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Variable-temperature absorption and emission data over the range 80–300 K have been collected for 1,2-diphenylacetylene (DPA) and its derivatives, as well as 1,4-diphenylbuta-1,3-diyne (DPB) derivatives in 2-methyltetrahydrofuran (2-MeTHF). Moreover, the influence of temperature on fluorescence lifetime and quantum yield has also been investigated. A strong coupling between solvation dynamics and solute structure is observed in the low-temperature regime as well as at intermediate temperature where the structure of the compound is evolving in the course of excited-state relaxation. Moreover, the dependency of fluorescence quantum yield on temperature indicates that the energy of activation of radiationless transition for 1,2-diphenylacetylene and its derivatives is larger than the activation energy of viscous flow of 2-MeTHF, while for 1,4-diphenylbuta-1,3-diyne derivatives the opposite is observed. This finding implies that the conformational change of DPA and its derivatives in the excited state in 2-MeTHF shows an activation energy, contrary to DPB and its derivatives for which conformational changes are barrierless. [ABSTRACT FROM AUTHOR]

[Display omitted] • Thermochromic excited state dipole moment determination. • Discussion on state mixing in bicyclic chromophores under electric field influences. • Discussion of problems using thermochromic fluorescence spectroscopy. The excited state dipole moment of the lowest excited singlet state of 2,3-benzofuran in ethylacetate solution is determined using thermochromic spectroscopy and compared to the values which are obtained for the isolated molecule from electronic Stark spectroscopy (Hebestreit et al., 2020) and to the results of ab initio calculations at coupled cluster level of theory. It is shown that the dipole moment from thermochromic shifts in solution deviates considerably from that of the isolated molecule. This finding can be traced back to a field induced mixing by the strong reaction field of the solvent, which exceeds the external Stark field applied in gas phase measurements by a factor of 10.000. Depending on the dipole moments of the perturbing state and its energy gap to the excited state, dipole moments from thermochromic shifts (and consequently also of solvatochromic shifts) might be considerably different to gas phase values. However, the alteration of the electronic configuration of the molecule via the reaction field of the solvent can be deperturbed in the high-field limit. [ABSTRACT FROM AUTHOR]

• A theoretical DFT methodology may be used to tailor novel solar cell devices. • Lowest-energy structures at ground and excited states were computed in OPV materials. • Dihedral angles related to shifting of absorption maxima in UV–vis simulated spectra. • Descriptors obtained from electronic structure may aid to improve PV efficiencies. A density functional theory study was performed on a series of organic photovoltaic materials with a promising potential to be implemented as the active layer in a solar cell device. A thorough analysis on the molecular structure at ground and excited state revealed that some of the systems in the series of molecules observed in the ground state is dramatically altered in the first excitation. The dihedral deviations could be addressed as a ruling mechanism behind isomerization and its influence in the opto-electronic properties. The computation of absorption spectra at ground and excited state geometries showed a significant shift in the absorption maxima, presumably due to such geometrical changes. Furthermore, the computation of dipole moments gave us insights into the possible charge transfer from the OPV material to an acceptor in a solar cell device. This is critical when the system is implemented in such a device. Additionally, relevant photovoltaic parameters were collected, and a candidate series of OPV systems was proposed as potential materials for the heterojunctions of a solar cell device. The given theoretical methodology and the photovoltaic data computationally obtained may aid in the in silico design of novel donor materials for the new generation of solar cells. [ABSTRACT FROM AUTHOR]

• Dipole moment of 1-methylindole in its lowest excited singlet state has been determined from thermochromic shifts. • Discrepancies to ab initio values are explained by mixing of the excited states through the strong electric field of the solvent cavity. • The lower singlet state obtains dipole character from the upper state. • The difference to results from Stark spectroscopy are discussed. The permanent dipole moments of 1-methylindole in its ground and lowest excited singlet π π * -state have been determined using the method of thermochromic shifts of the absorption and fluorescence spectra and compared to ab initio calculated dipole moments. While ab initio theory predicts an excited state dipole moment, which nearly equals that of the ground state, the thermochromic shifts give an excited state dipole moment, which is about 2 Debye larger than that of the ground state. Perturbation of the excited state through the large electric field strength of the solvent cavity leads to strong mixing with the next excited singlet state, which has a considerably larger dipole moment. This perturbation is analyzed using the method described by Lombardi [John R. Lombardi J. Phys. Chem. A 1998, 102 , 2817–2823]. The perturbing state could be identified as 1 L a -state, which is the second adiabatic state in the gas phase, but the lowest state in a polar surrounding. [ABSTRACT FROM AUTHOR]