Theoretical study of generalized oscillator strengths for the low-lying electronic excitations of CH3Cl and CF3Cl

We report a theoretical study of electronic excitation in CH3Cl and CF3Cl by electron impact. Momentum-transfer-dependent generalized oscillator strengths (GOSs) are calculated for transitions to low-lying excited singlet-states at the equation-of-motion coupled-cluster singles and doubles level. The influence of molecular vibration is taken into account in the calculation. The theoretical results show reasonable overall agreement with experimental data reported in the literature. The shapes of the GOS profiles reveal that the 1 1E state of CH3Cl has a valence-Rydberg mixed nature, while that of CF3Cl is of a predominant C-Cl antibonding character. A comparison with the experimental GOSs of CH3Cl provides unambiguous evidence that the 3pe state is lower in energy than the 3pa1 state. Optical oscillator strengths are also calculated and comparison is made with available experimental and other theoretical results.

Structure and photophysics of rubrene-tetracene blends

The application potential of singlet fission (SF), describing the spontaneous conversion of an excited singlet into two triplets, underlines the necessity to independently control SF rates, energetics and the optical band gap. Heterofission, whereby the singlet splits into triplets on chemically distinct chromophores, is a promising approach to control the above-mentioned parameters, but its details are not yet fully understood. Here, we investigate the photophysics of blends of two prototypical SF chromophores, tetracene (TET) and rubrene (RUB) using time-resolved photoluminescence spectroscopy and time-correlated single photon counting (TCSPC) to explore the potential for heterofission in combinations of endothermic SF chromophores.

Searching Building Blocks with Large Excited-State Gaps in Five-memebered Heterocyclic Rings by Aromaticity Strategy

Organic molecules with large gap between the excited singlet/triplet states can be applied in hot exciton emission and singlet fission to beat the spin statistics limit in optoelectronic devices. Herein, a novel strategy is proposed for achieving large triplet-triplet gap (E(T1T2)) and singlet-triplet gap (E(S1T1)) by manipulating the aromaticity of the low-lying excited states. Partially conjugated five-membered heterocyclic rings are found to naturally have low E(T1) owing to high aromaticity obeying Baird’s Rule. Utilizing such ring (pyrazoline) as a bridge and selecting various donor and acceptor moieties, numbers of derivatives have been theoretically designed with tunable emission colors, significantly large E(T1T2) and E(S1T1), and satisfying E(T2)>E(S1)≥2E(T1). The ultrafast spectroscopy and sensitization measurements for one of them with blue fluorescence (named TPA-DBPrz) confirm the calculated prediction. This work opens a new avenue and provides molecular units to develop high-efficiency optoelectronic materials.

Hydrogen atom transfer in the photochemical isomerization of hydrazones of 1,2,4-oxadiazole derivatives

DFT calculations on the photoisomerization of hydrazones of 1,2,4-oxadiazole derivatives to 1,2,5-triazoles have been performed showing that the reaction occurred through the first excited singlet state. The Z isomer gave the reaction through a hydrogen atom transfer of the hydrazonic nitrogen atom to the nitrogen atom in four position on the oxadiazole ring. In this case, the isomerization was a concerted reaction. The E isomer could undergo the same reaction. However, it could not be a concerted reaction but required the presence of a ring opening intermediate.

Wavelength dependent photochemistry of BODIPY–phenols and their applications in the fluorescent labeling of proteins

The molecules undergo wavelength dependent photochemistry, since photodeamination to QMs takes place only upon excitation to higher excited singlet states, showing unusual anti-Kasha photochemical reactivity.