPY; EXCITATION-ENERGIES; 2-PHOTON; ABSORPTION; ORGANIC-MOLECULES; CYANINE DYES; SPECTROSCOPY; Chemistry, Physical; Physics, Atomic, Molecular & Chemical

Abstract

Two different approaches to increase intersystem crossing rates in polymethine-like molecules are presented: traditional heavy-atom substitution and molecular levels engineering. Linear and nonlinear optical properties of a series of polymethine dyes with Brand Se-atom substitution, and a series of new squaraine molecules, where one or two oxygen atoms in a squaraine bridge are replaced with sulfur atoms, are investigated. A consequence of the oxygen-to-sulfur substitution in squaraines is the inversion of their lowest-lying pi pi* and n pi* states leading to a significant reduction of singlet triplet energy difference and opening of an additional intersystem channel of relaxation. Experimental studies show that triplet quantum yields for polymethine dyes with heavy-atom substitutions are small (not more than 10%), while for sulfur-containing squaraines these values reach almost unity. Linear spectroscopic characterization includes absorption, fluorescence, quantum yield, anisotropy, and singlet oxygen generation measurements. Nonlinear characterization, performed by picosecond and femtosecond laser systems (pump probe and Z-scan measurements), includes measurements of the triplet quantum yields, excited state absorption, two-photon absorption, and singlet and triplet state lifetimes. Experimental results are in agreement with density functional theory calculations allowing determination of the energy positions, spin orbital coupling, and electronic configurations of the lowest electronic transitions.

Journal Title

Journal of Physical Chemistry A

Volume

117

Issue/Number

11

Publication Date

1-1-2013

Document Type

Article

Language

English

First Page

2333

Last Page

2346

WOS Identifier

WOS:000316773200007

ISSN

1089-5639

Share

COinS