Dual Fluorescence in a Schiff Base Derived from an Acridinedione Dye. Excited State Intramolecular Proton Transfer

Abstract

Newly synthesized nonconjugated, but covalently linked, bichromophoric systems (ADDSA) contain a salicylideneaniline (SA) moiety linked to an acridinedione (ADD) fluorophore via a covalent bond. The absorption and fluorescence characteristics of the ADDSA systems in various solvents reveal that the dual fluorescence originates from two different chromophores in the same molecule. The solvent polarity independent, long wavelength anomalous emission originates from the keto form of SA moiety via excited state intramolecular proton transfer (ESIPT). The ESIPT pathway was further confirmed by the benzylideneaniline (BA) and ADD moieties coupled non-proton transfer model system (ADDBA). Absence of the longer wavelength anomalous emission in the steady state as well as the shorter lifetime component in the time-resolved study for ADDBA system supports ESIPT mechanism for long wavelength anomalous emission in ADDSA system. ESIPT, discovered by Weller in 1955, has been the subject of continuous interest of researchers for more than five decades. 1 Photoinduced proton transfer, which is a representative of a limited number of adiabatic photochemical processes giving rise to fluorescence with an abnormally large Stokes shift, 2 plays an important role in biophysics, 3 and has practical application in technology, for example, in organic scintillators. 4 Among the molecular systems characterised by excited state proton transfer, both efficient organic photochromes 5 and polymer ultraviolet stabilisers 6 are of much interest. Prospects for the use of ESIPT systems in luminescent solar energy concentrators have also been discussed in literature. 7 For the ESIPT reaction to occur, it is necessary that proton-donor and proton-acceptor moieties be in close proximity and conjugated to one another in an organic molecule. ESIPT is considered as the driving force for the concerted enhancement of their acidity or basicity upon the transition to an excited state. 8 If a molecule carries its own base, excited-state proton transfer can occur intramolecularly and becomes more or less independent of the surrounding solvent. ESIPT reaction is extremely fast (subpicosecond kinetics) and also occurs in rigid glasses and at very low temperatures. 9 Very often, only the ESIPT product (P Ã ) fluoresces, and this is the source of extremely large Stokes shift, which are fairly independent of medium and temperature. Thus, ESIPT dyes are ideal candidates for use as fluorescence labels in order to avoid interference from other fluorescent material present in the sample to be analyzed.Most of the publications on ESIPT deal with derivatives of salicylic acid, its esters and amides, 10 salicylaldehyde, acetophenone and related compounds, 11 o-hydroxybenzoxazoles, 12 benzothiazoles, 13 triazoles, 14 flavonols, 15 anthraquinones, 16 bipyridyls, 17 and malonic aldehyde. 18 Recently, Chou et al. have studied the solvent polarity tuned excited state, charge-transfer-coupled proton transfer reaction in p-N,N-ditolylaminosalicylaldehyde-and 3-hydroxyflavone-ba...

Modulation of excited state intramolecular proton transfer and intramolecular charge transfer pathways of symmetrical azines through micellar medium

“…Interestingly, both the molecules show emission maximum around 530 nm in the solid state and also independent of the excitation wavelengths which in turn confirms the newly formed 530 nm emission in ionic micelles for DEASAD is due to the keto state formation in the excited state through ESIPT pathway. Similar emission maximum (530 nm) was observed for keto form of salicylideneaniline (SA) chromophore through ESIPT reaction in a nonconjugated, but covalently linked, bichromophoric systems contain SA moiety linked to an acridinedione fluorophore via a covalent bond 37 . As compared to solid‐state emission, 20 nm red shifted emission observed for SAD (550 nm) in micelles which may be due to the presence of different conformations in solid and liquid state.…”

“…Similar emission maximum (530 nm) was observed for keto form of salicylideneaniline (SA) chromophore through ESIPT reaction in a nonconjugated, but covalently linked, bichromophoric systems contain SA moiety linked to an acridinedione fluorophore via a covalent bond. 37 As compared to solid-state emission, 20 nm red shifted emission observed for SAD (550 nm) in micelles which may be due to the presence of different conformations in solid and liquid state.…”

Effect of benzene ring on the excited‐state intramolecular proton transfer mechanisms of hydroxyquinoline derivatives

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] The excited-state intramolecular proton transfer (ESIPT), as a fundamental process, has been investigated both experimentally and theoretically by many groups since the first experimental observation of the phenomenon by Weller and coworkers in 1965. [21][22][23][24][25][26][27] In recent years, the ESIPT phenomenon continues to be an active researching area due to its significant applications in molecular logic gates, [28][29][30] molecular probes, [31][32][33][34] organic light-emitting devices, [35] laser dyes, [36][37][38][39] and luminescent materials. [35,40,41] The ESIPT processes can occur from the proton donor groups (e.g., ─OH and ─NH 2 ) to the proton accept groups (e.g., ─C═O and pyridinyl nitrogen atom).…”

Insight into the excited-state intramolecular double-proton transfer of the 2,5-bis(benzoxazol-2-yl)thiophene-3,4-diol: one-step or stepwise mechanism?

“…The excitedstate intramolecular proton transfer (ESIPT) attracts much attention particularly due to its dual emission with large Stokes' shift, which leads to its significant applications in molecular probes [5,[13][14][15][16], laser dyes [17][18][19], luminescent materials [20][21][22], chemosensors [23][24][25][26][27][28][29][30][31] and molecular logic gates [32], etc. Hence, the mechanism investigation of ESIPT is of vital importance to design, synthesize and regulate desired luminescent molecules [33][34][35][36][37].…”