Excited-state absorption of a bipyridyl platinum(II) complex with alkynyl-benzothiazolylfluorene units

Abstract

The singlet excited-state lifetime of a bipyridyl platinum(II) complex containing two alkynyl-benzothiazolylfluorene units was determined to be 145+/-105 ps by fitting femtosecond transient difference absorption data, and the triplet quantum yield was measured to be 0.14. A ground-state absorption cross section of 6.1 x 10(-19) cm(2) at 532 nm was deduced from UV-visible absorption data. Excited-state absorption cross sections of (6.7+/-0.1) x 10(-17) cm(2) (singlet) and (4.6+/-0.1) x 10(-16) cm(2) (triplet) were obtained by using a five-level dynamic model to fit open-aperture Z scans at picosecond and nanosecond pulse widths and a variety of pulse energies. For this complex, the ratio of the triplet excited-state absorption cross section to the ground-state absorption cross section--long used as a figure of merit for reverse saturable absorbers--thus stands at 754, to our knowledge the largest ever reported at 532 nm wavelength.

Long-lifetime reverse saturable absorption in a bipyridyl platinum(II) complex bearing naphthalimidylethynyl-substituted fluorenylacetylide ligands

“…However, this large reported value of the cross-section ratio reflects not the strength of the latter complex's triplet excited-state absorption, but rather the weakness of its ground-state absorption at 532 nm resulting from the negative solvatochromic effect of the dichloromethane solvent. Indeed, the value of r T (532 nm) reported here for bpyPt(C"CAFAC"CANI) 2 in toluene, 7.8 Â 10 -16 cm 2 , is significantly larger than that reported in [16] for bpyPt(C"CAFABTZ) 2 in dichloromethane, 4.6 Â 10 -16 cm 2 . In toluene, where bpyPt(C"CAFABTZ) 2 exhibits a measured r G (532 nm) of 9.6 Â 10 -18 cm 2 , one would expect the ratio r T (532 nm)/r G (532 nm) to be comparable for the two complexes.…”

“…We report the following photophysical parameter values for bpyPt(C"CAFAC"CANI) 2 The ratio of absorption cross sections r T (532 nm)/r G (532 nm) for bpyPt(C"CAFAC"CANI) 2 in toluene is only 66, compared to the value of 754 reported in [16] for bpyPt(C"CAFABTZ) 2 in dichloromethane, a more polar solvent. However, this large reported value of the cross-section ratio reflects not the strength of the latter complex's triplet excited-state absorption, but rather the weakness of its ground-state absorption at 532 nm resulting from the negative solvatochromic effect of the dichloromethane solvent.…”

“…Now, the molecule whose photophysical parameters were reported in [16,9] a 4,4 0 -di-tert-butyl-2,2 0 -bipyridyl platinum(II) complex bearing a pair of 2-(benzothiazol-2 0 -yl)-7-ethynyl-9,9-diethylfluorenyl ligands, exhibits one of the largest values of the cross-section ratio r T (532 nm)/r G (532 nm) ever reported, but it has a triplet excitedstate lifetime s T of only $800 ns in deoxygenated toluene solution.…”

Broadband Nonlinear Absorbing Platinum 2,2′-Bipyridine Complex Bearing 2-(Benzothiazol-2′-yl)-9,9-diethyl-7-ethynylfluorene Ligands

“…The various photophysical parameters that appear in the model were determined from independent measurements: values of the ground-state absorption cross section σ 0 (λ) were obtained from the UV-vis absorption spectrum; the singlet excited-state lifetime, from the decay of the femtosecond TA; the triplet excited state lifetime, from the decay of nanosecond TA; the triplet quantum yield, from the relative actinometry; and the effective triplet-triplet excited-state absorption cross section σ T (λ) was deduced from the femtosecond TA curve at 5.8 ns time delay in combination with the value of σ T at 532 nm, 4.6 Â 10 -16 cm 2 , which itself was determined from combined fitting of nanosecond and picosecond Z-scan data. 10 Detailed descriptions of the model and the fitting process have been reported by our group previously. 19 Figure 5 shows representative Z scan experimental data and fitting curves for 1 at 532 and 760 nm at a series of different excitation energies.…”

Strong triplet excited-state absorption in a phenanthrolinyl iridium(III) complex with benzothiazolylfluorenyl-substituted ligands

“…Because the triplet yield of phen-Irppy-BTF 2 is so small, it may be more realistic to consider the alternative figure of merit Φσ T λ∕σ G λ, whose value at 532 nm for phen-Irppy-BTF 2 in toluene is still, at 500, one of the largest ever reported. For purposes of comparison, the value of Φσ T 532 nm∕σ G (532 nm) is only 23 for lead tetra-tert-butyl phthalocyanine (triplet yield 0.98) [7] and only 106 for bpy-PtC ≡ C − BTF 2 , the platinum(II) 2; 2 0 -bipyridine with benzothiazolylethynylfluorenyl ligands whose photophysical parameters were first reported in [27]. …”