Abstract
A significant bathochromic shift of the fluorescent and long-wavelength absorption bands of [2.2] paracyclophane comparing to corresponding bands of alkyl-benzenes is due to a strong transannular interaction, resulting in formation of a principally new excited state of lower energy. It is concluded that the fluorescent levels for alkylbenzene excimers and for the macrocycle are of the same nature. Analysis of [2.2] paracyclophane mono- and diphenylderivatives spectra shows that their intensive absorption bands (230–310 nm) are originated from electron transitions of biphenyl groups and weak long wavelength absorption (310–340 nm) and fluorescent bands are governed by the same electron transitions between ground and excimer-like excited states as in the case of non-substituted macrocycle.
Highlights
It is well known, that UV-irradiation of organic luminophores solutions initiates in these systems photophysical and photochemical processes, which are essentially depended on interactions between molecules in excited and nonexcited states
It is estimated that the main reason of significant bathochtomic shift of [2.2] paracyclophane ([2.2] PCP) fluorescent and long-wavelength absorption bands compared with the corresponding bands for molecules containing non-conjugated benzene chromophores is a strong transannular interaction between π-orbitals of closely spaced benzene rings of the macrocycle
The [2.2] PCP fluorescence band location at longer wavelength compared with polystyrene excimer emission band is explained by the fact that macrocycle HOMO energy level is situated higher than that of alkyl-substituted benzenes [1]
Summary
That UV-irradiation of organic luminophores solutions (included solid solutions in polymer) initiates in these systems photophysical and photochemical processes, which are essentially depended on interactions between molecules in excited and nonexcited states. It is estimated that the main reason of significant bathochtomic shift of [2.2] paracyclophane ([2.2] PCP) fluorescent and long-wavelength absorption bands compared with the corresponding bands for molecules containing non-conjugated benzene chromophores is a strong transannular interaction between π-orbitals of closely spaced benzene rings of the macrocycle.
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