Effect of dimer formation on the triplet states of organic dyes

Abstract

Figure 1.computer program written for this purpose, it is clear that the interpretation is incorrect.I n order to obtain an improved interpretation, several deuterated compounds based on the 2,4,5triphenylimidazolyl radical were prepared and their esr spectra recorded. The spectrum of 2,4,5-trideuteriophenylimidazolyl contained five partially resolved lines, corresponding to a nitrogen splitting constant of about 1.63 G. To indicate the relative magnitudes of the different proton splittings in the phenyl rings, a blcLachlan2 calculation was performed using the following parameters: hi+ = 0.5 ~CCN = 1.0 X 1.2. Molecular models showed that the 4-and 5-phenyl rings were twisted out of coplanarity with the imidazolyl ring. The resonance integral between the rings was set to 0.76p corresponding to an angle of twist of about 41". The spin densities calculated by this method are given in Table I, together with the Table I ortho meta para ortho' meta' para' 0.0427 -0,0167 0,045 0,0679 -0,0265 0.072 Spin density Splitting, G 1.01 0.38 1.07 1.61 0.63 1.71calculated splittings assuming a Q of 23.7 G. With the nitrogen splitting constant at 1.44 G, spectra were computed for varying Q values. It was then found that the best fit with number, intensity, and separation of lines was with a slightly higher proportion of the spin density on the para' proton; the splittings (in gauss) are: ortho, 1.45; meta, 0.55; para, 1.52; ortho', 2.33; meta', 0.92; and para', 2.98. The line shape used was 100% gaussian and the line width at half-power for any line was set at 0.15 G. The observed and theoretical spectra are shown in Figure 2. As a further test of the correctness of this interpretation, esr spectra were calculated for the 2-deuteriophenyl-4,5-diphenylimidazolyl, the 2-phenyl-4,5-dideuteriophenylimidazolyl, , Jeaurrs, Figure 2.B is the simulated spectrum.A is the experimental spectrum; and the fully deuterated material. The deuterium splittings were obtained by reducing the proton splittings by a factor of 6.514 and setting the nuclear spin to 1. The experimental and theoretical plots were in good agreement. The splittings suggest that the paramters used in the preliminary McLachlan calculation are capable of improvement; it is hoped to find parameters which will give a good fit with the spectrum of this compound and with the spectra of substituted compounds.(2) A. D. McLachlan, Mol. Phys., 3, 233 (1960).

Generation of Phosphorescent Triplet States via Photoinduced Electron Transfer: Energy and Electron Transfer Dynamics in Pt Porphyrin–Rhodamine B Dyads

“…Apparently, equilibrium is established between these two states, forming a pool of triplet excitons. The existence of the equilibrium is supported by the fact that the energy of T1 RhB + (1.80-1.84 eV) 69-71 is almost equal to that of T1 PtP (1.85 eV), and the energetics of T1 pRhB + → T1 PtP process is not completely unfavorable. Furthermore, phosphorescence measurements at 77K (Fig.…”

Effect of dimer formation on the electronic absorption and emission spectra of ionic dyes. Rhodamines and other common dyes

“…Since many of the commonly used dyes tend to aggregate and form dimers in solutions, a number of the studies carried out during the past 10 years have been concerned with understanding the spectral effects produced by dimerization. [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] In the experimental studies which have been carried out so far, the emphasis has been on measurement of spectral shifts of bands, hypochromism, and changes in vibronic structure produced by dimerization. Insofar as we are aware, there has been no measurement of the polarization of the electronic transitions in the dimers, despite the fact that most theoretical treatments of dimer spectra give strong predictions regarding the polarization of transitions in the dimer.…”

Excimer fluorescence and dimer phosphorescence from a naphthalene sandwich pair

“…the fluorescence) naphthalene molecule at 77 °K. If the formation of an excimer were hindered because of an activation energy we can set a lower limit of 4 kcal mole-1 for this £a, based on a rate of less than 1 sec-1 and an A factor > 1012. It does not seem reasonable that there should be such a barrier in view of the absence of a barrier to formation of a singlet excimer, which rules out any steric factors, either intramolecular or involving the matrix.…”