Because of this exceptionally high kp, the RTP of 1a in solution was weak but visible even in air (p = 2.6%, Figure , and Supporting Movie 1). We also note that the estimation of kp in the most of previous literatures assumed ISC = 1 without evaluating the time constant of ISC, which may cause errors in the calculation of kp. Experimental evaluation of ISC is essential to the quantitative evaluation of kp.