Absorption and Emission Spectra of

The total energy of a diatomic molecule may be separated into translational energy and internal energy. We are concerned here with the internal energy which can be expressed to a good approximation by where E, is the electronic 

Potential-energy diagram for molecular iodine. The energy zero has been arbitrarily set at the minimum of the ground-state potential. 

The rotational-term difference Flv, J) F v , J ) will be ignored, since the rotational structure is not resolved in this experiment. The cubic term in G v) is also small and can be neglected in obtaining the transition frequency 

If the quantum numbers v and v are known, the measured frequencies in an absorption or emission spectrum can then be used with a multiple linear least-squares technique (see Chapter XXI) to determine the parameters v j, v g,Vgx g,vX, and r x g. 

An alternative analysis procedure that is often used concentrates on the determination of T g r gAg parameters within each electronic state. Differences between levels in the upper state are obtained from 

---

One interesting new field in the area of optical spectroscopy is near-field scaiming optical microscopy, a teclmique that allows for the imaging of surfaces down to sub-micron resolution and for the detection and characterization of single molecules [, M]- Wlien applied to the study of surfaces, this approach is capable of identifying individual adsorbates, as in the case of oxazine molecules dispersed on a polymer film, illustrated in figure Bl.22,11 [82], Absorption and emission spectra of individual molecules can be obtamed with this teclmique as well, and time-dependent measurements can be used to follow the dynamics of surface processes. 

The characteristic lines observed in the absorption (and emission) spectra of nearly isolated atoms and ions due to transitions between quantum levels are extremely sharp. As a result, their wavelengths (photon energies) can be determined with great accuracy. The lines are characteristic of a particular atom or ion and can be used for identification purposes. Molecular spectra, while usually less sharp than atomic spectra, are also relatively sharp. Positions of spectral lines can be determined with sufficient accuracy to verify the electronic structure of the molecules. 

Absorption and emission spectra of six 2-substituted imidazo[4,5-/]quinolines (R = H, Me, CH2Ph, Ph, 2-Py, R = H CH2Ph, R = Ph) were studied in various solvents. These studies revealed a solvent-independent, substituent-dependent character of the title compounds. They also exhibited bathochromic shifts in acidic and basic solutions. The phenyl group in the 2-position is in complete conjugation with the imidazoquinoline moiety. The fluorescence spectra of the compounds exhibited a solvent dependency, and, on changing to polar solvents, bathochromic shifts occur. Anomalous bathochromic shifts in water, acidic solution, and a new emission band in methanol are attributed to the protonated imidazoquinoline in the excited state. Basic solutions quench fluorescence (87IJC187). 

A xylylene-fc/.v-phosphonium salt 11 gave films of PPV 1 upon clectropolymer-ization. The absorption and emission spectra of the resultant material were blue-shifted with respect to PPV produced by other routes, suggesting that the electro-polymerized material has a shorter effective conjugation length, possibly because of incomplete elimination of phosphonium groups [22]. 

A comparison of the absorption and emission spectra of Ooct-OPV5 with those of the fully conjugated, similarly substituted polymer Ooct-PPV shows that the absorption and luminescence maxima of the five-ring model compound are only slightly blue-shifted relative to those of the polymer (see Fig. 16-11). Hence, the... 

Figure 4-9. INDO/SCI-simulalcd absorption and emission spectra of two slilbene molecules with a huge interchain distance (solid lines) and those of a cofacial dimer formed by two slilbene chains separated by 4 A (dolled lines).

Absorption and emission spectra of atoms and ions yield information about energy differences between orbitals, but they do not give an orbital s absolute energy. The most direct measurements of orbital energies come from a technique called photoelectron spectroscopy. 

A porphyrin compound with a 2,9-dimethyl- 1,10-phenanthroline functionality fused at the beta-pyrrole positions is a phthalocyanine analog, and formed a complex with zinc in the cavity and a further zinc binding to the phenanthroline group. The absorption and emission spectra of the compound with and without the external zinc demonstrated the strong effects of the second metal binding on the porphyrin 7r-system.840... 

Fig. 1 Absorption and emission spectra of Cy3, CyS, Cy7, oxo-squaraine 13b (part 3 of this chapter) and dicyanomethylene squaraine 41j (part 4 of this chapter) in water (pH 7.4)...

Fig. 15 (a) Structure isomers betweenp-HBDI and o-HBDI. (b) The absorption and emission spectra of o-HBDI in cyclohexane (black solid line) and solid film (red solid line, emission only) and o-MBDI blue solid line) in cyclohexane (reprint from ref. [117], Copyright 2007 American Chemical Society)... 

Figure 12.8.8 A schematic representation of the normalized absorption and emission spectra of 7-amino-4-methylcoumarin.

