Synthesis and electronic properties of 1,2-hemisquarimines and their encapsulation in a cucurbit[7]uril host.
The synthesis of a new class of robust squaraine dyes, colloquially named 1,2-hemisquarimines (1,2-HSQiMs), through the microwave-assisted condensation of aniline derivatives with the 1,2-squaraine core is reported. In CH3CN, 1,2-HSQiMs show a broad absorption band with a high extinction coefficient and a maximum at around λ=530 nm, as well as an emission band centered at about λ=574 nm, that are pH dependent. Protonation of the imine nitrogen causes a redshift of both absorption and emission maxima, with a concomitant increase in the lifetime of the emitting excited state. Encapsulation of the chromophore into a cucurbit[7]uril host revealed fluorescence enhancement and increased photostability in water. The redox characteristics of 1,2-HSQiMs indicate that charge injection into TiO2 is possible; this opens up promising perspectives for their use as photosensitizers for solar energy conversion.
Department of Chemical Sciences, University of Padova, Via Marzolo 1, 35131 Padova (Italy), Fax: (+) 30 0498275050.
Christian C
CC
De Filippo
Hao
H
Tang
Luca
L
Ravotto
Giacomo
G
Bergamini
Patrizio
P
Salice
Miriam
M
Mba
Paola
P
Ceroni
Elena
E
Galoppini
Michele
M
Maggini
cucurbiturils; dyes/pigments; host-guest systems; photochemistry; sensitizers; squaraines