Limits...
Spectrally resolved photon echo spectroscopy of Zn(II), Co(II) and Ni(II)-octaethyl porphyrins.

Karthick Kumar SK, Tiwari V, Goswami T, Goswami D - Chem Phys Lett (2009)

Bottom Line: Spectrally resolved femtosecond three-pulse photon echo signal from some metal-octaethyl porphyrins (OEPs) like Zn(II)-OEP, Ni(II)-OEP, Co(II)-OEP is reported.Excited state dynamics is studied by time evolving photon echo spectra for different values of coherence and population relaxation times.For all these metallo-porphyrins, the electronic relaxation timescale is found to be limited by our laser pulsewidth of 50 fs whereas the timescale for intramolecular vibrational relaxation, occurring within the Q(00) band was found to be over a picosecond for Co(II)-OEP and Ni(II)-OEP and within a picosecond for Zn(II)-OEP.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, Indian Institute of Technology, Kanpur 208016, India.

ABSTRACT
Spectrally resolved femtosecond three-pulse photon echo signal from some metal-octaethyl porphyrins (OEPs) like Zn(II)-OEP, Ni(II)-OEP, Co(II)-OEP is reported. Excited state dynamics is studied by time evolving photon echo spectra for different values of coherence and population relaxation times. Dependence on the spectrally resolved photon echo spectra on varying metal center is analyzed. For all these metallo-porphyrins, the electronic relaxation timescale is found to be limited by our laser pulsewidth of 50 fs whereas the timescale for intramolecular vibrational relaxation, occurring within the Q(00) band was found to be over a picosecond for Co(II)-OEP and Ni(II)-OEP and within a picosecond for Zn(II)-OEP.

No MeSH data available.


Related in: MedlinePlus

(a) Time-integrated three-pulse photon echo intensities for different samples at t12 = −50 fs. Shown in solid lines are the exponential rise and a bi-exponential decay fits for calculating the associated rise and decay timescales. (b) Time-integrated three-pulse photon echo intensities for different samples at t12 = 0 fs. Shown in solid lines are the exponential rise and a bi-exponential decay fits for calculating the associated rise and decay timescales. (c) Time-integrated three-pulse photon echo intensities for different samples at t12 = +50 fs. Shown in solid lines are the exponential rise and a bi-exponential decay fits for calculating the associated rise and decay timescales.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC2723920&req=5

fig5: (a) Time-integrated three-pulse photon echo intensities for different samples at t12 = −50 fs. Shown in solid lines are the exponential rise and a bi-exponential decay fits for calculating the associated rise and decay timescales. (b) Time-integrated three-pulse photon echo intensities for different samples at t12 = 0 fs. Shown in solid lines are the exponential rise and a bi-exponential decay fits for calculating the associated rise and decay timescales. (c) Time-integrated three-pulse photon echo intensities for different samples at t12 = +50 fs. Shown in solid lines are the exponential rise and a bi-exponential decay fits for calculating the associated rise and decay timescales.

Mentions: Our excitation pulse is in the long wavelength tail of the Q01 band. The time dependent signal is measured as function of delay of the third pulse with respect to the first two pulses that have a fixed delay between them (Fig. 1a). All the three pulses used in our experiment are sub-50 fs and as such, all the sub-50 fs timescales recovered from our experimental measurements is instrument resolution limited. We find the measured signals have a characteristic single exponential sub-50 fs rise followed by a decay that can be effectively fitted to a bi-exponential decay model. If the second pulse arrives 50 fs before the first pulse, the two decay timescales resulting from our bi-exponential decay model are 48 fs and 302 fs for Co(II)–OEP, 44 fs and 100 fs for Ni(II)–OEP and 43 fs and 280 fs for Zn(II)–OEP as shown in Fig. 5a. During zero coherence time, i.e., when the first and the second pulses arrive simultaneously, the two decay terms are respectively, 45 fs and 5 ps for Co(II)–OEP, 46 fs and 1.1 ps for Ni(II)–OEP and 42 fs and 100 fs for Zn(II)–OEP, as shown in Fig. 5b. Finally, when the coherence time is +50 fs, i.e., the second pulse arrives 50 fs after the first pulse, once again two decay terms are seen, which are 43 fs and 1.7 ps for Co(II)–OEP, 42 fs and 1 ps for Ni(II)–OEP and 42 fs and 192 fs for Zn(II)–OEP as shown in Fig. 5c. Thus, in all the cases, the fast component of the bi-exponential decay is also pulsewidth limited (sub-50 fs). The slow component is most prominent for Ni(II)–OEP and least prominent for Zn(II)–OEP. A comparison across the different cases in Fig. 5 shows that Zn-substituted porphyrins behave differently as compared to the Ni or Co substitution, which can perhaps be attributed to the filled d-shell of Zn. Furthermore, in case of Zn porphyrins, π–π interaction is more because of better planarity, as the Zn metal fits more easily into the porphyrin molecule. This can also be one of the reasons why its time constants are much faster than the other metallo-porphyrins. From these timescales we can infer that the ultrafast relaxation of the population placed on Q10 occurs in less than 50 fs and is pulsewidth limited in our case and is related to the Q01 to Q00 electronic relaxation. The longer relaxation timescale associated may be related to the intramolecular vibrational redistribution within the Q00 state.


