Ultrafast intramolecular charge transfer in tetrapyrazinoporphyrazines controls the quantum yields of fluorescence and singlet oxygen

• Published in: Physical chemistry chemical physics : PCCP Vol. 12; no. 11; pp. 2555 - 2563
• Main Authors: NOVAKOVA, Veronika, ZIMCIK, Petr, MILETIN, Miroslav, VACHOVA, Lenka, KOPECKY, Kamil, LANG, Kamil, CHABERA, Pavel, POLIVKA, Tomáš
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 01.01.2010
• Subjects: Chemistry; Exact sciences and technology; Fluorescence; General and physical chemistry; Indoles - chemical synthesis; Indoles - chemistry; Oxidation-Reduction; Photochemical Processes; Quantum Theory; Singlet Oxygen - chemistry; Spectrophotometry, Ultraviolet; Nitrogen heterocycle; Fluorescence; Strong coupling; Radiative lifetimes; Intramolecular charge transfer; Pyridine derivatives; Isomer; Macrocycle; Transients; Cyclic voltammetry; Relaxation; Efficiency; Six membered ring; fs range; Polarity; Oxygen; Hydrocarbon; Polar solvent; Zinc II; Toluene; Quantum yield; Steady state; Absorption spectrometry; Pyridine; Benzenic compound; Protonation; Excited state
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/b918546a

A series of octasubstituted zinc(II) tetrapyrazinoporphyrazines (TPyzPz), aza-analogues of phthalocyanines, differing in the number of peripheral N,N-diethylamino (n = 0-8) and tert-butylsulfanyl substituents (m = 8-n) has been synthesized. All possible congeners were characterized including adjacent and opposite isomers. Steady-state (UV-vis, fluorescence) and time-resolved (fluorescence, femtosecond transient absorption) spectroscopies, redox and photochemical (singlet oxygen formation) properties were investigated and compared. The peripheral tertiary amino substituents (donor) induce a new competitive relaxation pathway to fluorescence and intersystem crossing due to the mixing of the first excited state S(1) of the TPyzPz macrocycle with a nearby intramolecular charge transfer (ICT) state. The fluorescence quantum yield and fluorescence lifetime of 6Zn bearing one N,N-diethylamino substituent (n = 1, m = 7) decreased with increasing solvent polarity, while the same observables of 5Zn with no donor centre (n = 0, m = 8) were not affected. Protonation of the N,N-diethylamino substituent in 6Zn led to a strong increase of the fluorescence intensity. The cyclic voltammetry data, the steady-state and time-resolved emission and transient absorption studies revealed strong electronic coupling between the TPyzPz moiety and N,N-diethylamino substituents. ICT is an extremely rapid process occurring with a time constant of 10 ps and 7 ps in 6Zn (n = 1, m = 7) and 11Zn (n = 8, m = 0) in pyridine, respectively. The ICT efficiency decreased in non-polar solvents. The presence of two N,N-diethylamino substituents in 7Zn (n = 2, m = 6) considerably quenched the S(1) states in pyridine (polar, coordinating), toluene (non-polar, non-coordinating) and toluene-1% pyridine (v/v) (non-polar, coordinating). The photophysical properties of compounds with more donor substituents on the periphery (n > 2, m < 6) were similar to those of 7Zn.