Photophysics of cyanine dyes: Subnanosecond relaxation dynamics in monomers, dimers, and H- and J-aggregates in solution

Journal Article · Thu Apr 03 04:00:00 EST 1997 · Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical

DOI:https://doi.org/10.1021/jp9621134· OSTI ID:535438

Khairutdinov, R F ^[1]; Serpone, N ^[2]

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1. Inst. of Chemical Physics, Moscow (Russian Federation)
2. Concordia Univ., Montreal (Canada)

The photophysics of three cyanine dyes (i) 1,1`-diethyl-2,2`-cyanine iodide (pseudoisocyanine, PIC), (ii) 3,3`-didodecyldithia-2, 2`-carbocyanine bromide (dye 1), and (iii) 3,3`-diethyldithia-2, 2`-carbocyanine iodide (dye 2) have been examined by picosecond-laser photolysis in aqueous and methanolic-aqueous media. At moderately high concentration, solutions of PIC in 5 M NaCl/water contain monomers, H-aggregates, and j-aggregates; dye 1 water/methanol solutions consist mostly of monomers and H-aggregates (dimers and higher n-mers); aqueous dye 2 solutions contain only monomers and dimers. Photolysis of H- and/or j-aggregates in PIC and dye 1 cyanine solutions leads to photobleaching of the respective aggregate absorption bands and subsequently decays by biphasic kinetics. Two mechanisms are discussed for the deactivation of excited aggregates. For dye monomers, singlet excited state lifetimes increase (i) with an increase in the length of the aliphatic residues attached to the dye molecule and (ii) with dimerization of the dye molecules. Dimerization restricts torsional dynamics along the dyes polymethine chain and diminishes the nonradiative deactivation channel. An important conclusion from this work is that the thermal energy stored in the aggregates in a short time after picosecond-laser excitation, and the subsequent heating of the surrounding solvent shells, leading to dissolution to smaller aggregates and monomers, provides another pathway to S{sub 1}-S{sub 1} annihilation in the deactivation of excited dye aggregates. 64 refs., 8 figs.

• OSTI ID: 535438
• Journal Information: Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical, Journal Name: Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical Journal Issue: 14 Vol. 101; ISSN 1089-5647; ISSN JPCBFK
• Country of Publication: United States
• Language: English

Related Subjects

40 CHEMISTRY
ABSORPTION SPECTRA
AQUEOUS SOLUTIONS
CYANINE DYES
MONOMERS
PHOTOCHEMISTRY
PHOTOLYSIS
RELAXATION