The afterglow of phosphorescent compounds can be distinguished from background fluorescence and scattered light by a time-resolved observation, which is a beneficial property for bioimaging. Phosphorescence emission accompanies spin-forbidden transitions from an excited singlet state through an excited triplet state to a ground singlet state. Since these intersystem crossings are facilitated usually by the heavy-atom effect, metal-free organic solids are seldom phosphorescent, although these solids have recently been refurbished as low-cost, eco-friendly phosphorescent materials. Here, we show that crystalline isophthalic acid exhibits room-temperature phosphorescence with an afterglow that lasts several seconds through a nuclear spin magnetism-assisted spin exchange of a radical ion pair. The obvious afterglow that facilitates a time-resolved detection and the unusual phosphorescence mechanism that enables emission intensification by nuclear spin managements are promising for exploiting the phosphorescence materials in novel applications such as bioimaging.

Room‐temperature phosphorescence (RTP) of crystalline isophthalic acid (IPA) through hyperfine‐coupling‐driven (HFC‐driven) intersystem crossing in charge‐transfer (CT) complexes has been discovered recently, giving rise to a new design method for phosphorescence materials and photosensitizers. In this study, we found that crystalline phenylboronic acid (PB) derivatives also demonstrated RTP, as recorded for IPA. Magnetic‐field and spin‐isotope effects on the emission strength intensities of PBs were typical of HFC‐driven phosphorescence. p‐Halogenated PB esters exhibited a heavy‐atom effect with a shortened emission lifetime as expected from the study of IPA. Unlike IPA, the esters of PBs also showed RTP, which facilitates a study of the structure/photophysical property relationships by exchanging ester head groups. We then addressed a question: do PB esters with a bulky head group prohibit CT formation and thus phosphorescence? As a result, a bulky PB ester with large intermolecular distances in its crystalline form showed neither CT absorptions nor phosphorescence, confirming the significance of CT formation in the HFC mechanism.

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Cultured cells derived from micromeres isolated from sea urchin embryos at the 16 cell stage are known to show outgrowth of pseudopodial cables followed by spicule rod formation when cultured in the presence of horse serum. Micromere-derived cells cultured with bovine insulin showed pseudopodial cable growth but did not produce spicule rods. Micromere-derived cells reversibly bound to insulin through out the period between 3 and 20 hr of culture. The dissociation constant of insulin with these cells was about 5.1 x 1 O-'OM during the whole culture period examined. Horse serum, as well as blastocoelic fluid obtained from early gastrulae, concentration-dependently reduced the amount of insulin bound to these cells, but the bound insulin was scarcely replaced by any proteins tested, such as bovine serum albumin. The micromerederived cells were bound to have an insulin-binding protein, that may be the receptor for insulin or insulin-like proteins. The insulin-binding protein had a smaller molecular weight than the insulin receptor of mammalian cells. The binding of insulin with this protein in micromere-derived cells probably results in pseudopodial cable growth.

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Reports on the room temperature phosphorescence of metalfree organic crystals have been surging in the past few years. Together with interests in the rare phenomenon, these compounds have attracted attention for such potential applications as bio-imaging probes, oxygen sensors, and organic lightemitting diodes. For common organic compounds, phosphorescence is the emission from a triplet excited state, which is usually produced from a singlet excited state through intersystem crossing, a forbidden spin-flip of an electron. The mechanism of the forbidden process is the key to understanding such rare phenomenon and designing new phosphorescence materials. In this account, we make commentaries on the main intersystem crossing mechanisms proposed to date of the room temperature phosphorescence of heavy-atom-free, crystalline organic compounds, focusing on our own findings.

Pervaporation of an acetic acid/water mixture was studied through synthetic polymeric membranes made from poly(1‐butyl methacrylate), poly(2‐ethylhexyl methacrylate), polystyrene, and copolymers of 4‐vinylpyridine and styrene, whose mole fraction of 4‐vinylpyridine was 0.028 or 0.050. Permselectivities through polystyrene and poly(4‐vinylpyridine‐co‐styrene) (mole fraction of 4‐vinylpyridine, 0.050) are discussed based on the solution‐diffusion theory. © 1994 John Wiley & Sons, Inc.

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