Please use this identifier to cite or link to this item: http://hdl.handle.net/10397/24003
Title: Ligand pi-conjugation dictated intersystem crossing in phenyleneethynylene gold(I) complexes
Authors: Ma, C
Chan, CTL
Kwok, WM 
Che, CM
Issue Date: 2012
Publisher: Royal Soc Chemistry
Source: Chemical science, 2012, v. 3, no. 6, p. 1883-1892 How to cite?
Journal: Chemical Science 
Abstract: The excited state dynamics of gold(I) complexes containing monomeric phenyleneethynylene (PE) or oligo (p- or m-PE) ligand, namely PhC CAu(PCy3) (1a) and PhC C(C6H4-1,m-C C)(2)Au(PCy3) (m = 4, 2a; m = 3, 3a) were investigated by combined methods of femtosecond transient absorption (fs-TA), fs time-resolved fluorescence (fs-TRF) and nanosecond time-resolved emission (ns-TRE). Comparative study was also performed on the corresponding metal free p- and m-PE oligomers (2b and 3b) to allow for evaluating the effect of ligand pi-conjugation and the effect of gold(I) on the overall dynamics and emission pathways of the gold(I)-PE complexes. The results reveal that, although the incorporation of heavy gold(I) into PE ligand is effective in promoting the spin-forbidden ligand centered S-1(1)pi pi* to T-1(3)pi pi* intersystem crossing (ISC), the exact ISC rate constant (k(ISC)) is largely controlled by p-conjugation of the PE ligand in the S-1 states of 1a-3a. Upon increasing pi-conjugation as from 1a to 3a and to 2a, the k(ISC) decreases consecutively by similar to 2 orders of magnitude from similar to 1.2 x 10(12) s(-1) in 1a to similar to 2.6 x 10(10) and similar to 1.6 x 10(8) s(-1) in 3a and 2a, respectively. As a result, the prompt fluorescence (PF) from the initial S-1(1)pi pi* state is quenched to markedly different extent, with the lifetime (tau(PF)) ranging from similar to 0.7 ps in 1a to similar to 450 ps in 2a. Aside from PF, long-lived delayed fluorescence (DF, lifetime on microsecond timescale) formed due to triplet-triplet annihilation (TTA) has also been identified to contribute to the fluorescence of 2a and 3a but not 1a. The ligand dependent behavior of both the k(ISC) and DF provides a rationale to the varied efficiency and unusual composition of the emissions of 1a-3a. The findings present a compelling case that impacts the conventional scenario of ISC due to the heavy-atom effect in the excited state decay of transition-metal complexes; the photophysical parameters and the deactivation pattern derived in this work are useful information for understanding the structure-property relationship of transition-metal-PE complexes.
URI: http://hdl.handle.net/10397/24003
ISSN: 2041-6520
DOI: 10.1039/c2sc20038d
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