Solvent effects on the UV/VIS absorption spectrum of bis-(dimethylamino)-heptamethinium chloride [(BDH)+Cl−]

Abstract The nature of the solvent has a small influence on the position of the longest wavelength absorption band and the oscillator strength (S 0 →S 1 transition) of (BDH) + Cl − . A linear correlation between the molar excitation energy of (BDH) + Cl − and the refractive index function f ( n ) = ( n 2 −1) / (2 n 2 +1) proves that dispersion forces are mainly responsible for the position of the longest absorption wavelength. Furthermore, the oscillator strength decreases with a rising value of the mentioned refractive index function. This means that dispersion forces cause a small disturbance of the ideal polymethine state in the first excited singlet state and lead to a decrease in the transition probability.