Optical properties trimers

Trimerized organic conductors are of special interest, because two electrons per three sites constitute the simplest situation, where both electronic transitions resulting in single- and double-site occupation take place [21]. As one considers larger n-mers, two complications arise. First, the number of equations that should be solved sharply increases. The second complication is the increase in the number of n-meric normal modes, which are coupled to an external electromagnetic field. Recently, Yartsev et al. [22] have proposed using the linear response theory for several variables to describe the optical properties of trimers with arbitrary equilibrium charge density distribution. This approach can be extended to any cluster—the size is limited only by computer facilities. 

Recently, the trimer theory has been used for the interpretation of the optical properties of the. Ymethylthiouronium salt [(MT)2(TCNQ)3 2H2Oj [67,68], The dominant feature of the polarized reflection spectrum cf (MT)2(TCNQ)3 2H20 (Fig. 13) is a broad intensive band of electronic reflection, with a sharp edge and low minimum at the frequency co = 9090 cm The intensive structure observed in the middle IR range (lines lto 8) is attributed to the e-mv coupling. Lines 2 and 4 have a fine structure which could be understood if one takes into account the equilibrium charge density shift pb = 0.25e and 3g = 0.15< in the two halves of TCNQ ( 3). 

Nagata, T., Osuka, A., Maruyama, K. (1990). Synthesis and optical properties of confor-mationally constrained trimeric and pentameric porphyrin Arrays, J. Am. Chem. Soc., Ill 3054. 

The question of the applicability of the semiclassic adiabatic approach to the vibronic problems in the JT systems is rather complicated in general and the thorough answer can be done with regard to a particular problem. In our brief discussion of this question we will refer to two areas - thermodynamic properties and resonance (optical) problems. In Ref. [9] the magnetic properties of mixed-valence dimeric and trimeric clusters are considered in the framework of... 

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