The photophysics of fac-[Re(CO)3(dppz)(py)]+ in CH3CN: a comparative picosecond flash photolysis, transient infrared, transient resonance Raman and density functional theoretical study

Abstract

The photophysical properties of fac-[Re(CO)3(dppz)(py)]+ (1, where dppz = dipyrido[3,2-a: 2',3'-c]phenazine) in CH3CN have been investigated using a series of complementary techniques including visible and infrared transient absorption and resonance Raman spectroscopy on the picosecond and nanosecond timescales. The results confirm previous reports that the lowest-lying emissive state in 1 is a triplet intra-ligand (3IL) state localised on the dppz ligand and have provided detailed information on the dynamics of 1 upon photoexcitation, including the relative energies of the excited state species encountered and the electronic distribution within these. If the dppz ligand is viewed in terms of phenanthroline (phen) and phenazine (phz) moieties, the emissive state is probably more accurately described as a 3 pi-->pi *(phz) IL state. The picosecond studies have shown that this emissive state is formed, at least in part, within 30 ps of excitation from a precursor, which is possibly a 3 pi-->pi *(phen) IL state. On the nanosecond timescale, TRIR has been employed to elucidate further dynamics and reveal the presence of an energetically close-lying state in equilibrium with the emissive state. This has tentatively been assigned as being 3d pi(Re)-->pi *(phz) metal-to-ligand charge transfer (MLCT) in nature. A summary of the photophysics is proposed in the form of a Jablonski scheme. Time dependent density functional theory (TD-DFT) calculations support the relative ordering and suggested electronic character of the excited state species involved.

Charge Photoinjection in Intercalated and Covalently Bound [Re(CO)3(dppz)(py)]+–DNA Constructs Monitored by Time-Resolved Visible and Infrared Spectroscopy

“…The down-shift in the energies of the transient bands from the ground-state positions is typical of ππ* 3 IL(dppz) excited states. 19–23,26,27,54 Tentatively, we attribute the initially formed 2026 and 1908 cm −1 transient bands to a hot 3 IL state localized at the phen part of the dppz ligand, 3 IL(phen). Subsequent electron density reorganization and cooling produce another 3 IL state localized predominantly at the phenazine part, 3 IL(phz), manifested as the sharp 2036 cm −1 band.…”

“…In the absence of DNA, negligible emission is observed from an aqueous solution of Re′-OH or Re′-OEt; however, in the presence of AT-30 and in the Re-25(I) sample, a prominent emission band is observed that exhibits a maximum at 570 nm and a shoulder near 600 nm, resembling the emission spectrum seen for similar Re complexes in organic solvents. 19,21,22,41,42,57,65 By comparison with the emission of [Ru(bpy) 3 ] 2+ in deaerated acetonitrile, the emission quantum yield of Re′-OEt in the presence of AT-30 in buffer is 0.008 (compared to 0.062 for [Ru(bpy) 3 ] 2+ ). 73 In the presence of GC-30 and in the Re-25(G) sample, the emission is much less intense, the maxima are shifted to 585 nm, and no shoulder is observed.…”

“…Emission is expected to occur primarily from the 3 IL state, as reported for [Re(CO) 3 (dppz)(py)] + in acetonitrile. 19 In the second population, the excited complex is well coupled to the DNA. Here, excited state quenching via positive charge ( i.e.…”

Ultrafast Excited State Dynamics Controlling Photochemical Isomerization of N‐Methyl‐4‐[trans‐2‐(4‐pyridyl)ethenyl]pyridinium Coordinated to a {ReI(CO)3(2,2′‐bipyridine)} Chromophore

“…[1] Re I carbonyl diimine complexes are mostly photostable and suitable as sensors or switches. [4,[8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] In rare cases, [23,24] some of which will be discussed below, the lowest excited state is localized on the ligand X and isomerization may ensue after its population.…”

Probing the excited state nature of coordination complexes with blended organic and inorganic chromophores using vibrational spectroscopy

“…[92] The nature of the lowest excited states of several dppz-complexes have been identified using TRIR spectroscopy on the picosecond timescale. [40][41][42][43][44][45][46][47]93] American Chemical Society.…”