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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Optical and time-resolved electron paramagnetic resonance studies of the excited states of a UV-B absorber (4-methylbenzylidene)camphor
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Optical and time-resolved electron paramagnetic resonance studies of the excited states of a UV-B absorber (4-methylbenzylidene)camphor

机译：UV-B吸收剂（4-甲基亚苄基）樟脑丸激发态的光学和时间分辨电子顺磁共振研究

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摘要

The excited states of UV-B absorber (4-methylbenzylidene)camphor (MBC) have been studied through measurements of UV absorption, phosphorescence, triplet-triplet (T-T) absorption, and steady-state and time-resolved electron paramagnetic resonance spectra in ethanol. The energy level and lifetime of the lowest excited triplet (T_1) state of MBC were determined. The energy level of the T1state of MBC is much lower than that of photolabile 4-tert-butyl-4′-methoxydibenzoylmethane. The weak phosphorescence and strong time-resolved EPR signals, and T-T absorption band of MBC were observed. These facts suggest that the significant proportion of the lowest excited singlet (S_1) molecules undergoes intersystem crossing to the T 1state and the deactivation process from the T1state is predominantly radiationless. The quantum yields of singlet oxygen production by MBC determined by time-resolved near-IR luminescence measurements are 0.05 ± 0.01 and 0.06 ± 0.01 in ethanol and in acetonitrile, respectively. The photostability of MBC arises from the ~3ππ* character in the T1state. The zero-field splitting parameters in the T_1state are D = 0.0901 cm~(-1) and E = -0.0498 cm~(-1). The sublevel preferentially populated by intersystem crossing is T_y (y close to in-plane short axis and to the C=O direction).
机译：通过测量乙醇中的UV吸收，磷光，三重态三重态（TT）吸收以及稳态和时间分辨的电子顺磁共振光谱，研究了UV-B吸收剂（4-甲基亚苄基）樟脑（MBC）的激发态。 。确定了MBC的最低激发三重态（T_1）状态的能级和寿命。 MBC的T1state的能级远低于光不稳定的4-叔丁基-4'-甲氧基二苯甲酰甲烷。观察到微弱的磷光和强的时间分辨的EPR信号，以及MBC的T-T吸收带。这些事实表明，最低比例的激发单线态（S_1）分子有较大的系统间交叉，与T 1状态发生交叉，并且从T1状态起的失活过程主要是无辐射的。通过时间分辨的近红外发光测量确定的MBC产生单线态氧的量子产率在乙醇和乙腈中分别为0.05±0.01和0.06±0.01。 MBC的光稳定性来自于T1状态下的〜3ππ*字符。在T_1状态下的零场分裂参数为D = 0.0901 cm〜（-1）和E = -0.0498 cm〜（-1）。优先通过系统间交叉填充的子级别为T_y（y靠近平面内短轴并接近C = O方向）。

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