Energy Relaxation Dynamics of Excited Triplet States of Directly Linked Zn(II)Porphyrin Arrays

Song, Nam Woong; Cho, Hyun Sun; Yoon, Min Chul; Aratani, Naoki; Osuka, Atsuhiro; Kim, Dongho

doi:10.5012/bkcs.2002.23.2.271

Cited by 14 publications

(4 citation statements)

References 28 publications

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“…Notably, the contribution of the shorter decay component (44%) when using 580 nm as a pump is greater than that when using 620 nm (22%). Similar to that observed in the femtosecond TA spectra, strong GSB and ESA signals are also shown for both PF26H and PF28H in the nanosecond TA experiments . At 293 K, the lifetime of the T 1 state of PF26H is determined to be ∼4.8 μs, whereas that of PF28H cannot be determined, supposedly due to a short T 1 -state lifetime within the instrument response time of 100 ns.…”

Section: Control Of Aromaticity By Regulating the Temperaturesupporting

confidence: 79%

Control and Switching of Aromaticity in Various All-Aza-Expanded Porphyrins: Spectroscopic and Theoretical Analyses

et al. 2016

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Modification of aromaticity is regarded as one of the most interesting and important research topics in the field of physical organic chemistry. Particularly, porphyrins and their analogues (porphyrinoids) are attractive molecules for exploring various types of aromaticity because most porphyrinoids exhibit circular conjugation pathways in their macrocyclic rings with various molecular structures. Aromaticity in porphyrinoids is significantly affected by structural modification, redox chemistry, NH tautomerization, and electronic states (singlet and triplet excited states). Conversely, aromaticity significantly affects the spectroscopic properties and chemical reactivities of porphyrinoids. In this context, considerable efforts have been devoted to understanding and controlling the aromaticity and antiaromaticity of porphyrinoids. Thus, a series of porphyrinoids are in the limelight, being expected to shed light on this field because they have some advantages to demonstrate the switching of aromaticity; it is possible to control the aromaticity by lowering the temperature, adding and removing the protons of expanded porphyrins, changing the chemical environment, and switching the electronic states (triplet and singlet excited states) by photoexcitation. In this regard, this Review describes the control of aromaticity in various expanded porphyrins from the spectroscopic point of view with assistance from theoretical calculations.

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Section: Control Of Aromaticity By Regulating the Temperaturesupporting

confidence: 79%

Control and Switching of Aromaticity in Various All-Aza-Expanded Porphyrins: Spectroscopic and Theoretical Analyses

et al. 2016

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“…In the NIR region from 700 to 1000 nm, no typical spectral structures have been observed for both Z1 and Z2 within a delay time of a few hundred picoseconds. After a long delay time of nanoseconds, however, a pronounced photoinduced absorption band appears at around 800 nm, of which spectral features as well as its dynamics have been well-known to be characteristic of porphyrin triplet−triplet absorption 6 Transient absorption spectra of Z1 (top), S2 (middle), and Z2 (bottom) at three time delays after photoexcitation at 400 nm (left).…”

Section: Resultsmentioning

confidence: 99%

Comparative Studies on Energy Relaxation Dynamics of Directly Linked Zn^II Porphyrin Dimers with Different Dihedral Angles

Cho

Song

et al. 2003

J. Phys. Chem. A

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Photophysical properties of the strapped Zn II porphyrin dimers (Sn, the strap chain between the porphyrins changes; -O-(CH 2 ) n -O-, n ) 1, 2, 3, 4, 8, and 10) and directly linked Zn II porphyrin dimer (Z2) have been investigated by the steady-state and time-resolved spectroscopic methods. The reduced dihedral angle in Sn gives rise to additional absorption bands around 400 nm as well as broad fluorescence in the nearinfrared region. The fluorescence lifetimes of Sn become gradually, but not so significantly, shorter as the strap length becomes shorter, indicating that the lifetimes of the lowest excited singlet states of Sn are not affected much despite their structural distortions such as mean plane deviations and the existence of two conformers. Fluorescence excitation and viscosity-dependent fluorescence spectra suggest that S2 exists as two conformers, A and B conformer, which has been also confirmed by X-ray data. The B conformer with a shorter interporphyrin distance has stronger interporphyrin interactions than the A conformer, which was revealed by the fluorescence excitation and fluorescence spectra. The A conformer is responsible for the shorter wavelength fluorescence at ca. 660 nm, whereas the B conformer gives rise to the near-infrared fluorescence. The photoinduced near-infrared absorption band was suggested to be characteristic of S2, which was not observed in Z2. The conformational dynamics of S2 with a time constant of 15 ps was observed in the transient absorption and fluorescence upconversion measurements. From the comparative studies of Z2 and Sn, we have demonstrated that the orientation of the two porphyrin macrocycles has a considerable effect on their photophysical properties.