Spectrally resolved photon echo spectroscopy of Zn(II), Co(II) and Ni(II)-octaethyl porphyrins.

Karthick Kumar SK, Tiwari V, Goswami T, Goswami D - Chem Phys Lett (2009)

(a) Time-integrated three-pulse photon echo intensities for different samples at t12 = −50 fs. Shown in solid lines are the exponential rise and a bi-exponential decay fits for calculating the associated rise and decay timescales. (b) Time-integrated three-pulse photon echo intensities for different samples at t12 = 0 fs. Shown in solid lines are the exponential rise and a bi-exponential decay fits for calculating the associated rise and decay timescales. (c) Time-integrated three-pulse photon echo intensities for different samples at t12 = +50 fs. Shown in solid lines are the exponential rise and a bi-exponential decay fits for calculating the associated rise and decay timescales.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2723920&req=5

fig5: (a) Time-integrated three-pulse photon echo intensities for different samples at t12 = −50 fs. Shown in solid lines are the exponential rise and a bi-exponential decay fits for calculating the associated rise and decay timescales. (b) Time-integrated three-pulse photon echo intensities for different samples at t12 = 0 fs. Shown in solid lines are the exponential rise and a bi-exponential decay fits for calculating the associated rise and decay timescales. (c) Time-integrated three-pulse photon echo intensities for different samples at t12 = +50 fs. Shown in solid lines are the exponential rise and a bi-exponential decay fits for calculating the associated rise and decay timescales.
Mentions: Our excitation pulse is in the long wavelength tail of the Q01 band. The time dependent signal is measured as function of delay of the third pulse with respect to the first two pulses that have a fixed delay between them (Fig. 1a). All the three pulses used in our experiment are sub-50 fs and as such, all the sub-50 fs timescales recovered from our experimental measurements is instrument resolution limited. We find the measured signals have a characteristic single exponential sub-50 fs rise followed by a decay that can be effectively fitted to a bi-exponential decay model. If the second pulse arrives 50 fs before the first pulse, the two decay timescales resulting from our bi-exponential decay model are 48 fs and 302 fs for Co(II)–OEP, 44 fs and 100 fs for Ni(II)–OEP and 43 fs and 280 fs for Zn(II)–OEP as shown in Fig. 5a. During zero coherence time, i.e., when the first and the second pulses arrive simultaneously, the two decay terms are respectively, 45 fs and 5 ps for Co(II)–OEP, 46 fs and 1.1 ps for Ni(II)–OEP and 42 fs and 100 fs for Zn(II)–OEP, as shown in Fig. 5b. Finally, when the coherence time is +50 fs, i.e., the second pulse arrives 50 fs after the first pulse, once again two decay terms are seen, which are 43 fs and 1.7 ps for Co(II)–OEP, 42 fs and 1 ps for Ni(II)–OEP and 42 fs and 192 fs for Zn(II)–OEP as shown in Fig. 5c. Thus, in all the cases, the fast component of the bi-exponential decay is also pulsewidth limited (sub-50 fs). The slow component is most prominent for Ni(II)–OEP and least prominent for Zn(II)–OEP. A comparison across the different cases in Fig. 5 shows that Zn-substituted porphyrins behave differently as compared to the Ni or Co substitution, which can perhaps be attributed to the filled d-shell of Zn. Furthermore, in case of Zn porphyrins, π–π interaction is more because of better planarity, as the Zn metal fits more easily into the porphyrin molecule. This can also be one of the reasons why its time constants are much faster than the other metallo-porphyrins. From these timescales we can infer that the ultrafast relaxation of the population placed on Q10 occurs in less than 50 fs and is pulsewidth limited in our case and is related to the Q01 to Q00 electronic relaxation. The longer relaxation timescale associated may be related to the intramolecular vibrational redistribution within the Q00 state.

Bottom Line: Spectrally resolved femtosecond three-pulse photon echo signal from some metal-octaethyl porphyrins (OEPs) like Zn(II)-OEP, Ni(II)-OEP, Co(II)-OEP is reported.Excited state dynamics is studied by time evolving photon echo spectra for different values of coherence and population relaxation times.For all these metallo-porphyrins, the electronic relaxation timescale is found to be limited by our laser pulsewidth of 50 fs whereas the timescale for intramolecular vibrational relaxation, occurring within the Q(00) band was found to be over a picosecond for Co(II)-OEP and Ni(II)-OEP and within a picosecond for Zn(II)-OEP.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, Indian Institute of Technology, Kanpur 208016, India.

ABSTRACT
Spectrally resolved femtosecond three-pulse photon echo signal from some metal-octaethyl porphyrins (OEPs) like Zn(II)-OEP, Ni(II)-OEP, Co(II)-OEP is reported. Excited state dynamics is studied by time evolving photon echo spectra for different values of coherence and population relaxation times. Dependence on the spectrally resolved photon echo spectra on varying metal center is analyzed. For all these metallo-porphyrins, the electronic relaxation timescale is found to be limited by our laser pulsewidth of 50 fs whereas the timescale for intramolecular vibrational relaxation, occurring within the Q(00) band was found to be over a picosecond for Co(II)-OEP and Ni(II)-OEP and within a picosecond for Zn(II)-OEP.

No MeSH data available.


Related in: MedlinePlus