Interaction of electronically excited copper(II)-porphyrin with oligo- and polynucleotides: exciplex building process by photoinitiated axial ligation of porphyrin to thymine and uracil residues

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

“…2 presents RR spectra of Cu(TMpy-P4) in PBS. Spectrum 2C was recorded with cw excitation at 413 nm from a Kr + laser: it is consistent with published data [6,7,14]. The transient RR spectra in Fig.…”

“…2A, B). Indeed, analysis of Table 1 shows that for Cu(TMpy-P4) in PBS, the ~'2" and ~'4" bands exhibit the same 20 cm-~ downshifts as found in earlier studies of the (d, d)-state species of 5-coordinate Cu(TMpy-P4) complexed with poly(dA-dT) [7,8] and of CuTPP in 1552 1366 1348 CuTPP in THF [5] 1565 1543 1366 1342 CuTPP in dioxane [5] 1564 1544 1366 1344 THF or dioxane [5]. Another probable candidate for the long-lived transient species would be a non-stationary 5-coordinate ground-state complex [CUP-H20].…”

“…[5] that the binding of axial ligands by CuP in the ground electronic state leads to only a weak perturbation of the porphyrin structure, reflected in small frequency shifts, i.e. lower than 10 cm -L. Moreover, we note that the Raman intensity patterns for the excited-state bands are remarkably different: in the latter case the exciplex bands are equal to or even more intense than the ground-state bands at high excitation power [5,7,8], while for CuP-H20, the transient bands are much less pronounced and appear as shoulders on the ground-state contours (Fig. 2).…”

“…shielded from water molecules). Taking this into account, along with our previous studies of the photoinduced interaction between CuP and various O-containing molecules [4][5][6][7][8], it is assumed that the photoexcitation of CuP increases its affinity for axial ligands so that binding of a water molecule as a fifth (axial) ligand to the Cu(II) central ion of Cu(TMpy-P4) in its triplet (w, ~r * ) state is responsible for the observed triplet-state quenching. The diffusion-controlled mechanism of water binding is supported by the results of an experiment in which an increase in solvent viscosity (by adding glycerol in a 1:1 (v:v) proportion) results in an increase in the triplet-state lifetime up to 60 ps: this slows the diffusion and rotation movements of free water molecules necessary for a proper encounter with the central copper ion of the excited porphyrin.…”

“…In particular, a vacancy in the upper d(x2-y 2) orbital results in a bigger affinity of excited CuP for nitrogen (N)-and oxygen (O)-containing molecules from the environment, whose con- ' Corresponding author. sequence is a possible reversible binding of these molecules to the central copper ion as a fifth axial ligand [2][3][4][5][6][7][8][9][10]. It has recently been reported that the excited triplet (~, "rr *) state (T I) of the water-soluble cationic Cu(II) derivative of 5,10,15,20-tetrakis[4-N-methylpyridyl]porphyrin (Cu(TMpy-P4)) has a short lifetime of ca.…”