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“…Nanosecond Flash Photolysis Measurements. The nanosecond transient absorption spectra were obtained by nanosecond flash photolysis technique . An excitation pulse of 532 nm was generated from the second harmonic output of a Q-switched Nd:YAG laser (Continuum, Surelite).…”

Section: Methodsmentioning

confidence: 99%

Comparative Photophysics of [26]- and [28]Hexaphyrins(1.1.1.1.1.1): Large Two-Photon Absorption Cross Section of Aromatic [26]Hexaphyrins(1.1.1.1.1.1)

et al. 2005

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We have explored the electronic natures of representative expanded porphyrins, [26]- and [28]hexaphyrins, to investigate the interplay between the aromaticity and antiaromaticity that is brought by two electron oxidation/reduction processes. The excited singlet and triplet states of [26]hexaphyrin in solution exhibit lifetimes of 125 ps and 1.8 mus, respectively, as revealed by various time-resolved spectroscopic measurements. On the other hand, [28]hexaphyrin shows faster singlet and triplet lifetimes than those of [26]hexaphyrin, which is largely in accordance with the perturbation of aromaticity due to the pi electron formulation of [4n] in [28]hexaphyrins. The two-photon absorption cross-section values at 1200 nm for [26]hexaphyrins show ca. 9890 GM which is >10(2) larger than those of porphyrins. The reduced TPA values of 2600 and 810 GM of [28]hexaphyrin and perfluorinated [28]hexaphyrin, respectively, match well with their relatively short excited-state lifetimes. Overall, the enhanced excited-state lifetimes for various hexaphyrins go in line with the increased TPA cross-section values and the ring planarity.

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Energy Relaxation Dynamics of Excited Triplet States of Directly Linked Zn(II)Porphyrin Arrays

Cited by 14 publications

References 28 publications

Control and Switching of Aromaticity in Various All-Aza-Expanded Porphyrins: Spectroscopic and Theoretical Analyses

Control and Switching of Aromaticity in Various All-Aza-Expanded Porphyrins: Spectroscopic and Theoretical Analyses

Comparative Studies on Energy Relaxation Dynamics of Directly Linked Zn^II Porphyrin Dimers with Different Dihedral Angles

Comparative Photophysics of [26]- and [28]Hexaphyrins(1.1.1.1.1.1): Large Two-Photon Absorption Cross Section of Aromatic [26]Hexaphyrins(1.1.1.1.1.1)

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Energy Relaxation Dynamics of Excited Triplet States of Directly Linked Zn(II)Porphyrin Arrays

Cited by 14 publications

References 28 publications

Control and Switching of Aromaticity in Various All-Aza-Expanded Porphyrins: Spectroscopic and Theoretical Analyses

Control and Switching of Aromaticity in Various All-Aza-Expanded Porphyrins: Spectroscopic and Theoretical Analyses

Comparative Studies on Energy Relaxation Dynamics of Directly Linked ZnII Porphyrin Dimers with Different Dihedral Angles

Comparative Photophysics of [26]- and [28]Hexaphyrins(1.1.1.1.1.1): Large Two-Photon Absorption Cross Section of Aromatic [26]Hexaphyrins(1.1.1.1.1.1)

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Comparative Studies on Energy Relaxation Dynamics of Directly Linked Zn^II Porphyrin Dimers with Different Dihedral Angles