Deactivation mechanism of excited acridine and 9-substituted acridines in water

Abstract

The deactivation processes of excited acridine, deuterated acridine, and 9-substituted acridines (9-methyl, 9-propyl, 9-chloro, and %amino) have been investigated in alkaline and acidic water. The photoreaction does not occur with the irradiation of 365-nm light. In acidic water the fluorescence lifetime T depends only slightly on the temperature and the lowest triplet yield +sT is negligibly low for all of the acridines. In alkaline water T decreases and +ST increases with increasing temperature; the intersystem crossing occurs through both temperaturedependent and temperature-independent processes. For all of the acridines except for 9-aminoacridine, the temperature-dependent process was attributed to the S1(a,a*) + (+Ai?) Sz(n,a*) -T3(a,a*) transition and the temperature-independent process mostly to the Sl(a,a*) -T2(n,a*) transition. The fact that the frequency factor of the temperature-dependent process increases with decreasing the energy gap between S2(n,a*) and S3(a,a*) was interpreted by the vibronic interaction between these states. In the case of 9-aminoacridine, the temperature dependence of r was tentatively attributed to the Sl(a,a*) -(+a) T2(n,a*) transition, because the energy level of T2(n,a*) was considered to be higher than that of Sl(a,a*) in contrast to the other acridines.

Long‐Lived Charge‐Transfer States in Compact Donor–Acceptor Dyads

“…Figure 8) on the acridinium chromophore (E T % 2.0 eV). [43,44] On closer inspection, we note that the transient absorption spectrum attributed to the CT state of 8 is somewhat similar to that expected for the T 1 -T n absorption of the acridinium chromophore. [45] This might make it difficult to discriminate between these species.…”

“…Such interaction is, however, very evident in the fluorescence spectrum. Whereas the isolated acridinium ion is known to display a strong and structured green fluorescence (maximum around 495 nm), [43,47] this is fully quenched in 9 and substituted by a weak, broad, and structureless emission in the far-red region (maximum 675 nm in acetonitrile). This behavior has been observed before and, without doubt, can be attributed to CT fluorescence, that is, emissive back electron transfer from a 1 CT state populated by charge transfer from the naphthyl donor to the acridinium ion.…”

Excited state relaxation of 9-(4-diethylaminostyryl)-acridine

“…Triplet state formation [11][12][13], excited state reduction [14,15], and relaxation between excited ππ * and nπ * states [11,[16][17][18] were reported for different acridine derivatives. The triplet state formation in some of acridines takes place very efficiently, however, it has already been reported [10] that there is no evidence of triplet state population of DSA dyes.…”

“…These states were found to play a crucial role in the excited state relaxation of some acridine derivatives [11,[16][17][18]. In most cases, the nπ * state of acridines is slightly higher than the ππ * state, however, it was also suggested that positions of ππ * and nπ * states in aprotic solvents may be inverted [12,20,21].…”

“…In most cases, the nπ * state of acridines is slightly higher than the ππ * state, however, it was also suggested that positions of ππ * and nπ * states in aprotic solvents may be inverted [12,20,21]. But not of the 9-aminoacridines, where the gap between the ππ * and nπ * states is significantly larger [17]. This is evidently because DSA molecules have enlarged π electron system, which leads to the ππ * state energy reduction, whereas it should not influence the energy of the nπ * state.…”