Photoinduced Processes in Rhenium(I) Terpyridine Complexes Bearing Remote Amine Groups: New Insights from Transient Absorption Spectroscopy

Abstract

Photophysical properties of two Re(I) complexes [ReCl(CO)3(R-C6H4-terpy-κ2N)] with remote amine groups, N-methyl-piperazinyl (1) and (2-cyanoethyl)methylamine (2), were investigated. The complexes show strong absorption in the visible region corresponding to metal-to-ligand charge transfer (1MLCT) and intraligand-charge-transfer (1ILCT) transitions. The energy levels of 3MLCT and 3ILCT excited-states, and thus photoluminescence properties of 1 and 2, were found to be strongly affected by the solvent polarity. Compared to the parent chromophore [ReCl(CO)3(C6H5-terpy-κ2N)] (3), both designed complexes show significantly prolonged (by 1–2 orders of magnitude) phosphorescence lifetimes in acetonitrile and dimethylformamide, contrary to their lifetimes in less polar chloroform and tetrahydrofuran, which are comparable to those for 3. The femtosecond transient absorption (fsTA) measurements confirmed the interconversion between the 3MLCT and 3ILCT excited-states in polar solvents. In contrast, the emissive state of 1 and 2 in less polar environments is of predominant 3MLCT nature.

Electrocatalytic reduction of CO2 to CO by a series of organometallic Re(i)-tpy complexes

“…The TA features of Re1–4 are similar to the earlier reports on the structurally analogous [Re(C 6 H 5 -tpy-κ 2 N)(CO) 3 Cl]. 74…”

“…The TA features of Re1-4 are similar to the earlier reports on the structurally analogous [Re(C 6 H 5 -tpyκ 2 N)(CO) 3 Cl]. 74 The various excited state processes are pictorially represented in a Jablonski diagram in Fig. 5.…”

“…65 The broad ESA in the mid-visible region (450 nm-600 nm) is assigned to the excitation of the MLCT state to higher states. 69 A broad excited state absorption band from 450 nm to 600 nm in [Re(R-tpy-κ 2 N)(CO) 3 Cl] has been assigned to the lowest triplet MLCT state. 67,68,70,71 The TA of Re5 has significantly different characteristics and warrants further investigation compared with the Re1 to Re4 complexes.…”

Structural and Photophysical Trends in Rhenium(I) Carbonyl Complexes with 2,2′:6′,2″-Terpyridines

“…The authors of [88] conducted comprehensive studies of photoinduced processes in 37 Cl and 40 Cl depending on the polarity of the environment, confirming the change in the nature of the triplet excited state from 3 MLCT to 3 ILCT in polar solvents. A bathochromic shift in the emission position of these systems in polar solvents was accompanied by the enhancement of the excited-state lifetime relative to the unsubstituted chromophore 1 Cl (Table S8).…”

“…The remote substituent impact in [ReX(CO) 3 (R-C 6 H 4 -terpy-κ 2 N)] was explored by the Fernández-Terán [63,64], Hanan [47], and Machura [46,59,60,78,82,87,88] research groups (Table S8). The authors of [63] conducted a comprehensive investigation of a series of complexes 1 Cl , 8 Cl , 31 Cl , 32 Cl , 34 Cl , 35 Cl , and provided definitive experimental evidence for a change in the excited-state character from 3 MLCT (1 Cl , 8 Cl , 31 Cl , 32 Cl and 34 Cl ) to 3 ILCT in [ReX(CO) 3 (R-C 6 H 5 -terpy-κ 2 N)] with the strongest electron-releasing substituent, -NMe 2 (35 Cl ).…”