Excited-State Triplet Equilibria in a Series of Re(I)-Naphthalimide Bichromophores

Abstract

We present the synthesis, structural characterization, electronic structure calculations, and the ultrafast and supra-nanosecond photophysical properties of a series of five bichromophores of the general structural formula [Re(5-Rphen)(CO) 3 (dmap)](PF 6 ), where R is a naphthalimide (NI), phen = 1,10-phenanthroline, and dmap is 4-dimethylaminopyridine. The NI chromophores were systematically modified at their 4-positions with -H (NI), -Br (BrNI), phenoxy (PONI), thiobenzene (PSNI), and piperidine (PNI), rendering a series of metal−organic bichromophores (Re1−Re5, respectively) featuring variability in the singlet and triplet energies in the pendant NI subunit. Five closely related organic chromophores as well as [Re(phen)(CO) 3 (dmap)](PF 6 ) (Re6) were investigated in parallel to appropriately model the photophysical properties exhibited in the bichromophores. The excited state processes of all molecules in this study were elucidated using a combination of transient absorption spectroscopy and timeresolved photoluminescence (PL) spectroscopy, revealing the kinetics of the energy transfer processes occurring between the appended chromophores. The spectroscopic analysis was further supported by electronic structure calculations which identified the origin of many of the experimentally observed electronic transitions.

The switchable phosphorescence and delayed fluorescence of a new rhodamine-like dye through allenylidene formation in a cyclometallated platinum(ii) system

“…In addition, interesting delayed fluorescence at 620 nm of this rhodamine-like is also featured. Unlike the works from Castellano and co-workers about the transition metal systems with organic rylenes [62][63][64] which exhibited an equilibrium between the 3 MLCT and 3 IL states, the delayed fluorescence in this work is derived from an equilibrium between 1 IL and 3 IL states of Rhodyne. For the opened form of 2, higherenergy excitation for the 1 MLCT/LLCT transition of platinum(II) moiety or lower-energy excitation for the Rhodyne 1 IL state would also generate Rhodyne triplet intraligand ( 3 IL) excited state.…”

Visible-Light-Driven Triplet Sensitization of Polycyclic Aromatic Hydrocarbons Using Thionated Perinones

“…Additionally, the strong SOC that results from the heavy-atom effect also drastically shortens triplet lifetimes compared to those of many organic chromophores, , allowing nonradiative decay to outcompete TET. Many investigations have attempted to circumvent these issues by appending organic chromophores within the ligand framework, which strategically introduces a series of energy transfer cascades and triplet state thermal equilibria to achieve enhanced visible-light harvesting and extended triplet lifetimes. ,,− However, these bi- and polychromophoric transition metal architectures can be very cumbersome and tedious to design and synthesize, where it is also difficult to predict and control the achieved thermal equilibrium process and the resultant lifetime extension a priori . Among the previously mentioned obstacles, the significant cost and relatively low natural abundance of the second- and third-row transition metals typically used in these constructs limit the practicality of these systems for large-scale applications.…”

“…15,18,22−26 However, these bi-and polychromophoric transition metal architectures can be very cumbersome and tedious to design and synthesize, where it is also difficult to predict and control the achieved thermal equilibrium process and the resultant lifetime extension a priori. 23 Among the previously mentioned obstacles, the significant cost and relatively low natural abundance of the second-and third-row transition metals typically used in these constructs limit the practicality of these systems for large-scale applications. Thus, there is substantial interest in generating easily accessible organic triplet photosensitizers featuring strong visible absorbing cross sections, long excited state lifetimes, and redox properties amenable for photoredox catalysis.…”

Using Room Temperature Phosphorescence of Gold(I) Complexes for PAHs Sensing

“…The absorption spectra of the compounds display a vibronically structured band with spacings of 1368 cm −1 corresponding to π−π* intraligand transition of the naphthalimide ligand [ 9 , 22 , 24 , 38 , 39 , 40 , 41 ]. This band is ca.…”

“…455 nm due to the intraligand fluorescence emission of the naphthalimide group and another at longer wavelengths (ca. 620 nm) attributed to the phosphorescence of the chromophore [ 12 , 22 , 23 , 39 , 41 ]. The phosphorescence assignment is evidenced by the quenching of the intensity of this emission band in the presence of oxygen ( Figure S10 ) and can be achieved thanks to the presence of the gold(I) heavy atom that favors the intersystem crossing and population of the emissive triplet state [ 42 ].…”