Optical spectra of oligothiophenes: vibronic states, torsional motions, and solvent shifts

Optical Bandgaps of π‐Conjugated Organic Materials at the Polymer Limit: Experiment and Theory

“…15). [12] The increase in the vertical transition energy E vert (abs) with temperature, caused by thermal excitation of low-frequency modes, is well reproduced by theory from a model based on undisplaced distorted oscillators ( Fig. 2) with the correct torsional frequencies in the S 0 and S 1 state used as input parameters and the vibrational lev- [9].…”

“…Solvent shifts can be as large as 0.3 eV for optically allowed transitions, even in nonpolar solvents where specific solute-solvent interactions are not expected. [9,12,79] For most of the molecules under consideration in the present review, gas-phase data are not available because of their low vapor pressure. A possible approach to experimentally evaluate solvent shifts relies on the Onsager model, which is based on a reaction-field model involving a spherical cavity.…”

“…The corresponding value in vacuum, with a standard deviation of ±0.02 eV, is obtained by linear extrapolation. It is also worth noting that temperature-induced spectral shifts are mainly a result of changes in the polarizability, induced by variations in the density of the solvent, [12] and only to a small extent a result of the planarization of the molecular backbone, which sum up to ca. 0.01-0.02 eV.…”

“…Experimental E vert (~) and E 00 (᭹, [12]) in vacuo, as obtained by Equation 10. HF RCIS/6-311+G* with geometry optimization of the S 1 state and C 2h symmetry restriction [12]. E 00 (᭺), E vert (~), obtained from Equations 2a and 6.…”

Observation of the β‐Phase in Two Short‐Chain Oligofluorenes

“…60 phenyl-rings; a value significantly longer than that reported for other conjugated polymers determined using similar procedures. Here, typical values range from 10 thiophene-rings in the polymer polythiophene [39] to 10-17 phenyl-rings in the polymer poly( p-phenylene vinylene). [40] Although significantly longer electronic conjugation lengths have been estimated from the conjugated polymer polydiactylene using interference techniques, [41] the device-applicable properties of polyfluorene polymers make the b-phase a truly remarkable molecularassembly.…”