**Yoshiyuki Kageyama**

Faculty of Science, Hokkaido University, Hokkaido 060-0810, Japan; y.kageyama@sci.hokudai.ac.jp; Tel.: +81-11-706-3532

Received: 8 September 2020; Accepted: 10 October 2020; Published: 14 October 2020

**Abstract:** The construction of molecular robot-like objects that imitate living things is an important challenge for current chemists. Such molecular devices are expected to perform their duties robustly to carry out mechanical motion, process information, and make independent decisions. Dissipative self-organization plays an essential role in meeting these purposes. To produce a micro-robot that can perform the above tasks autonomously as a single entity, a function generator is required. Although many elegant review articles featuring chemical devices that mimic biological mechanical functions have been published recently, the dissipative structure, which is the minimum requirement for mimicking these functions, has not been sufficiently discussed. This article aims to show clearly that dissipative self-organization is a phenomenon involving autonomy, robustness, mechanical functions, and energy transformation. Moreover, it reports the results of recent experiments with an autonomous light-driven molecular device that achieves all of these features. In addition, a chemical model of cell-amplification is also discussed to focus on the generation of hierarchical movement by dissipative self-organization. By reviewing this research, it may be perceived that mainstream approaches to synthetic chemistry have not always been appropriate. In summary, the author proposes that the integration of catalytic functions is a key issue for the creation of autonomous microarchitecture.

**Keywords:** dissipative structure; energy conversion; mechanical work; self-oscillation; collective dynamics; autonomous motion; self-replication; autocatalysis; molecular motor; molecular robot

#### **1. Introduction**

It is one of the dreams of chemists to create life or its imitative system using a synthetic chemical method [1,2]. Life is thought to be a collection of nanomachines, and their cooperative behavior is capable of performing work continually in a stationary environment. The process termed 'dissipative self-organization' is one of the key processes involved in this framework [3]. On the other hand, typical inanimate objects in which modules are not self-organized can only perform work passively under transient environmental conditions. Here, work is broadly defined to denote the transfer of energy to the surroundings in a form other than thermal motion; the mechanical work this involves is defined in Section 2. The function of continuously developing in a stationary environment is defined as an autonomous function; autonomy is the realization of continuity by the internal factors of the system.

For example, fluorescent molecules emit light continuously in a photostationary state; catalyst molecules continuously convert reactive substrates into reaction products. The continuous function of these molecules (broadly defined as 'work') is derived from the fact that the molecules consist of self-organized nuclei and electrons. Focusing on such electronic characteristics at the molecular scale, a substantial number of chemical studies have been conducted. Because molecular structures effectively represent the self-organized forms of nuclei and electrons, chemists can predict and consider various functions by examining molecular structural formulas and calculating the density of their electron distributions, while studying phenomena from the perspective of these electronic properties.

This paper describes the autonomous function of molecular assembly generated by molecular self-organization. This concept realizes continuous work at a larger level than the molecular level. It is a concept of nanotechnology that is expected to be applied to material transfer devices and molecular robots and computers and to drive innovation in the field of energy research. Dissipative self-organization remains an attractive keyword for current chemistry. On the other hand, the present author is uncertain whether or not our community genuinely values the concept of dissipative self-organization. One reason for this doubt lies in the fact that the conceptual vocabulary and approaches of nonequilibrium thermodynamics are challenging for chemists who perform their experiments in a flask. Another reason is that clearly realized studies of dissipative self-organization in synthetic chemistry are limited in number. Besides, capturing a temporally developing phenomenon in a printed research paper is not easy. In addition, the terms of self-organization and self-assembly are frequently synonymous; in Japanese, for instance, they are the same word. In this paper, the basic concept of dissipative self-organization is defined in order to underline its importance to current chemical research, and recent developments in synthetic studies are reviewed. It should be noted that the origin of symmetry-breaking is not discussed in this paper.
