The site-to-site intramolecular excitation transfer and excitation trapping on one site in amino-substituted triphenylbenzene derivatives, which are characterized by a 3-fold symmetry, have been studied by fluorescence spectroscopy and time-resolved microwave conductivity (TRMC). The importance of dipole relaxation due to intramolecular energy transfer has been demonstrated in the interpretation of the limiting anisotropy on one hand and the change of the dipole moment and polarizability upon excitation on the other hand. The interpretation of the experimental results is based on the comparison of the molecules with C3-symmetry with biphenyl model compounds.

This paper is devoted to two new aromatic polyamines derived from p-EFTP (5‘-(4-(bis(4-ethylphenyl)amino)phenyl)-N,N,N‘,N‘-tetrakis(4-ethylphenyl)-1,1‘:3‘,1‘‘-terphenyl-4,4‘‘-diamine) and exhibiting meta connections around a central phenylene ring. In p-EFDP (5‘-phenyl-(N,N,N‘,N‘-tetrakis(4-ethylphenyl)-1,1‘:3‘,1‘‘-terphenyl-4,4‘‘-diamine) there are only two redox sites instead of three. Upon partial oxidation, an intervalence transition is observed from which an electronic coupling very similar to the one of p-EFTP is obtained. In p-FADP (N,N,N‘,N‘,N‘‘,N‘‘-hexakis(4-ethylphenyl)-1,1‘:3‘,1‘‘-terphenyl-4,4‘‘,5‘ triamine) one finds two redox sites of the N,N‘-bis(4-ethylphenyl)-4-aminobiphenyl type, and one redox site of the triphenylamine type. The analysis of the electrochemical behavior and of the intervalence transitions in the mono- and dioxidized species allows the distinction among the different types of electron transfer.

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The photophysical properties of a diphenyl amino-substituted triphenylbenzene, (pEFTP), biphenyl (pEFBP), and fluorene (pEFF) derivative are compared. The similarity of the photophysical properties and their solvent dependence for the triphenylbenzene and the biphenyl model compound indicate the formation of a polar excited state, localized in one branch of pEFTP. Further comparison with the fluorene model compound suggests an excited state relaxation process of the biphenyl moiety in solvents of medium and high polarity toward a more planar geometry. The depopulation of the excited state is explained in the framework of the model developed to rationalize the photophysics of substituted biphenyl.