The absorption and emission spectra of a fluorophore are bands spread over a range of wavelengths with at least one peak of maximal absorbance and emission that corresponds to the So-Si and Si—S0 transitions, respectively. There are several vibrational levels within an electronic state and transitions from one electronic to several vibrational states are potentially possible. This determines that the spectra are not sharp but consist of broad bands. The emission spectrum is independent of the excitation wavelength. The energy used to excite the fluorophore to higher electronic and vibrational levels is very rapidly dissipated, sending the fluorophore to the lowest vibrational level of the first electronic excited state (Si) from where the main fluorescent transition occurs [3] (see Fig. 6.1). 

In contrast to Ag, these emission profiles are insensitive to variations of the excitation wavelength within the threefold structure of the 2P 2S absorption band. Simultaneous with the photolysis of any of the three 2P - 2S components, one observes gradual bleaching of all lines with concurrent formation of Ci where n =2-5 (34,56). A further intriguing observation concerns the appearance of a weak structured emission near 420 nm for excitations centered on the secondary atomic site band of Cu in all three rare gas films (Figure 4), which has been found from independent studies of the absorption and emission spectra of matrix entrapped CU2 to arise from the A-state of CU2 (34). 

Figure 4. Absorption and emission spectra of Ru(bpy)s2+ and the excited state transient absorption spectrum of Ru(bpy)s2 Key A, absorption spectrum of Ru(bpy)s2V B, absorption spectrum of Ru(bpy)32+ and C, emission spectrum. Conditions room temperature, and aqueous solution. (Reproduced from Ref. 19c. Copyright 1981, American Chemical Society.)...

FIGURE 2.9 Typical absorption and emission spectra of polyfluorene in thin films (shown for poly(9,9-dioctylfluorene) 196). (From Gong, X., Iyer, P.K., Moses, D., Bazan, G.C., Heeger, A.J., and Xiao, S.S., Adv. Fund. Mater., 13, 325, 2003. With permission.)... 

A very efficient green-emitting fluorene copolymer 304 was synthesized by Shim and coworkers [390] via Suzuki coupling of dibromothieno[3,2-b]thiophene with dialkylfluorene-diboronic acid [390]. The authors compared the EL properties of this copolymer with PFO homopolymer 196 and PFO-bithiophene copolymer 295. Both the absorption and emission spectra of 304 are red-shifted compared with PFO 196 but slightly blue-shifted compared to bithiophene-based copolymer 295. PLEDs fabricated in the configuration ITO/ PEDOT/304/LiF/Al showed a pure green emission (CIE . v 0.29, r 0.63) close to the... 

Absorption and emission spectra of Ti3+ ions in an alumina crystal... 

The reactive excited state in a photochemical reaction is usually either the Si state or the Ti state of the reactant molecule. These states can be characterised by reference to the absorption and emission spectra of the reactant. 

Fig. 11 (a) Chemical structure left, 9 90°) and cation response right) of virtually decoupled probe 30 for Hg2+ and Ag+. Absorption and emission spectra of 30 in the absence (black, dotted line = fit of the CT emission LE = fluorophore-localized emission band) and presence (at full complexation) of Hg2+ red) and Ag+ blue) in MeCN fluorometric titrations of 1 with Hg2+ and Ag+ shown in the inset FEF (LE) determined from the integrated fluorescence intensity of the LE band, (b) Chemical structures of other virtually decoupled probes for Na+ (31), Pb2+ (32), and Ni2+ (33). For color code, see Fig. 3. (Adapted in part from [115], Copyright 2000 American Chemical Society)...

Compared to the absorption and emission spectra of the free dye, the spectra of the rotaxane 5 C a-CD PF6 are sharper and red-shifted. The absorption maximum... 

For instance, the absorption and emission spectra of anthracene show a wave-number spacing of about 1400 cm-1, i.e. an energy spacing of 2.8 x 10 20 J, between the 0 and 1 vibrational levels. In this case, the ratio Ni/N0 at room temperature (298 K) is about 0.001. 

The width of a band in the absorption or emission spectrum of a fluorophore located in a particular microenvironment is a result of two effects homogeneous and inhomogeneous broadening. Homogeneous broadening is due to the existence of a continuous set of vibrational sublevels in each electronic state. Absorption and emission spectra of moderately large and rigid fluorophores in solution could therefore be almost structureless at room temperature. However, in some cases, many of the vibrational modes are not active, neither in absorption nor in emission, so that a dear vibrational structure is observed (e.g. naphthalene, pyrene). 

Figure 1.14. Electronic absorption and emission spectra of Py+ and of Ox+ in aqueous solution (solid) and in zeolite L (dashed). Upper. Py+ absorption and fluorescence (/.L.x — 460 nm) spectra in aqueous solution and excitation (X,em = 560 nm) and fluorescence (/.L.x = 460 nm) spectra in zeolite L suspension. Lower. Ox+ absorption and fluorescence (/.LX = 560 nm) spectra in aqueous solution and excitation (/ em = 640 nm) and fluorescence (X,ex — 560 nm) spectra in zeolite L suspension.

Figure 3.17. Absorption and emission spectra of two blue emitting molecular glasses, Spiro-sexiphenyl (Spiro-6c[>) and 4-Spiro2 in the solid state.

---