Influence of Disorder on Electronic Excited States:  An Experimental and Numerical Study of Alkylthiotriphenylene Columnar Phases

Abstract

The spectroscopic properties of discotic hexa-alkylthiotriphenylenes are studied in solution and thin films and compared to those of hexa-alkyloxytriphenylenes. The solution properties are analyzed in the light of CS-INDO-CIPSI quantum chemistry calculations. The absorption maximum is assigned to the degenerate S 0 f S 4 transition. The fluorescence of the neat phases is attributed to weakly bound excimers. The phase transition leading from ordered to disordered columnar stacks induces an increase in the oscillator strength of the S 0 f S 1 transition and favors excimer formation. The influence of structural disorder on the properties of the delocalized states is rationalized by using various approximations within the frame of the exciton theory; three models for the calculation of the exciton coupling (point dipole, extended dipole, atomic transition charge distribution) are tested, short and long range interactions are considered, and the introduction of a dielectric constant is discussed. The best agreement between experimental and calculated absorption maxima is obtained using the atomic charge transition model. Off-diagonal disorder is correlated to structural disorder by changing the orientation and the position of the molecules within the aggregate. The case of degenerate molecular states is compared to that of nondegenerate ones. Orientational disorder has a dramatic effect on the energy and the localization of the upper eigenstate when molecular states are nondegenerate. Conversely, the properties of degenerate eigenstates are quite insensitive to orientational disorder. The magnitude of the off-diagonal disorder induced by positional disorder largely depends on the model used in the calculation of the exciton coupling. The results of the numerical calculations are in agreement with the small change observed in the neat phases absorption maxima upon a quasi one-dimensional melting of columnar stacks.

Isocyano-Triphenylene Complexes of Gold, Copper, Silver, and Platinum. Coordination Features and Mesomorphic Behavior

“…As for the electronic spectra, all the emission spectra are similar, with the maximum in the range 421-467 nm (Figure 2), typical of fluorescent 2,3,6,7,10,11-hexaalkoxytriphenylenes. 43,44 The quantum yields for the metal complexes, Φ, measured in dichloromethane solution at room temperature, 46 are considerably lower than for the free isocyanide ligand (Figure 2). It is probable that the presence of the metallic fragment (heavy atom effect) enhances non-radiative deactivation processes.…”

“…In the solid state, the luminescence of these derivatives is lost, as reported for hexaalkoxytriphenylenes. 43,44 Figure 2. Excitation and emission spectra of the free isocyanide and the complex [Au(C 6 F 5 )(CN-TriPh)] (2).…”

Exciton delocalization, charge transfer, and electronic coupling for singlet excitation energy transfer between stacked nucleobases in DNA: An MS-CASPT2 study

“…Here one of the most common approaches is the calculation of the Coulomb couplings using the transition density, 10 in particular using the atomic transition charge density (in short, the transition charges). 11 The second approach is based on a transformation of the eigenstates of the Hamiltonian to a diabatic basis. In this case one obtains directly the whole couplings and not their components.…”

UV Spectra and Excitation Delocalization in DNA: Influence of the Spectral Width

“…New methodologies, introducing quantum chemistry methods in the calculation of the diagonal and off-diagonal terms, were applied in the investigation of various systems such as molecular aggregates and photosynthetic antennas (see for example refs. [13][14][15][16][17][18]). Thus, subtle differences appeared in the properties of various systems and the effect of structural disorder could be evaluated.…”