Fluorescence and phosphorescence emission and nonradiative relaxation of acridine in a crystalline matrix of 2,3-dimethylnaphthalene

Emission of Acridine and its Aggregates Isolated in the Neon Matrix

“…Such an assignment locates the first excited singlet state (of mixed electronic character) of ACD molecule in the neon matrix at 27050 cm -1 , i.e., at the energy of cα. 300-400 cm -1 higher than the energy of its S1 (presumably of n., π* character) state in n-hexane [4] and of 1000 cm -1 higher than in such matrices as low-temperature PMMA glass [5] or crystalline matrix of DMN [17]. It is known that the third excited triplet state Τ3 of π, π* character is located in the range of 26000-26500 cm -1 and that its position within this range is almost solvent-independent [5,13,17,30].…”

“…300-400 cm -1 higher than the energy of its S1 (presumably of n., π* character) state in n-hexane [4] and of 1000 cm -1 higher than in such matrices as low-temperature PMMA glass [5] or crystalline matrix of DMN [17]. It is known that the third excited triplet state Τ3 of π, π* character is located in the range of 26000-26500 cm -1 and that its position within this range is almost solvent-independent [5,13,17,30]. With the mixed character of S1 state this would facilitate Sl--->Τ3 intersystem crossing, which followed by the internal conversion within the triplet manifold would result in the observation of measurable phosphorescence.…”

“…3a). The 0-0 band of the phosphorescence is positioned at 16016 cm-1 and thus it has a higher energy than the 0-0 band of phosphorescence of ACD in chemically mixed crystal of ACD (host) with anthracene -15691 cm -1 [25] and in crystalline host matrices of fluorene -15749 cm -1 [23] and of dimethylnaphthalene -15813 cm -1 [17] or in PMMA matrix (at 77 K) -15800-15900 cm -1 [5]. The observed phosphorescence spectrum contains such vibrational frequencies as 246, 401, 622, 1170 and 1271 cm -1 , all of them have been previously observed in the phosphorescence spectrum of ACD in the -fluorene crystalline host matrix at 2.2 K [23], and also frequencies of 790, 876 and 1410 cm -1 known from either IR or Raman spectra of ACD [26].…”

“…In such crystalline host matrices as biphenyl [15] and fluorene [16] the lowest excited singlet state may be of strong 1 (n, π*) character. On the other hand in crystalline host matrix of 2,3-dimethylnaphthalene (DMN) the lowest excited singlet state of ACD must be of 1 (π, π*) character as inferred from a relatively strong and weakly temperature-dependent fluorescence with a rather long decay time of 8 ns at 4.2 Κ [17]. In addition, in this case also a very strong phosphorescence of ACD is observed with very moderate intensity changes (of ca.…”

Spectroscopy and Photophysics of Monoazaphenanthrenes III. Luminescence of Phenanthridine and 7,8-benzoquinoline in Crystalline State

“…At this point we should mention that temperature changes of the fluorescence spectrum of polycrystalline samples of PHN recall to some extent of temperature changes of fluorescence of chemically mixed crystals, especially those formed with acridine (i.e. monoazaanthracene) serving as a guest in other crystalline matrices [17][18][19]. However, polycrystalline samples of PHN should probably be considered as more amorphous than single crystals, and other factors (characterizing imperfections in the bulk of tiny crystallites) must be taken into account in the description of observed temperature changes of the fluorescence.…”