As seen fromFig. 2, the dyes D1eD5 exhibit three distinct bands:
two relatively weak bands in the near-UV region (~305 nm and
~380 nm) corresponding to the p-p* electron transition, and
another strong absorption in the visible region (at approx. 500 nm)
that can be assigned to an ICT between the hydrazonetriphenylamine donating unit and the rhodanine-3-acetic acid
anchoring moiety. Small bathochromic shifts (8 nm and 10 nm) are
observed for dyes D2 and D3, bearing methyl or methoxy groups at
the p-phenyl positions of the triphenylamine fragment, with
respect to the spectra of the unsubstituted parent dye D1. The exchange of alkyl substituents, attached to the hydrazine moiety, has
very limited effect on thep-conjugation and ICT (if D4 and D5 are
compared with D2), indicating that the phenyl ring at the hydrazine
nitrogen is twisted with respect to the conjugation plane. Moreover, it can be concluded from the absorption curves of the reference D-p-A type dyeTPA-Rand D-D-p-A type dye D5 that the
attachment of the hydrazone moiety to the triphenylamine as
auxiliary donor shifts the absorption maxima in the visible region
by 16 nm and increases absorption intensity as well. The dyes
D1eD5 exhibit high extinction coefficients (Table 1), for example 3
of D2 (4.210
4M1cm
1
at 495 nm) is more than three times
higher than that of the standard Z907 ruthenium sensitizer
(3 ¼1.210
4M1cm
1
at 521 nm)[18]
C
NMR spectroscopy. Elemental analysis data was consistent with the
desirable structures.
3.2. Optical, electroch
As seen fromFig. 2, the dyes D1eD5 exhibit three distinct bands:two relatively weak bands in the near-UV region (~305 nm and~380 nm) corresponding to the p-p* electron transition, andanother strong absorption in the visible region (at approx. 500 nm)that can be assigned to an ICT between the hydrazonetriphenylamine donating unit and the rhodanine-3-acetic acidanchoring moiety. Small bathochromic shifts (8 nm and 10 nm) areobserved for dyes D2 and D3, bearing methyl or methoxy groups atthe p-phenyl positions of the triphenylamine fragment, withrespect to the spectra of the unsubstituted parent dye D1. The exchange of alkyl substituents, attached to the hydrazine moiety, hasvery limited effect on thep-conjugation and ICT (if D4 and D5 arecompared with D2), indicating that the phenyl ring at the hydrazinenitrogen is twisted with respect to the conjugation plane. Moreover, it can be concluded from the absorption curves of the reference D-p-A type dyeTPA-Rand D-D-p-A type dye D5 that theattachment of the hydrazone moiety to the triphenylamine asauxiliary donor shifts the absorption maxima in the visible regionby 16 nm and increases absorption intensity as well. The dyesD1eD5 exhibit high extinction coefficients (Table 1), for example 3of D2 (4.2104M1cm1at 495 nm) is more than three timeshigher than that of the standard Z907 ruthenium sensitizer(3 ¼1.2104M1cm1at 521 nm)[18]CNMR spectroscopy. Elemental analysis data was consistent with thedesirable structures.3.2. Optical, electroch
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