The S1 electronic state of 7,7,8,8‐Tetracyanoquinodimethane (TCNQ) has been investigated by laser induced fluorescence (LIF), dispersed fluorescence (DF) spectroscopy, and lifetime measurements under jet‐cooled conditions in the gas‐phase. The LIF spectrum showed a weak origin band at 412.13 nm (24262 cm−1) with prominent progression and combination bands involving vibrations of 327, 1098, and 2430 cm−1. In addition, very strong bands appeared at ∼363.6 nm (3300 cm−1 above the origin). Both the LIF and DF spectra indicate considerable geometric change in the S1 state. The fluorescence lifetime of S1 at zero‐point level was obtained to be 220 ns. This lifetime is 40 times longer than the radiative lifetime estimated from the S1−S0 oscillator strength. Furthermore, the lifetimes of the vibronic bands exhibited drastic energy dependence, indicating a strong mixing with the triplet (T1) or intramolecular charge‐transfer (CT) state. This study is thought to disclose intrinsic nature of TCNQ, which has been well known as a component of organic semiconductors and a versatile p‐type dopant.

No abstract

We performed UV spectroscopy for p-coumaric acid (pCA), ferulic acid (FA), and caffeic acid (CafA) under jet-cooled gas-phase conditions by using a laser-ablation source. These molecules showed the S1(1ππ*)–S0 absorption in the 31 500–33 500 cm–1 region. Both pCA and FA exhibited sharp vibronic bands, while CafA showed only a broad feature. The decay time profile of the 1ππ* state was measured by picosecond pump–probe spectroscopy, and the transient state produced through the nonradiative decay (NRD) from 1ππ* and its time profile were measured by nanosecond UV–deep UV pump–probe spectroscopy. The transient state was observed for pCA and FA and assigned to the T1 state, and we concluded that the NRD process of 1ππ* is S1(1ππ*) → 1nπ* → T1(3ππ*), similar to those of methyl cinnamate and para-substituted cinnamates such as p-hydroxy and p-methoxy methyl cinnamate. On the other hand, the transient T1 state was not detected in CafA, and its NRD route is suggested to be S1(1ππ*) → 1πσ* → H atom elimination, similar to those of phenol and catechol. The effect of a hydrogen bond on the electronic state and NRD process was investigated, and it was found that the H-bonding lowers the 1ππ* energy and suppresses the NRD process for all the species.

The front cover artwork is provided by the groups of Prof. Takayuki Ebata, Prof. Yoshiya Inokuchi at Hiroshima University, and Prof. Toshifumi Iimori at Muroran Institute of Technology. The image shows the first laser spectroscopic study of jet‐cooled TCNQ in the gas‐phase, which is compared with the absorption and emission in solution. Read the full text of the Communication at 10.1002/cphc.201900214.

The Front Cover illustrates the first laser spectroscopic study of jet‐cooled TCNQ in the gas‐phase, which is compared with the absorption and emission in solution. More information can be found in the Communication by N. Chaki et al. on page 996 in Issue 8, 2019 (DOI: 10.1002/cphc.201900214).