Photophysics of two Prototypical Molecular‐Wire Building Blocks: Solvent‐Induced Conformational Dynamics?

Abstract

The photophysics of two molecular wire building blocks of different lengths based on p-phenyleneethylene, namely, 1,4-bis[p-(N,N-dimethylamino)phenyl]-1,2-ethyne and 1,4-bis[p-(N,N-dihexylamino)phenylethynyl]benzene, are studied experimentally in a wide range of organic solvents. The band shape and position of the electronic absorption and fluorescence emission of both compounds are discussed in terms of the empirical Catalán linear solvent energy relationship and the analytical solvation model of Liptay. It is found that solute polarizability plays an important part in the description of the pronounced solvatochromism for these highly symmetric molecules. In addition, the dependence of the emission quantum yield and the excited-state lifetime on the solvent are measured. The experimental findings can only be partially rationalized by the common theoretical models. They indicate that not only torsion about the triple bonds but also solvent-solute reorganization must be taken into account.

Oligo(p‐phenyleneethynylene) (OPE) Molecular Wires: Synthesis and Length Dependence of Photoinduced Charge Transfer in OPEs with Triarylamine and Diaryloxadiazole End Groups

“…Previously a symmetric DBD amine-OPE-amine system like 6, namely 1,4-[(C 6 H 13 ) 2 NC 6 H 4 CC] 2 C 6 H 4 was reported to possess significant solvatochromism despite having an excited state with assumed overall zero dipole moment. [32] For 7 on the other hand, there is very little impact on the fluorescence with different medium polarity ( Figure S6) both with respect to spectral progression and QY. This supports the notion that the significantly red-shifted emission in polar media for the shorter compounds 1-3 with Stokes shifts of 6970-8680 cm -1 can be ascribed to ICT states.…”

Solvatochromic studies of pull–push molecules containing dimethylaniline and aromatic hydrocarbon linked by an acetylene unit

“…In non-polar solvents, substantial asymmetry between absorption and emission spectra is observed. Such phenomenon occurs not only for the arylethynyl derivatives of N,Ndimethylaniline (DMA), 8,39 but also for phenylene ethynylene oligomers [40][41][42][43][44] and have been explained in terms of torsional disorder and quadratic coupling between the ground and the rst excited state 45 or the exciton model developed by Liu et al 46,47 The increase of solvent polarity causes bathochromic shi of emission spectra and disappearance of their vibronic structure. For both naphthalene derivatives spectra shi from about 27 400 cm À1 for iso-octane to 20 000 cm À1 in DMSO, whereas for AacDMA from 22 200 cm À1 to 16 300 cm À1 .…”

Experimental and theoretical studies of the spectroscopic properties of simple symmetrically substituted diphenylacetylene derivatives

“…[12][13][14][15][16][17][18][19] Likewise, rather rigid, highly conjugated poly(p-phenylenethynylene)s are strongly uorescing. [20][21][22][23][24][25][26][27][28][29][30] 1,2-Diphenylethyne (tolane, DPA) and diphenylbuta-1,3-diyne behave quite differently. The photophysics of the two simplest aryl derivatives of acetylene and diacetylene were studied both experimentally 28,[31][32][33][34][35][36][37][38][39][40][41][42] and theoretically.…”