Nonlinear absorption in a series of Donor–π–Acceptor cyanines with different conjugation lengths

Abstract

A detailed experimental and theoretical study of the linear and nonlinear absorption of a series of asymmetrical D-p-A cyanine dyes with the same trimethylindolin donor (D) and diethylaminocoumarin-dioxaborine acceptor (A) terminal groups and different conjugation lengths, is presented. Strong solvatochromic behavior affecting the fluorescence quantum yields, lifetimes, and the linear and nonlinear absorption properties is observed due to the presence of permanent ground state dipole moments. Detailed experimental studies of lifetime dynamics are performed by direct time-correlated single photon counting and pump-probe techniques. We find that an increase in p-conjugation in the investigated series of dyes leads to an enhancement of the excited-state absorption and two-photon absorption (2PA) cross-sections (d 2PA ). The 2PA spectra for all of the investigated dyes consist of two well-separated bands. The first band occurs at two-photon excitation into the vibrational levels and not into the absorption peak of the main transition, S 0 / S 1 , which is more typical of that observed for symmetrical cyanines. The position of the second 2PA band for all the molecules remains unchanged in solvents of different polarity contrary to the large solvatochromic shift of the S 0 / S 1 band, resulting in a large intermediate state resonance enhancement and, therefore, a larger 2PA in acetronitrile (d 2PA z 10000 GM) compared to toluene (d 2PA z 4700 GM). Experimental methods and results Materials characterization and linear spectroscopic propertiesThe molecular structures of the dyes studied in this paper are shown in the inset of Fig. 1a-c. Their chemical names are:

Molecular design of near infrared polymethine dyes: A review

“…As an illustration, the absorption spectra of dyes 4 derivatives of aminocoumarine synthesized by A.O. Gerasev et al [83][84][85][86][87] are presented in Figure 1b.…”

“…Gerasev et al [155][156][157] for the anionic polymethine dyes 4. Combined quantum-chemical and spectral studies of the dyes 4 [85][86][87] have shown that two lowest electron transitions are split transitions, involving two low positioned acceptor levels, in contrast to the cationic cyanine dyes where two lowest transitions are connected with two split donor levels.…”

Localized Emitting State and Energy Transfer Properties of Quadrupolar Chromophores and (Multi)Branched Derivatives

“…As a result, the excitation is efficiently localized, together with degeneracy of the two orthogonally polarized degenerate excited states strongly removed because of structure disorder and solvation, 26 leading to the decreased anisotropy value in the high-energy ICT side as shown in Figure 3. 13,66 Regarding chromophore 5, conjugation among the triphenylamine core and three branches through CC do exist, but it is not as strong as that in chromophore 4 because of the small twisting barrier of the CC bond. 10,58 Therefore, in chromophore 5, for low-energy ICT states, triphenylamine core is more active, charge is partially distributed overall molecule, and the CDD distribution at each branch agrees with C 3h symmetry Frenkel exciton model expressions (see Table S2e states, triphenylamine core is not that active, charge redistribution is partially restricted, and the CDD distribution is slightly different from the expressions of an ideal C 3h symmetry Frenkel exciton model.…”

“…46,72 Since the selection rule is different for two-photon absorption from the one-photon absorption, 13,72 two-photon absorption is one of the most important nonlinear optical properties of organic charge-transfer molecules, which is strongly dependent on the molecular structure, such as electron donor and acceptor features, π-bridge group and length, geometric configuration, etc.…”

Nonlinear optical properties of natural laccaic acid dye studied using Z-scan technique

“…This class of materials is extended to natural dyes which demonstrate a great interest in the field of NLO due to their high delocalized p-electron systems. Such functional materials are of special interest in the area of optical communications, optical storage, optical computing, harmonic generation, optical switching, and optical power limiting [4][5][6][7][8][9][10]. Several environmentally friendly and cost effective natural dyes including the family of chlorophyll [11], carotenoids [12] red Carmine, Chinese tea and betanin, Hibiscus sabdariffa as well as, recently, functionalized DNA [13][14][15][16][17][18] have been investigated.…”