The relaxation dynamics of the indoline dye D149, a well-known sensitizer for photoelectrochemical solar cells, have been extensively characterized in various organic solvents by combining results from ultrafast pump-supercontinuum probe (PSCP) spectroscopy, transient UV-pump VIS-probe spectroscopy, time-correlated single-photon counting (TCSPC) measurements as well as steady-state absorption and fluorescence. In the steady-state spectra, the position of the absorption maximum shows only a weak solvent dependence, whereas the fluorescence Stokes shift Dñ F correlates with solvent polarity. Photoexcitation at around 480 nm provides access to the S 1 state of D149 which exhibits solvation dynamics on characteristic timescales, as monitored by a red-shift of the stimulated emission and spectral development of the excited-state absorption in the transient PSCP spectra. In all cases, the spectral dynamics can be modeled by a global kinetic analysis using a time-dependent S 1 spectrum. The lifetime t 1 of the S 1 state roughly correlates with polarity [acetonitrile (280 ps) o acetone (540 ps) o THF (720 ps) o chloroform (800 ps)], yet in alcohols it is much shorter [methanol (99 ps) o ethanol (178 ps) o acetonitrile (280 ps)], suggesting an appreciable influence of hydrogen bonding on the dynamics. A minor component with a characteristic time constant in the range 19-30 ps, readily observed in the PSCP spectra of D149 in acetonitrile and THF, is likely due to removal of vibrational excess energy from the S 1 state by collisions with solvent molecules. Additional weak fluorescence in the range 390-500 nm is observed upon excitation in the S 0 -S 2 band, which contains short-lived S 2 -S 0 emission of D149. Transient absorption signals after excitation at 377.5 nm yield an additional time constant in the subpicosecond range, representing the lifetime of the S 2 state. S 2 excitation also produces photoproducts.

Molecular emitters that combine circularly polarized luminescence (CPL) and high radiative rate constants of the triplet exciton decay are highly attractive for electroluminescent devices (OLEDs) or next-generation photonic applications, such as spintronics, quantum computing, cryptography, or sensors. However, the design of such emitters is a major challenge because the criteria for enhancing these two properties are mutually exclusive. In this contribution, we show that enantiomerically pure {Cu­(CbzR)­[( S/R )-BINAP]} [R = H (1), 3,6-tBu (2)] are efficient thermally activated delayed fluorescence (TADF) emitters with high radiative rate constants of k TADF up to 3.1 × 105 s–1 from 1/3LLCT states according to our temperature-dependent time-resolved luminescence studies. The efficiency of the TADF process and emission wavelengths are highly sensitive to environmental hydrogen bonding of the ligands, which can be disrupted by grinding of the crystalline materials. The origin of this pronounced mechano-stimulus photophysical behavior is a thermal equilibrium between the 1/3LLCT states and a 3LC state of the BINAP ligand, which depends on the relative energetic order of the excited states and is prone to inter-ligand C–H···π interactions. The copper­(I) complexes are also efficient CPL emitters displaying exceptional dissymmetry values g lum of up to ±0.6 × 10–2 in THF solution and ±2.1 × 10–2 in the solid state. Importantly for application in electroluminescence devices, the C–H···π interactions can also be disrupted by employing sterically bulky matrices. Accordingly, we have investigated various matrix materials for successful implementation of the chiral copper­(I) TADF emitters in proof-of-concept CP-OLEDs.

In this work we revisit and re-evaluate the photophysical behavior of the prototypical complex [Zn(SC 6 H 4 -4-R) 2 (phen)] as the most in-depth studied type of Zn(II)-based triplet state emitters. Previous reports suggest population of ligand-toligand charge transfer (LLCT) states via phenanthroline localized ππ* states, with an energy barrier between the 3 ππ* and the bk; 1/3 LLCT states requiring thermal activation. Besides very weak prompt fluorescence, the dominant radiative mechanism was attributed to phosphorescence. Our photophysical studies, including temperature-dependent quantum yield determination and time-resolved luminescence measurements, reveal a high radiative rate constant k r = 3.5 × 10 5 s À 1 at room temperature and suggest thermally activated luminescence as the major emission path. High-level DFT/MRCI calculations confirm this assignment and provide deeper insight into the excited-state kinetics, including rate constants for the (reverse) intersystem crossing processes. Thus, our study demonstrates that further optimization of the photophysical properties of this type of Zn(II) triplet exciton emitter bears great potential for future application in devices.

Molecular emitters that combine circularly polarized luminescence (CPL) and high radiative rate constants of the triplet exci-ton decay are highly attractive for electroluminescent devices (OLEDs) or next generation photonic applications, such as spintronics, quantum computing, cryptography or sensors. However, the design of such emitters is a major challenge because the criteria for enhancing these two properties are mutually exclusive. In this contribution, we show that enantiomerically pure [Cu(CbzR)((S/R)-BINAP)] (R = H (1), 3,6-tBu (2)) are efficient TADF emitters with high radiative rate constants of kTADF up to 3.1·105 s-1, and exceptional dissymmetry values of the emission glum of ±0.7·10-2 in THF solution and ±2.3·10-2 in the solid state are observed. Importantly for application in electroluminescence devices, the efficiency of the TADF pro-cess and emission wavelengths are highly sensitive to environmental hydrogen bonding of the ligands, which can be disrupt-ed either by grinding of the crystalline materials or by employing sterically bulky matrices. Accordingly, we have investigat-ed various matrix materials for successful implementation of the chiral copper(I) TADF emitters in proof-of-concept CP-OLEDs.