Models CS INDO

CONSTRUCTION OF MOLECULAR WAVEFUNCTIONS AND POTENTIAL SURFACES THE CS INDO MODEL... 

In summary, all the experiments expressly selected to check the theoretical description provided fairly clear evidence in favour of both the basic electronic model proposed for the BMPC photoisomerization (involving a TICT-like state) and the essential characteristics of the intramolecular S and S, potential surfaces as derived from CS INDO Cl calculations. Now, combining the results of the present investigation with those of previous studies [24,25] we are in a position to fix the following points about the mechanism and dynamics of BMPC excited-state relaxation l)photoexcitation (So-Si)of the stable (trans) form results in the formation of the 3-4 cis planar isomer, as well as recovery of the trans one, through a perpendicular CT-like S] minimum of intramolecular origin, 2) a small intramolecular barrier (1.-1.2 kcal mol ) is interposed between the secondary trans and the absolute perp minima, 3) the thermal back 3-4 cis trans isomerization requires travelling over a substantial intramolecular barrier (=18 kcal moM) at the perp conformation, 4) solvent polarity effects come into play primarily around the perp conformation, due to localization of the... 

A CS INDO scheme incorporating solvent polarity effects according to Klopman s model is applied to examine geometric modification and solvatochromism of merocyanine dyes exhibiting peculiar behaviours. Qualitatively speaking, the model reproduces quite well the most important effects. The advantages of the CS INDO-solvaton approach with respect to other semiempirical procedures including solvation are discussed. 

Lastly, we want to point out that the CS INDO based procedure reported here is capable of correctly describing solvent effects on both ground- and excited-state properties by one and the same hamiltonian. This represents a methodological improvement with respect to all other semiempirical approaches that are forced to use different model hamiltonians (e.g. INDO, INDO/S) for geometry optimization and electronic structure calculation, or to bypass the problem of a direct geometry optimization resorting to empirical relationships between bond lengths and bond indexes. 

---