Essential state models for solvatochromism in donor-acceptor molecules: the role of the bridge.
Essential state models are presented to discuss absorption spectra of two related donor-acceptor (DA) chromophores that show two solvatochromic bands in the near-infrared spectral region. The two-state model only accounts for the lowest energy band and results in a very small value of mu(0), the dipole moment associated with the D(+)A(-) state. The model is then extended to account for the active role of the bridge: the resulting three-state model satisfactorily reproduces the double solvatochromism, leading at the same time to a roughly doubled estimate of mu(0). This result, supported by a detailed analysis of an N-state model that explicitly accounts for bridge states, rationalizes the well-known discrepancy between the geometrical DA distance and the dipole length extracted from the analysis of optical spectra of DA chromophores as reflecting the active role of bridge states, not explicitly accounted for in essential state models.
Grisanti
Luca
L
Dipartimento Chimica GIAF, Parma University, and INSTM-UdR Parma, I-43100 Parma, Italy.
D'Avino
Gabriele
G
Painelli
Anna
A
Guasch
Judith
J
Ratera
Imma
I
Veciana
Jaume
J