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Synchronously pumped dye lasers in fluorescence decay measurements of molecular motion
128 Picosecond spectroscopyof some metalloporphyrius K.D.
STRAUB
VA Medicul Center and UA Medical School, 300 E. Rooseveli Road, Little Rock, AR 72204 (U.S.A.) D. HUPPERT Department
of Chemistry, Tel Aviv University, Tel Aviv 69978 (Israel)
P. M . RENTZEPIS Bell Laboratories, Murray Hill, NJ 07974 (U.S.A.)
The energy relaxation process of metal-free protoporphyrin IX dimethyl ester and its compounds with Cu(II), Ag(II), Ni(II), Pd(II), Pt(II), Zn(II), Fe(II1) and the heme proteins myoglobin, hemoglobin and cytochrome c were studied by dual-beam picosecond spectroscopy. Excitation at 530 nm, which is in the fl visible absorption band for these compounds, revealed that both the metal-free porphyrin and the Zn(I1) porphyrin have lifetimes for S, which are longer than 1 ns, in keeping with their known fluorescence properties. From the time-resolved spectra after excitation, absorption due to S1, T, and So could be identified. In addition, a low-lying singlet d4 level was seen for the Ni(I1) porphyrin. While the Pt(I1) and Pd(I1) compounds have intersystem crossing times of less than 8 ps and 20 ps respectively, the Ni(I1) compound relaxes from S1 to Sd in about 10 ps and from Sd to So in 260 ps. The paramagnetic Cu(I1) and Ag(I1) species have intersystem crossing from ‘S1 to 2T1 in less than 8 ps followed by an equilibrium of the 2T1 and 4T1 states, requiring about 450 ps for the Cu(I1) compound and about 12 ps for the Ag(I1) compound. An anomalous lengthening of the decay time with increasing excitation intensity was observed for the copper but not for the silver porphyrin. The Fe(II1) porphyrins relax with rates faster than 6 ps, which was the resolving time of this experiment. No differences between heme proteins and Fe(II1) protoporphyrins in solution were observable within this time resolution.
Syuchronouslypumped dye lasers iu fluorescencedecay measurementsof molecular motion G. BEDDARD,
T. DOUST,
S.R. MEECH
and D. PHILLIPS
The Royal Institution, 21 Albemarle Street, London WI X 4BS (Gt Britain)
The advent of stable and reliable synchronously pumped dye laser systems has greatly improved the measurement of fluorescence decay times in both the picosecond and the nanosecond time domains. When used in conjunction with
129 time-correlated single-photon counting techniques, the enhanced signal-to-noise ratio permits analysis of multicomponent fluorescence such as is obtained in many heterogeneous systems. Examples of this type of analysis are given with particular reference to macromolecular excimer-formmg systems in comparison with the analogous free molecules in solution. For picosecond measurements the nonlinear phenomenon of sum frequency generation in anisotropic crystals offers several advantages over single-photon counting techniques. These include improved time resolution, the ability to detect fluorescence in the far red and IR without resort to special red-sensitive photodetectors and measurement of fluorescence anisotropy. Examples are given of rotational diffusion measurements tin the dyes cresyl violet and oxazine.
Picosecond fluorescence spechoscopy of N-vinyl carbazole polymers
K.P. GHIGGINO
and
P.F. SKILTON
Department of Physical Chemistry, University of Melbuurne, Parkville, Victoria 3052 (Australia)
Energy migration and excimer formation in poly(N-vinyl carbazole) and various copolymers of N-vinyl carbazole were studied as a function of solvent and temperature using both steady state and picosemnd fluorescence spectroscopy. In dilute dichloromethane solutions, emission from the polymers may be attributed to fluorescence from initially excited carbazole chromophores and two distinct excimer sites with emission maxima at 370 and 420 nm. The relative contribution to emission from monomeric species D1 and Dz is markedly dependent on the copolymer composition. Picosecond fluorescence measurements and temperature dependence studies indicate that rapid energy migration to preformed sites along the polymer chain is the major mechanism for populating the excimer sites in the homopolymer. However, in certain copolymers there is evidence for excimer formation by slower main chain rotation and side group motion during the excited state lifetime_ With methyl tetrahydrofuran as the solvent the number and fluorescence properties of the excimer species are significantly altered. These observations may be explained by appropriate kinetic schemes which take into account the effects of molecular structure and solvent on the conformation and excited state relaxation pathways of N-vinyl carbazole polymers.
