Intermolecular interaction of photoexcited Cu(TMpy-P4) with water studied by transient resonance Raman and picosecond absorption spectroscopies

Abstract

A photoinduced complex between Cu(TMpy-P4) and water molecules, reversibly axially coordinated to the central metal, was observed in picosecond transient absorption and nanosecond resonance Raman experiments. This complex is rapidly created (z~ = 15 + 5 ps) in the excited triplet (~r, ~r * ) state of Cu-porphyrin, and the subsequent relaxation is proposed to proceed via two parallel pathways. One is fast and efficient (>/90% of molecules), and presumably involves a (ax, d) charge-transfer state. The second pathway is slow (z 2 >> 1 ns), has a low quantum yield (~< 10%) and involves the excited (d, d) state which is responsible for transient Raman features at = 1553 cm -I (u2*) and = 1347 cm -1 (u4*), and for low-intensity long-lived transient absorption features.

Design and Photophysical Properties of Zinc(II) Porphyrin‐Containing Dendrons Linked to a Central Artificial Special Pair

“…Because of the efficient triplet formation, investigations of this excited state revealed the presence of many triplet state phenomena, such as the presence of a lower-energy charge-transfer state (ring!metal) operating on the ps timescale, [29] the formation of an exciplex with water (among other donors) [30] also being formed on the ps timescale ((15 AE 5) ps), [31] the formation of singlet oxygen (see, for example, ref. [32]), the T 1 -T 1 energy transfers to free bases, [33] and enhancement of intersystem crossing by through-bond exchange interactions.…”

Photoprocesses of Copper Complexes That Bind to DNA

“…1 ns. 107 They assigned the transient Raman signals to the latter component which they identified as a d-d excited state with an axially bound water. They rationalized the low yield (φ e 0.1) of the d-d excited-state adduct in terms of competitive deactivation via a five-coordinate CT state.…”

“…A subsequent paper by Kruglik et al reported that the exciplex involving a bound water molecule forms in low yield and has a lifetime in excess of a nanosecond. 107 They also concluded that the adduct exhibits a distinctive blue shift in its Soret band.…”

Excited States of Water-Soluble Metal Porphyrins as Microenvironmental Probes for DNA and DNA-Model Compounds: Time-Resolved Transient Absorption and Resonance Raman Studies of Ni(TMpy-P4) in [Poly(dG-dC)]2and [Poly(dA-dT)]2

“…RR spectra were recorded several times, independently at three different nanosecond Raman spectrometers available in our laboratories in Minsk, 22 Paris, 26 and Enschede. 53 All systems were based on Q-switched Nd:YAG lasers, used as pump source for other laser devices such as dye lasers, Raman shifters, and frequency mixers. All Raman spectra were collected in using nearly backscattering geometries.…”

“…Raman scattering signal was dispersed either by a double diffraction DFS-52 22 and Jobin-Yvon HG2S 26 monochromator (in the case of single-channel detection system) or by the Spex Triplemate 1877 polychromator in combination with a PAR-1421 multichannel array detector. 53 Spectral resolution in all experiments was typically ca. 5-7 cm -1 .…”