Detailed photophysical studies are presented for Cu<sub>2</sub>Cl<sub>2</sub>(dppb)<sub>2</sub> and Ag<sub>2</sub>Cl<sub>2</sub>(dppb)<sub>2</sub>. Both compounds show very effective thermally activated delayed fluorescence (TADF) at ambient temperature with an emission quantum yield of the Ag(I) complex of Φ<sub>PL</sub>(300 K) = 93 %. This emission is blue shifted by 65 nm (2500 cm<sup>-1</sup>) with respect to the emission of the Cu(I) complex, demonstrating a valuable strategy for engineering blue light emitters. Potentially, these materials are well suited for taking advantage of the singlet harvesting effect in an OLED device. Moreover, both compounds do not show effects of concentration quenching at high emitter concentration, a property which might be attractive for reducing the efficiency roll-off at higher current densities. Investigations down to T = 1.6 K show that spin-orbit coupling (SOC) is particularly weak. This is displayed in the very long emission decay times of the triplet states (T<sub>1</sub> states) of metal-toligand charge transfer (<sup>3</sup>MLCT) character, amounting to τ(Ag<sub>2</sub>Cl<sub>2</sub>(dppb)<sub>2</sub>) = 1.1 ms and τ(Cu<sub>2</sub>Cl<sub>2</sub>(dppb)<sub>2</sub>) = 2.2 ms. According to the TADF mechanism, which leads to the additional decay channel at ambient temperature via the S<sub>1</sub> state (of <sup>1</sup>MLCT character), an increase of the radiative rate by a factor of 70 and almost 500 for Ag<sub>2</sub>Cl<sub>2</sub>(dppb)<sub>2</sub> and Cu<sub>2</sub>Cl<sub>2</sub>(dppb)<sub>2</sub>, respectively, is induced. This results in radiative rates at ambient temperature of k<sub>r</sub> = 6.2 ∙ 10<sup>4</sup> s<sup>-1</sup> (τ<sub>r</sub> = 16 μs, Ag(I) complex) and 11.7 ∙ 10<sup>4</sup> s<sup>-1</sup> (τ<sub>r</sub> = 8.5 μs, Cu(I) complex). Simple approaches are presented that allow us to understand the weakness of SOC on the basis of results from DFT and TD-DFT calculations. Investigations of the emission decay properties down to T = 1.6 K further support the conclusions with respect to the SOC strength.
In an electroluminescent excitation, singlet and triplet excitons are generated. In this contribution it
is proposed to harvest all excitons in an efficiently emitting singlet state by use of molecules which
exhibit distinct thermally activated delayed fluorescence at T = 300K. Highly attractive examples,
comprising Cu(I) complexes and the metal-free acridine orange, are presented and discussed with
respect to their photophysical properties.
In this paper we report the spectral manifestation of existence two spectral forms of Pd-porphin in wide set of Shpol'skii
matrices at cryogenic temperatures. The short-wavelength spectral form is attributed to the structure, where the central
Pd(II) ion is in plane of the porphyrin macrocycle, while the long-wavelength form is associated with the nonplanar
saddle-type conformation of the PdP. The frequencies of the normal vibrations in the ground electronic state have been
measured separately for both forms and the differences in the normal modes of two macrocycle conformations are
discussed. The type of molecule distortion has been established with using information about the frequencies of vibronic
modes from high-resolved spectra of metalloporphins. Matrix effect was shown to have significant role in the stabilization of each of two conformations.