Geometry and torsional motion of biphenyl in the ground and first excited singlet state

Abstract

The lowest excited singlet state of biphenyl (BP) and a number of its isotopically and chemically substituted analogs have been studied by supersonic jet laser spectroscopy. The symmetry species of this excited state in BP can be classified as B 2-:; in the G I6 extended molecular symmetry group G I6 (EM). The symmetry-allowed origin of the biphenyl-h SI +-So electronic transition occurs at 35 268 cm-I. The frequency ofthe torsional moti~n in S is determined to be-65 cm-I. The potential parameters for this motion in SI are V 2 = 1195 1 cm-I, V 4 =-190 cm-I, and V6 = 18 cm-I. The torsional motion for the ground state (-50 cm-I) can be described by V 2 = 50 cm-1 and V 4 =-148 cm-I. The change in the dihedral angle between the two benzene rings in BP upon So to SI excitation is determined to be _44• based on a Franck-Condon factor calculation. Several fundamentals of the molecular vibrations are assigned in the SI state. The exciton interaction between the coupled benzene rings in biphenyl is suggested to be large (> 10 3 cm-1).

A Strategy for Controlling the Central Torsion Angle in Biphenyl‐Based Molecular‐Scale Bridges

“…[24] Relatively intense fluorescence is apparent in fluid solution and is centred around 340 nm ( Figure 2); the spectral profile and peak position are insensitive to changes in excitation wavelength. The excitation spectrum matches closely with the absorption profile for each polyether while the fluorescence and absorption bands show reasonable mirror [27] Fluorescence quantum yields (Φ F ) are about 0.10 and only slightly dependent on the length of the polyether strap (Table 1). Fluorescence decay profiles were strictly monoexponential regardless of monitoring wavelength and unaffected by the presence of dissolved molecular oxygen.…”

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

“…For B-type molecules (e.g., nPVs and long nTs (n ≥ 3)), the equilibrium geometry is planar in both the S 0 and S 1 states when T → 0 K, and yields a mirror symmetry. In C-type molecules (e.g., nPs) the equilibrium geometry is nonplanar in the ground state, [19][20][21] and there is no mirror symmetry between the absorption and emission, regardless of the temperature (Fig. 3c).…”

Chemically Controlled Conductivity: Torsion‐Angle Dependence in a Single‐Molecule Biphenyldithiol Junction

“…[15][16][17] Furthermore this type of unit has been considered as a potential conductance switch as the two p systems can be either in the same plane or perpendicular to each other representing the "on" and "off" states of a molecular switch, respectively. [18][19][20] In a recent study, Venkataraman [10] and co-workers reported the interdependence between the calculated molecular conformation and the single-molecule conductance of a series of various substituted biphenyls having terminal amino groups.…”