STRAUB
VA Medicul Center and UA Medical School, 300 E. Rooseveli Road, Little Rock, AR 72204 (U.S.A.) D. HUPPERT Department
of Chemistry, Tel Aviv University, Tel Aviv 69978 (Israel)
P. M . RENTZEPIS Bell Laboratories, Murray Hill, NJ 07974 (U.S.A.)
The energy relaxation process of metal-free protoporphyrin IX dimethyl ester and its compounds with Cu(II), Ag(II), Ni(II), Pd(II), Pt(II), Zn(II), Fe(II1) and the heme proteins myoglobin, hemoglobin and cytochrome c were studied by dual-beam picosecond spectroscopy. Excitation at 530 nm, which is in the fl visible absorption band for these compounds, revealed that both the metal-free porphyrin and the Zn(I1) porphyrin have lifetimes for S, which are longer than 1 ns, in keeping with their known fluorescence properties. From the time-resolved spectra after excitation, absorption due to S1, T, and So could be identified. In addition, a low-lying singlet d4 level was seen for the Ni(I1) porphyrin. While the Pt(I1) and Pd(I1) compounds have intersystem crossing times of less than 8 ps and 20 ps respectively, the Ni(I1) compound relaxes from S1 to Sd in about 10 ps and from Sd to So in 260 ps. The paramagnetic Cu(I1) and Ag(I1) species have intersystem crossing from ‘S1 to 2T1 in less than 8 ps followed by an equilibrium of the 2T1 and 4T1 states, requiring about 450 ps for the Cu(I1) compound and about 12 ps for the Ag(I1) compound. An anomalous lengthening of the decay time with increasing excitation intensity was observed for the copper but not for the silver porphyrin. The Fe(II1) porphyrins relax with rates faster than 6 ps, which was the resolving time of this experiment. No differences between heme proteins and Fe(II1) protoporphyrins in solution were observable within this time resolution.
Syuchronouslypumped dye lasers iu fluorescencedecay measurementsof molecular motion G. BEDDARD,
T. DOUST,
S.R. MEECH
and D. PHILLIPS
The Royal Institution, 21 Albemarle Street, London WI X 4BS (Gt Britain)
The advent of stable and reliable synchronously pumped dye laser systems has greatly improved the measurement of fluorescence decay times in both the picosecond and the nanosecond time domains. When used in conjunction with
129 time-correlated single-photon counting techniques, the enhanced signal-to-noise ratio permits analysis of multicomponent fluorescence such as is obtained in many heterogeneous systems. Examples of this type of analysis are given with particular reference to macromolecular excimer-formmg systems in comparison with the analogous free molecules in solution. For picosecond measurements the nonlinear phenomenon of sum frequency generation in anisotropic crystals offers several advantages over single-photon counting techniques. These include improved time resolution, the ability to detect fluorescence in the far red and IR without resort to special red-sensitive photodetectors and measurement of fluorescence anisotropy. Examples are given of rotational diffusion measurements tin the dyes cresyl violet and oxazine.
Picosecond fluorescence spechoscopy of N-vinyl carbazole polymers
K.P. GHIGGINO
and
P.F. SKILTON
Department of Physical Chemistry, University of Melbuurne, Parkville, Victoria 3052 (Australia)
Energy migration and excimer formation in poly(N-vinyl carbazole) and various copolymers of N-vinyl carbazole were studied as a function of solvent and temperature using both steady state and picosemnd fluorescence spectroscopy. In dilute dichloromethane solutions, emission from the polymers may be attributed to fluorescence from initially excited carbazole chromophores and two distinct excimer sites with emission maxima at 370 and 420 nm. The relative contribution to emission from monomeric species D1 and Dz is markedly dependent on the copolymer composition. Picosecond fluorescence measurements and temperature dependence studies indicate that rapid energy migration to preformed sites along the polymer chain is the major mechanism for populating the excimer sites in the homopolymer. However, in certain copolymers there is evidence for excimer formation by slower main chain rotation and side group motion during the excited state lifetime_ With methyl tetrahydrofuran as the solvent the number and fluorescence properties of the excimer species are significantly altered. These observations may be explained by appropriate kinetic schemes which take into account the effects of molecular structure and solvent on the conformation and excited state relaxation pathways of N-vinyl carbazole polymers.