Solvent effects on the photophysical properties of Bu4N[(4,4′-bpy)Re(CO)3(bpy-5,5′-diCOO)] complex. A combined experimental and computational study

Abstract

The photophysical properties of the complex Bu 4 N[(4,4′-bpy)Re(CO) 3 (bpy-5,5′-diCOO)] were studied in protic and aprotic media with the aid of steady-state and time-resolved techniques and TD-DFT calculations. The absorption spectrum as well as the steady state and time resolved luminescence of the Re(I) complex display a marked solvent effect. The highest and lowest energy absorption bands experience a bathochromic shift as the polarity of the solvent decreases. In addition, the lowest energy band broadens. Two luminescence bands were observed around 430 and 600 nm in protic organic solvents like alcohols. The high energy emission is observed solely in aqueous solutions, while in aprotic solvents only the low energy luminescence is detected. TD-DFT calculations allowed us to identify the main electronic transitions in the low energy region as 1 MLLCT Re(CO) 3 → 4,4′-bpy and 1 MLLCT Re(CO) 3 → bpy-5,5′-diCOO . The simulated absorption spectra of the Re(I) complex in H 2 O, protic (EtOH, MeOH) and aprotic (CHCl 3 , CH 2 Cl 2 , CH 3 CN) organic solvents follow the experimental absorption spectra with reasonable accuracy both in position and relative intensities. The magnitude of the calculated dipole moment (μ) increases with the dielectric constant of the solvent (ε r ). Besides, the energy of 1 MLLCT Re(CO) 3 → 4,4′-bpy also increases with ε r . However, the energy of the 1 MLLCT Re(CO) 3 → bpy-5,5′-diCOO transition is rather insensitive to ε r . This disparity is attributed to the fact that the 1 MLLCT Re(CO) 3 → 4,4′-bpy transition is nearly parallel to the orientation of μ while the 1 MLLCT Re(CO) 3 → bpy-5,5′-diCOO transition is almost perpendicular to it. Unrestricted TDFT calculations were successfully applied to the triplet species. It is observed that in the triplet state the Re N distances are shortened while Re C distances are elongated relative to the ground state. The calculated emission energy by TD-DFT and/or Δ(SCF) methods was compared to the experimental emission maximum in chloroform. All the experimental results as well as the theoretical calculations indicate that solvent effects on the steady state and time resolved luminescence of the Re(I) complex can be accounted by the coexistence of 3 MLLCT Re(CO) 3 → 4,4′-bpy , 3 MLLCT Re(CO) 3 → bpy-5,5′-diCOO and 1 IL excited states.

Rhenium(I) Complexes with Neutral Monodentate Coligands and Monoanionic 2-(1,2,4-Triazol-5-yl)pyridine-Based Chelators as Bidentate Luminophores with Tunable Color and Photosensitized Generation of 1O2: An Integrated Case Study Involving Photophysics and Theory

“…In general, the biexponential lifetimes can be explained by taking into account different effects, as has been previously seen for a vast number of rhenium­(I) tricarbonyl complexes. ,,,− On the one hand, in fluid solutions, different conformations can be thermally accessed with comparable excited-state character yet different deactivation rates, as observed for A-Br , F-Br , and F-CN . Moreover, diverse emitting states could coexist in thermal equilibrium, which might be influenced by the microenvironment affecting the excited states’ character.…”

Photophysics and photochemistry of carminic acid and related natural pigments

“…Aqueous solutions of the samples and a calorimetric reference (CR, New Coccine, a R = 1) were matched within 2% of absorbance values between 0.1 and 0.2 at the laser wavelength. 24 Experiments were performed under a controlled atmosphere, obtained by purging the solutions with N 2 or O 2 , for 15 min.…”