Molecular system stable state

One solution to the problem of semiconductor photodecomposition is to modify the spectral response of a stable wide-band-gap semiconductor so that solar energy can be efficiently utilized. This can be accomplished by adding to the electrolyte a dye that has absorption features that overlap the solar spectrum. The short excited-state lifetimes of molecular systems limit the distance an excited state can be expected to diffuse prior to nonradiative deactivation. Thus,... 

Switching also implies molecular and supramolecular bistability since it resides in the reversible interconversion of a molecular species or supramolecular system between two thermally stable states by sweeping a given external stimulus or field. Bistability in isolated molecules or supermolecules is, for instance, found in optical systems such as photochromic [8.229] or thermochromic substances or devices, in electron transfer or magnetic processes [8.239], in the internal transfer of a bound substrate between the two binding sites of a ditopic receptor (see Section 4.1 see also Fig. 33) [6.77]. Bistability of polymolecular systems is of a supramolecular nature as in a phase transition or a spin transition, both of which involve an assembly of interacting species. 

In principle any molecule able to exist in two reversible, switchable states can represents a molecular switch (bistable device) with potential to form part of molecular circuitry or act as molecular memory. An excellent component for switchable molecular devices is the 1,2-dithienylethene system, which has been exploited ingeniously by Lehn in a number of bistable systems.54 The core switching element is the transformation of the dithienylethene unit between two stable states as a function of the wavelength of incident radiation (Scheme 11.8). 

A few chapters of the current volume describe different state-of-the-art experimental techniques used to unravel photophysical and photochemical properties of complex molecular systems. These chapters are especially tailored for the scholarly description of electronic excited state properties of nucleic acid bases and related species predicting different tautomeric distributions and possible nonra-diative deactivation processes. It is interesting to note that guanine provides particularly challenging case to discuss. Recent theoretical and experimental investigations show the existence of relatively significantly less stable imino tautomers in the... 

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